Magnetic Susceptibility in 2D Superconductor NaxHfNCl System

Abstract

Superconducting critical temperature, T_c and the shielding volume fraction, SVF, of layered nitride superconductor Na_xHfNCl have been studied as a function of x, i.e. Na concentration. Although T_c decreases gradually with increasing x from 20.0 K at x=0.11 to 16.5 K at x=0.85, SVF has a sharp peak around x=1/6, where strong coupling between local ordering of Na atoms and Fermi surface instability can be expected. Structural disorder in the samples above x=0.5, observed by powder neutron diffraction, does not affect the superconductivity appreciably. Electronic specific heat coefficient, γ, is estimated to be about 7.7 mJ/mol/K² by its difference of magnetic susceptibility between HfNCl and Na_0.5HfNCl. The γ value is relatively small compared with the high T_c value, revealing double honeycomb lattice system as new potential higher T_c superconductor series by intercalation.     

Diffusional kurtosis imaging of cingulate fibers in Parkinson disease: Comparison with conventional diffusion tensor imaging

Objective

The pathological changes in Parkinson disease begin in the brainstem; reach the limbic system and ultimately spread to the cerebral cortex. In Parkinson disease (PD) patients, we evaluated the alteration of cingulate fibers, which comprise part of the limbic system, by using diffusional kurtosis imaging (DKI).

Methods

Seventeen patients with PD and 15 age-matched healthy controls underwent DKI with a 3-T MR imager. Diffusion tensor tractography images of the anterior and posterior cingulum were generated. The mean kurtosis (MK) and conventional diffusion tensor parameters measured along the images in the anterior and posterior cingulum were compared between the groups. Receiver operating characteristic (ROC) analysis was also performed to compare the diagnostic abilities of the MK and conventional diffusion tensor parameters.

Results

The MK and fractional anisotropy (FA) in the anterior cingulum were significantly lower in PD patients than in healthy controls. The area under the ROC curve was 0.912 for MK and 0.747 for FA in the anterior cingulum. MK in the anterior cingulum had the best diagnostic performance (mean cutoff, 0.967; sensitivity, 0.87; specificity, 0.94).

Conclusions

DKI can detect alterations of the anterior cingulum in PD patients more sensitively than can conventional diffusion tensor imaging. Use of DKI can be expected to improve the ability to diagnose PD.     

Variational Proof of the Existence of the Super-Eight Orbit in the Four-Body Problem

Using the variational method, Chenciner and Montgomery (Ann Math 152:881–901, 2000) proved the existence of an eight-shaped periodic solution of the planar three-body problem with equal masses. Just after the discovery, Gerver numerically found a similar periodic solution called “super-eight” in the planar four-body problem with equal mass. In this paper we prove the existence of the super-eight orbit by using the variational method. The difficulty of the proof is to eliminate the possibility of collisions. In order to solve it, we apply the scaling technique established by Tanaka (Ann Inst H Poincaré Anal Non Linéaire 10:215–238, 1993), (Proc Am Math Soc 122:275–284, 1994) and investigate the asymptotic behavior of a binary collision.     

Random-growth urban model with geographical fitness

This paper formulates a random-growth urban model with a notion of geographical fitness. Using techniques of complex-network theory, we study our system as a type of preferential-attachment model with fitness, and we analyze its macro behavior to clarify the properties of the city-size distributions it predicts. First, restricting the geographical fitness to take positive values and using a continuum approach, we show that the city-size distributions predicted by our model asymptotically approach Pareto distributions with coefficients greater than unity. Then, allowing the geographical fitness to take negative values, we perform local coefficient analysis to show that the predicted city-size distributions can deviate from Pareto distributions, as is often observed in actual city-size distributions. As a result, the model we propose can generate a generic class of city-size distributions, including but not limited to Pareto distributions. For applications to city-population projections, our simple model requires randomness only when new cities are created, not during their subsequent growth. This property leads to smooth trajectories of city population growth, in contrast to other models using Gibrat’s law. In addition, a discrete form of our dynamical equations can be used to estimate past city populations based on present-day data; this fact allows quantitative assessment of the performance of our model. Further study is needed to determine appropriate formulas for the geographical fitness.     

Dynamics of polyrotaxane investigated by neutron spin echo

The dynamics of a molecular necklace known as polyrotaxane (PR), in which α-cyclodextrins (CDs) are threaded into a poly (ethylene glycol) (PEG) chain, was investigated by means of neutron spin echo (NSE) measurements. We observed that threading CDs into PEG slowed down the local dynamics and changed its Q-dependence. A solution of PEG in DMSO-d₆ showed a dynamical crossover from collective diffusion dynamics to the Zimm mode, just as in conventional polymer solutions; however, the motion of PR in DMSO-d₆ was diffusive for the whole Q range. This may be because the persistence length l_p of PR was much larger than that of PEG and was similar to the mesh size of PR. The diffusive mode in a high Q regime, corresponding to a length scale of less than the l_p value of PR, contained the mode of the sliding of CDs along a rod-like PEG segment in one dimension.     

Preparation of ionic liquids bearing o-carborane anion via N,N′-dialkylimidazol-2-ylidene carbene

In the present study, a novel ionic liquid including o-carborane anion was prepared. After the carbene formation of 1-ethyl-3-methylimidazolium halide ([EMIm]⁺[X]⁻) by reaction with n-BuLi, the subsequent reaction with o-carborane afforded the desired ionic liquid in moderate yields. The structure of the ionic liquid was supported by ¹H NMR and ¹¹B NMR spectra.     

Highly Elastic and Deformable Hydrogel Formed from Tetra‐arm Polymers

After decades of efforts by many researchers, we have succeeded in realizing a near‐ideal polymer network. This network, the Tetra network, is made by cross‐end‐coupling of tetra‐arm polymer modules. The mechanical energy dissipation was extremely low (tan δ ≈ 10⁻⁴). The macroscopic stress–strain relationship of the Tetra network was in good agreement with that of microscopic elastic blobs. The maximum breaking strength was extremely high (≥27 MPa). These results indicate that the Tetra network is closer to an ideal polymer network than any other conventional model networks. Because the Tetra network can be treated as uniformly packed elastic blobs, it should help apply the knowledge of single polymer chains seamlessly to the design of polymer materials and help further develop the theory of rubber elasticity.

     

Physical properties of 8OS5 thioester studied by complementary methods

ABSTRACT

Properties of 4-n-pentylphenyl-4’-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed.     

Theoretical Study on Redox Potential Control of Iron-Sulfur Cluster by Hydrogen Bonds: A Possibility of Redox Potential Programming

The effect of hydrogen bonds around the active site of Anabaena [2Fe-2S] ferredoxin (Fd) on a vertical ionization potential of the reduced state (IP(red)) is examined based on the density functional theory (DFT) calculations. The results indicate that a single hydrogen bond increases the relative stability of the reduced state, and shifts IP(red) to a reductive side by 0.31–0.33 eV, regardless of the attached sulfur atoms. In addition, the IP(red) value can be changed by the number of hydrogen bonds around the active site. The results also suggest that the redox potential of [2Fe-2S] Fd is controlled by the number of hydrogen bonds because IP(red) is considered to be a major factor in the redox potential. Furthermore, there is a possibility that the redox potentials of artificial iron-sulfur clusters can be finely controlled by the number of the hydrogen bonds attached to the sulfur atoms of the cluster.     

Synthesis of a novel star-shaped dendrimer by radial-growth polymerization of sarcosine N-carboxyanhydride initiated with poly(trimethyleneimine) dendrimer

A novel AB_n-type dendrimer/linear polymer block copolymer, i.e., poly(trimethyleneimine) dendrimer-block-(polysarcosine)₆₄ ( 1 ), was synthesized by ring-opening polymerization of sarcosine N-carboxyanhydride initiated with the 64-NH₂-terminal poly(trimethyleneimine) dendrimer as a macroinitiator. 1 has narrow molecular weight distributions (M_w/M_n = 1.0₁–1.0₃, by size exclusion chromatography) and controlled polysarcosine chain lengths (by varying the monomer/dendrimer feed molar ratios). Small-angle neutron scattering (SANS) data obtained in D₂O solution of 1 (DP's of polysarcosine = 2.0 and 24) fitted well with a Guinier plot of a spherical particle, and gave diameters of 44 and 100 Å, respectively.