Nature © Macmillan Publishers Ltd 19988 the fact that we have a quantized Hall resistance deep inside the insulator. Indeed, j 2 xx j xy 2 e 2 2h 2 e 2 2 h 12e 2 =hr xy r 2 xx r 2 xy simply from matrix inversion. As noted by Shahar et al. 10 , the semicircle relation follows directly as long as r xy h=e 2 . In addition, it is completely independent of the value of r xx . We emphasize that this relation holds for our entire range of T. Ando 21 ®rst calculated numerically the dependence of j xx on j xy and found a similar relation to the semicircle function. In the selfconsistent Born approximation and scaling theories, a behaviour of this kind is also expected 22 . A recent numerical study by R. N. Bhatt and S. Subramanian (personal communication), with symmetric and non-symmetric random potentials in a lowest-Landau-level model, con®rmed this result. For higher Landau levels, Wei et al. 23 and others 10 showed similar dependences. This is, however, the ®rst clear demonstration of this relation for n # 1 and j xx and j xy both smaller than e 2 /2h.The experiments presented covered a certain range of parameters, in particular in temperature and in disorder. Different behaviours occurring at even lower temperatures or higher mobilities are therefore possible and would be interesting to investigate in future. The existence of these insulators, however, can serve as guidelines for a complete understanding of two-dimensional systems in strong magnetic ®elds. M
Intergrain tunneling magnetoresistance ͑TMR͒ subsisting up to room temperature has been observed for polycrystalline ceramics of Sr 2 FeReO 6 , which has ordered double perovskite structure with Curie temperature above 400 K. The first-principles band calculation predicts that Sr 2 FeReO 6 shows the half metallic ground state with the ferrimagnetic coupling of Fe and Re spins. The experimental results of electronic and magnetic properties are in accord with this picture. In fact, the magnitude of intergrain TMR with the magnetic field of 7 T at 4.2 and 300 K is as large as 21 and 7%, respectively, reflecting high spin polarization of carriers.
We report here structural study on solvation of Mg 2+ ion in triglyme (G3)-based solutions applying as a novel electrolyte for rechargeable Mg batteries. In Mg(TFSA) 2 /G3 electrolyte solutions (TFSA = bis(trifluoromethanesulfonyl)amide), we found from Raman spectroscopy that Mg 2+ ion is solvated with two G3 molecules to form [Mg(G3) 2 ] 2+ complexes. No direct coordination of TFSA − anion to Mg 2+ ion occurs in the solutions with the salt concentrations c Mg = 0−1.60 M. The geometries and interaction energies for the [Mg(G3) 2 ] 2+ were evaluated by DFT calculations and indicated that G3 molecules in the most stable complex act as a tridentate ligand, i.e., octahedral [Mg(tri-G3) 2 ] 2+ . However, the Raman spectra implies that [Mg(tri-G3) 2 ] 2+ coexists with [Mg(tetra-G3) (bi-G3)] 2+ in the solutions where tetra-G3 and bi-G3 are G3 molecules acting as tetra-and bidentate ligands, respectively, in the solvation sphere. The Walden plots indicated that the dissociativity (or ionicity) of Mg(TFSA) 2 in G3 solutions increases with increasing c Mg , which is opposite to conventional organic electrolyte solutions but is similar to the LiTFSA/glyme solutions. ■ INTRODUCTIONMagnesium (Mg), one of the s-block elements that can exist as a divalent cation Mg 2+ has attracted attention in battery chemistry because of its high volumetric capacity, high negative reduction potential, and low cost relative to lithium-based batteries. To establish a practical rechargeable Mg battery system, it is well-recognized that the development of electrode materials and electrolytes using nonaqueous solvents play a key role and thus are now required to improve battery performance. In the latter viewpoints, the design of electrolyte is important to control ionic conductivity, ion diffusion, and solvation/ desolvation of metal ion at the electrode/electrolyte interface. The solvation/desolvation process of Mg ion is related to the charge transfer kinetics, i.e., dissolution/deposition behavior of Mg metal at the electrode, which controls current density directly. It is well-known that using Grignard reagents (R− Mg−X; R = alkyl groups and X = halides such as Br and Cl) Mg can be reversibly deposited in ethereal solvents such as tetrahydrofuran (THF) to give a rechargeable Mg battery system. 1 Aurbach et al. also proposed organo-haloaluminate salts such as Mg(AlCl 3 R) 2 or Mg(AlCl 2 RR′) in THF as promising electrolytes showing reversible dissolution/deposition of Mg. 2−5 Except for such electrolytes containing organoMg complexes, there have been no reports on reversible dissolution/deposition system using electrolyte solutions of simple MgX salts (X = ClO 4 , BF 4 , CF 3 SO 3 , etc.) in conventional nonaqueous solvents (propylene carbonate, acetonitrile, N,N-dimethylformamide, etc.) similar to electrolytes for Li ion batteries. 6 Recently, a system using simple Mg salt with bis(trifluoromethanesulfonyl)amide (TFSA) anion, Mg(TFSA) 2 , in dimethoxy ethylene (glyme)-type solvents was reported as a promising electrolyte for rechargeable Mg b...
We describe the use of allogeneic human tendon as an intra-articular replacement for the anterior cruciate ligament. Depending on the type and degree of functional instability we recommend the addition, in some cases, of supplementary extra-articular procedures. We have reviewed 31 patients at least two years after operation and have found that 30 of them had been able to return to full sporting activities. The indications for operation and the techniques are discussed and the use of allogeneic tendon is recommended. 1 3 women with an average age of 25 years (range 18 to 46 years). The average time from the initial injury to the K. Shino, MD. DMSC.
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