Nine healthy men carried out head-down bed rest (BR) for 20 days. five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.
We concluded that blood flow to the nonworking limbs increases markedly in proportion to the work intensity. These results suggest that the conduit arteries in the nonworking limbs are exposed to increases in blood flow and shear stress during exercise.
A novel metallic and magnetic transition metal oxide Ag 2 NiO 2 is studied by means of resistivity, magnetic susceptibility, specific heat and X-ray diffraction. The crystal structure is characterized by alternating stacking of a Ni 3+ O 2 layer and a (Ag 2 ) + layer, the former realizing a spin-1/2 triangular lattice with e g orbital degeneracy and the latter providing itinerant electrons. It is found that the NiO 2 layer exhibits orbital ordering at T s = 260 K and antiferromagnetic spin ordering at T N = 56 K. Moreover, a moderately large mass enhancement is found for the itinerant electrons, suggesting a significant contribution from the nearly localized Ni 3d state to the Ag 5s state that forms a broad band. PACS number: 75.50-y, 75.30.Et, 72.80.GaFrustration on triangle-based lattices is one of key ingredients for quantum phenomena to be induced in various electron systems with spin, orbital and charge degrees of freedom. It suppresses classical long-range order (LRO) associated with these degrees of freedom and sometimes leads to a "liquid" ground state with finite entropy. 1 Another interesting issue emerging recently is to clarify the role of frustration on itinerant electrons in frustrated lattices. One would expect some influence especially for a strongly correlated electron system, where both charge and spin degrees of freedom may coexist marginally. A good example is found in a mixed valent vanadium spinel compound LiV 2 O 4 that exhibits unusual heavy-Fermion like behavior. 2, 3 It is suggested that orbital degeneracy survives due to frustration on the pyrochlore lattice and gives rise to a large mass enhancement of 3d electrons.LiNiO 2 was first assumed to be a candidate for the spin-1/2 triangular antiferromagnet, because it comprises Ni 3+ ions in the low-spin state (t 2g 6 e g 1 ) with an isotropic S = 1/2, arranged in a triangular lattice which stacks alternatingly with a nonmagnetic Li + layer. 4 However, later studies have revealed that a net magnetic interaction between neighboring Ni 3+ spins in LiNiO 2 is ferromagnetic (FM), not antiferromegnetic (AFM), and thus there is no frustration for spins. 5 In spite of this, LiNiO 2 still remains interesting because of the absence of a cooperative Jahn-Teller distortion that is expected for such a system with orbital degeneracy. 6 Experimental results on LiNiO 2 are rather controversial. It always suffers from nonstoichiometry: excess Ni ions replace Li ions, which gives rise to a local interlayer FM coupling that competes with an intrinsic AFM coupling. 5, 7 It is believed that ideal LiNiO 2 would be a quantum spin-orbital liquid without LRO, where frustration prevents orbital ordering as well as spin ordering in spite of dominant FM couplings. 8It is pointed out, alternatively, that the absence of LRO is due to the excess Ni ions and that ideal LiNiO 2 would be
The thickness, fascicle angles of pennation, and fascicle length of the vastus lateralis (VL) and medial gastrocnemius (MG) muscles in highly trained soccer players and swimmers of both genders were determined from ulrasonograms to investigate whether the fascicle arrangements of the lower limb muscles in the athletes could be related to the requirements of the events, i. e., intensive muscular activities in the water versus on the ground. In comparisons between the two events, the soccer players tended to show shorter fascicles and greater fascicle angles, and the swimmers thicker muscles and longer fascicles, especially in VL. In both events, the males showed thicker muscles and greater fascicle angles than the females. In both VL and MG, the thickness, fascicle length and fascicle angle were related to each other in a right-angled triangle model, and so, most of the event- and/or gender-related differences observed in the fascicle angle depended on the difference in muscle thickness relative to fascicle length. The present data cannot answer the question of whether the athletes had muscles suited to their respective sports prior to beginning their sports or whether the muscles adapted specifically to the competitive and/or training styles. However, it might be assumed that the lower limb muscles for swimmers are suitable to perform rapid, powerful kick movements during competitive swims by having greater thickness and longer fascicle, i. e., priorities in both force production and shortening velocity, but those for soccer players do not show architectural profiles which can be related to intensive activity on the ground, except that the thickness values exceed the normal range.
LaFe 0.5 Mn 0.5 O 3 solid solution films have been formed on SrTiO3 (111) substrates using a pulsed laser deposition technique and their magnetic properties have been examined. The films showed ferromagnetic (or ferromagnetic) behavior with a Curie temperature of 380 K and the saturation magnetization was estimated to be about 1.5μB per magnetic ion site (B site). The x-ray photoemission spectra indicated that this behavior was due to the partial ordering of magnetic ions (Fe and Mn ions) which is caused by the charge disproportion between Fe and Mn ions under the film formation conditions.
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