Large Enhancement of Thermoelectric Efficiency Due to a Pressure-Induced Lifshitz Transition in SnSe.

The Lifshitz transition, a change in Fermi surface topology, is likely to greatly influence exotic correlated phenomena in solids, such as high-temperature superconductivity and complex magnetism. However, since the observation of Fermi surfaces is generally difficult in the strongly correlated systems, a direct link between the Lifshitz transition and quantum phenomena has been elusive so far. Here, we report a marked impact of the pressure-induced Lifshitz transition on thermoelectric performance for SnSe, a promising thermoelectric material without a strong electron correlation. By applying pressure up to 1.6 GPa, we have observed a large enhancement of the thermoelectric power factor by more than 100% over a wide temperature range (10-300 K). Furthermore, the high carrier mobility enables the detection of quantum oscillations of resistivity, revealing the emergence of new Fermi pockets at ∼0.86 GPa. The observed thermoelectric properties linked to the multivalley band structure are quantitatively reproduced by first-principles calculations, providing novel insight into designing the SnSe-related materials for potential valleytronic as well as thermoelectric applications.

Emergence of a diffusive metal state with no magnetic order near the Mott transition in frustrated pyrochlore-type molybdates.

The electron-correlation driven metal-insulator (Mott) transition in pyrocholore-type R2Mo2O7(R being rare-earth-metal ions) is accompanied by the change of the magnetic state from ferromagnetic to spin glass due to the competing double-exchange and superexchange interactions on the frustrated lattice. By application of high pressures on the compounds with Mott criticality, however, a new unique paramagnetic metal phase is observed to show up with nearly temperature-independent high resistivity close to the Ioffe-Regel limit. A possible non-Fermi-liquid character of this anomalously diffuse metallic state is argued in terms of the extended double-exchange model with the magnetically frustrated local S=1/2 spins.

Anomalous nernst effects in pyrochlore molybdates with spin chirality.

The transverse thermoelectric (Nernst) effect on pyrochlore molybdates is investigated experimentally. In Nd(2)Mo(2)O(7) and Sm(2)Mo(2)O(7) with the spin chirality, the Nernst signal, which mostly arises from the transverse heat current (or equivalently the transverse Peltier coefficient alpha(xy)), shows a low-temperature (20-30 K) positive extremum, whereas it is absent in (Gd(0.95)Ca(0.05))(2)Mo(2)O(7) with no single-spin anisotropy of the rare-earth ion and hence with no spin chirality. The correlation between the Hall conductivity sigma(xy) and alpha(xy) in Nd(2)Mo(2)O(7) also indicates the spin chirality plays a significant role in the spontaneous (anomalous) Nernst effect.

Scaling of anomalous hall resistivity in Nd2(Mo(1-x)Nb(x))2O7 with spin chirality.

We have investigated scaling of anomalous Hall resistivity with longitudinal resistivity (rho(xx)) in pyrochlore type Nd2(Mo(1-x)Nb(x))2O7 with spin chirality. Scattering rate of the conduction electron on the Mo sublattice can be varied with x from band transport to polaron hopping, while keeping the two-in-two-out structure of the Nd moments intact. The anomalous part of the Hall resistivity arising from the Mo spin chirality (rho(H)(chi)) shows a clear scaling behavior with rho(xx) (rho(H)(chi) proportional to rho(xx)0.39), in accord with a recent theoretical result based on the Berry phase mechanism in the hopping conduction regime.

Nature of the transition between a ferromagnetic metal and a spin-glass insulator in pyrochlore molybdates.

The metal-insulator transition has been investigated for pyrochlore molybdates R(2)Mo(2)O(7) with nonmagnetic rare-earth ions R. The dynamical scaling analysis of ac susceptibility reveals that the geometrical frustration causes the atomic spin-glass state. The reentrant spin-glass phase exists below the ferromagnetic transition. The electronic specific heat is enhanced as compared to the band calculation result, perhaps due to the orbital fluctuation in the half-metallic ferromagnetic state. The large specific heat is rather reduced upon the transition, likely because the short-range antiferromagnetic fluctuation shrinks the Fermi surface.

Mott-Anderson transition controlled by a magnetic field in pyrochlore molybdate.

The pyrochlore molybdate Gd2MO2O7 locates near the phase boundary between the ferromagnetic-metallic and the spin-glass insulating state. This metal-insulator transition is governed on a large energy scale by the electron-correlation effect, while the geometrical frustration causes the random potential. The magnetic field can tune the randomness of the potential and control, under a suitable pressure, the continuous Mott-Anderson transition precisely. The critical exponent (mu = 1.04 +/- 0.1) of the Mott-Anderson transition has been determined for this ferromagnetic orbital-degenerate electron system.

The fate of ACTH released from rat anterior pituitary into the incubation medium in vitro: enzymatic degradation and acid activation.

The bioactivity of ACTH released from isolated rat anterior pituitary glands into the incubation medium was determined. After the pituitaries were removed, ACTH activity in the medium decreased exponentially during further incubation at 37degreesC. The loss of ACTH activity was temperature- and pH-dependent and inhibited both by protease inhibitor (trasylol) and by preheating. Crude tissue extracts from median eminence, cerebral cortex and liver similarly inhibited the loss of ACTH activity. These results indicate that ACTH released into the medium may be destroyed by proteolytic enzyme(s) from the rat anterior pituitary. ACTH activity in the incubation medium was increased promptly by acidification of the medium to pH 1.5-2.5 with HC1, and reduced to the initial level by NaOH reneutralization of the medium (pH 6.8-7.8). These phenomena were not observed after the incubation medium had been heated at 100degreesC for 5 min.

Relative potency in acute and chronic suppressive effects of prednisolone and betamethasone on the hypothalamic-pituitary-adrenal axis in man.

The relative potency in the hypothalamic-pituitary-adrenal (HPA) suppression of both prednisolone and betamethasone was examined in an acute study with normal volunteers and in a chronic study with glucocorticoid-treated patients. Circadian rhythm of plasma cortisol was studied after a single dose administration of 5 to 30 mg prednisolone or 0.5 to 3.0 mg betamethasone at 8:00 hr. Morning-rise of plasma cortisol occurred on the morning after the administration of 30 mg or less prednisolone but no morning rise was noted after the administration of 1.0 mg or more betamethasone. Plasma ACTH was slightly elevated on the morning after 30 mg prednisolone administration but showed low levels throughout the night after 3.0 mg betamethasone administration. Plasma cortisol responsiveness to ACTH was examined in patients before and during therapy with either prednisolone or betamethasone. The basal cortisol level was not suppressed and the responsiveness to ACTH remained nearly normal during long-term 5 mg prednisolone therapy, but these were completely suppressed during long-term 5 mg betamethasone therapy. The responsiveness to ACTH was nearly normal in patients receiving alternate-day therapy with prednisolone in such large doses as 50 or 60 mg every other day, but was completely suppressed in patients receiving 1.0 mg betamethasone every other day. The relative potency of betamethasone in acute and chronic suppressive effects on the HPA system seems to be much stronger than that of prednisolone in equivalent doses with comparable anti-inflammatory effects. It is also suggested that the alternate-day therapy with such long-acting steroids as betamethasone are useless in preventing HPA suppression.

Charge dynamics near the electron-correlation induced metal-insulator transition in pyrochlore-type molybdates.

The systematics of the bandwidth controlled metal-insulator transition (MIT) are investigated for R2Mo2O7 (R=Nd, Sm, Gd, Dy, and Ho) by measurements of dc and optical conductivity. The substantial role of electron correlation in driving the MIT is verified. With changing the R ionic radius (r) or equivalently the one-electron bandwidth, the T=0 K MIT occurs at rc approximately r(R=Gd). The T=0 K gap continuously vanishes as Delta proportional, variant(rc-r), while at the metallic side the decrease of Drude weight is followed towards rc. A high-temperature incoherent state is approached through crossover regions both from the metallic and the insulating state.

[Effect of biogenic amines on rat anterior pituitary cyclic AMP].

The effects of biogenic amines on the formation of adenosine-3',5' monophosphate (cAMP) in the anterior pituitary of rats were investigated. Pituitary halves were preincubated in a Krebs-Ringer bicarbonate buffer (pH 7.4) containing theophylline (10(-2)M) at 37 degrees C for 30 minutes and incubated in a fresh buffer for 15 minutes after the addition of test substances. Noradrenaline at 4 X 10(-4)M and serotonin at 3.3 X 10(-4)M were effective in elevating cAMP, but dopamine at 2 X 20(-4)M was ineffective. The beta adrenergic blocking agent, propranolol, effectively antagonized the cAMP response to noradrenaline, but the alpha adrenergic blocking agent, phentolamine, did not. The serotonin antagonist, methysergide, remarkably antagonized the cAMP response to serotonin, but the alpha and beta adrenergic agents did not.