Investigation of phonon suppression by nanostructuring and doping in thermoelectric half Heusler materials

We live in the age when humanity finds itself on the edge of energy crisis, fossil fuels are consumed and our energy consumption rises every year. One solution would be to obtain energy from renewable sources and to minimize the losses of energy produced, e.g. reuse the waste heat. Thermoelectric materials can convert heat directly and reversibly into electricity and allow therefore to use waste thermal energy more efficiently. Their benefits include the absence of moving parts, quiet operation, reliability, durability, and the fact that they do not produce any polluting emissions, so we can use them in a wide range of applications and they are also attractive from an environmental point of view. Half Heusler alloys belong to one of the most promising thermoelectric materials composed of relatively non toxic and abundant elements, with highest ZT 1.5 at 700 K for Zr0,25Hf0,25Ti0,5Ni1Sn0,998Sb0,002 at. alloy. In our study we try to improve the thermoelectric performance of this alloy by doping it with semiconducting dispersion phase amp; 946; FeSi2, which should reduce the thermal conductivity of the origin alloy. Since thermal conductivity depends to large extent on the propagation of phonons we have investigated how the nanostructuring of the samples by means of ball milling and doping impact the phonon behavior. For this purpose we have conducted inelastic neutron scattering experiments using the time of flight spectrometer NEAT at Helmholtz Zentrum Berlin. In this paper are presented results of our study demonstrating the effect of phonon suppression by nanostructuring and doping in thermoelectric half Heusler alloys

β2-Adrenergic stimulation enhances Ca2+ release and contractile properties of skeletal muscles, and counteracts exercise-induced reductions in Na+-K+-ATPase Vmax in trained men

The aim of the present study was to examine the effect of β2-adrenergic stimulation on skeletal muscle contractile properties, sarcoplasmic reticulum (SR) rates of Ca2+ release and uptake, and Na+-K+-ATPase activity before and after fatiguing exercise in trained men. The study consisted of two experiments (EXP1, n = 10 males, EXP2, n = 20 males), where β2-adrenoceptor agonist (terbutaline) or placebo was randomly administered in double-blinded crossover designs. In EXP1, maximal voluntary isometric contraction (MVC) of m. quadriceps was measured, followed by exercise to fatigue at 120% of maximal oxygen uptake (V˙O2, max ). A muscle biopsy was taken after MVC (non-fatigue) and at time of fatigue. In EXP2, contractile properties of m. quadriceps were measured with electrical stimulations before (non-fatigue) and after two fatiguing 45 s sprints. Non-fatigued MVCs were 6 ± 3 and 6 ± 2% higher (P &amp;lt; 0.05) with terbutaline than placebo in EXP1 and EXP2, respectively. Furthermore, peak twitch force was 11 ± 7% higher (P &amp;lt; 0.01) with terbutaline than placebo at non-fatigue. After sprints, MVC declined (P &amp;lt; 0.05) to the same levels with terbutaline as placebo, whereas peak twitch force was lower (P &amp;lt; 0.05) and half-relaxation time was prolonged (P &amp;lt; 0.05) with terbutaline. Rates of SR Ca2+ release and uptake at 400 nm [Ca2+] were 15 ± 5 and 14 ± 5% (P &amp;lt; 0.05) higher, respectively, with terbutaline than placebo at non-fatigue, but declined (P &amp;lt; 0.05) to similar levels at time of fatigue. Na+-K+-ATPase activity was unaffected by terbutaline compared with placebo at non-fatigue, but terbutaline counteracted exercise-induced reductions in maximum rate of activity (Vmax) at time of fatigue. In conclusion, increased contractile force induced by β2-adrenergic stimulation is associated with enhanced rate of Ca2+ release in humans. While β2-adrenergic stimulation elicits positive inotropic and lusitropic effects on non-fatigued m. quadriceps, these effects are blunted when muscles fatigue.CODEN: JPHYA</p