Supercurrent rectification and magnetochiral effects in symmetric Josephson junctions.

Transport is non-reciprocal when not only the sign, but also the absolute value of the current depends on the polarity of the applied voltage. It requires simultaneously broken inversion and time-reversal symmetries, for example, by an interplay of spin-orbit coupling and magnetic field. Hitherto, observation of nonreciprocity was tied to resistivity, and dissipationless non-reciprocal circuit elements were elusive. Here we engineer fully superconducting non-reciprocal devices based on highly transparent Josephson junctions fabricated on InAs quantum wells. We demonstrate supercurrent rectification far below the transition temperature. By measuring Josephson inductance, we can link the non-reciprocal supercurrent to an asymmetry of the current-phase relation, and directly derive the supercurrent magnetochiral anisotropy coefficient. A semiquantitative model explains well the main features of our experimental data. Non-reciprocal Josephson junctions have the potential to become for superconducting circuits what pn junctions are for traditional electronics, enabling new non-dissipative circuit elements.

Spin Relaxation in s-Wave Superconductors in the Presence of Resonant Spin-Flip Scatterers.

Employing analytical methods and quantum transport simulations we investigate the relaxation of quasiparticle spins in graphene proximitized by an s-wave superconductor in the presence of resonant magnetic and spin-orbit active impurities. Off resonance, the relaxation increases with decreasing temperature when electrons scatter off magnetic impurities-the Hebel-Slichter effect-and decreases when impurities have spin-orbit coupling. This distinct temperature dependence (not present in the normal state) uniquely discriminates between the two scattering mechanisms. However, we show that the Hebel-Slichter picture breaks down at resonances. The emergence of Yu-Shiba-Rusinov bound states within the superconducting gap redistributes the spectral weight away from magnetic resonances. The result is opposite to the Hebel-Slichter expectation: the spin relaxation decreases with decreasing temperature. Our findings hold for generic s-wave superconductors with resonant magnetic impurities, but also, as we show, for resonant magnetic Josephson junctions.

The effects of short-term exercise training on peak-torque are time- and fiber-type dependent.

We examined the susceptibility of fast and slow twitch muscle fibers in the quadriceps muscle to eccentric exercise-induced muscle damage. Nine healthy men (age: 22.5 ± 1.6 years) performed maximal eccentric quadriceps contractions at 120°·s-1 over a 120° of knee joint range of motion for 6 consecutive days. Biopsies were taken from the vastus lateralis muscle before repeated bouts of eccentric exercise on the third and seventh day. Immunohistochemical procedures were used to determine fiber composition and fibronectin activity. Creatine kinase (CK) and lactate dehydrogenase (LDH) were determined in serum. Average torque was calculated in each day for each subject. Relative to baseline, average torque decreased 37.4% till day 3 and increased 43.0% from the day 3 to day 6 (p < 0.001). Creatine kinase and LDH were 70.6 and 1.5 times higher on day 3 and 75.5 and 1.4 times higher on day 6. Fibronectin was found in fast fibers in subjects with high CK level on day 3 and 7 after exercise, but on day 7, fibronectin seemed in both slow and fast fibers except in muscles of 2 subjects with high fast fiber percentage. Peak torque and muscle fiber-type composition measured at baseline showed a strong positive association on day 3 (r = 0.76, p < 0.02) and strong negative association during recovery between day 3 and day 6 (r = -0.76, p < 0.02), and day 1 and day 6 (r = 0.84, p < 0.001). We conclude that the damage of fast fibers preceded the damage of slow fibers, and muscles with slow fiber dominance were more susceptible to repeated bouts of eccentric exercise than fast fiber dominance muscles. The data suggest that the responses to repeated bouts of eccentric exercise are fiber-type-dependent in the quadriceps muscle, which can be the basis for the design of individualized strength training protocols.

Mechanical, biochemical, and electromyographic responses to short-term eccentric-concentric knee extensor training in humans.

This study examined the effects of short-term eccentric-concentric knee extensor training on mechanical and biochemical variables, myoelectric activity, and muscle soreness. Seventeen men were assigned to either experimental (E, n = 10) or control group (C, n = 7). Group E performed 90 maximal isokinetic eccentric-concentric knee extensor contractions on each of 3 consecutive days (Tr1-Tr3) followed by 1-day rest, and then on 4 more consecutive days (Tr4-Tr7). Peak eccentric torque of each contraction during the training was recorded and averaged for each session (MTr). Maximal isometric torque (M0), eccentric torque (M(ecc)), integrated electromyography (iEMG), plasma creatine kinase (CK), and lactate dehydrogenase (LDH) activities were measured before, immediately, 24, 48, and 72 hours after Tr1, at 1 and 3 days after Tr7. Group C did not train but performed all exercise tests; CK and LDH were measured at 3 time points only. Acutely, M0 and M(ecc) decreased and CK, LDH, and soreness increased more in E than in C 24 hours after Tr1. Chronically, MTr and M0 increased more in E than C by Tr7 and CK, LDH, and muscle soreness gradually decreased by Tr7 whereas iEMG increased more in E than in C after Tr3 through Tr7. High-intensity short-term eccentric-concentric knee extensor exercise training produced immediate reductions in maximal voluntary force. Most likely neural adaptations contributed to rapid recovery and strength adaptations because maximal voluntary force increased by the end of the training protocol in previously trained healthy adults.

Impact of repeated bouts of eccentric exercise on myogenic gene expression.

Evidence indicates that repeated-bouts of eccentric exercise (EE) do not exacerbate the extent of muscle damage indices, as compared to a single-bout. We hypothesized that molecular adaptations, under repeated-bouts of EE, would include suppression of muscle repair inhibitory factors such as myostatin and up-regulation of muscle repair positive regulatory factors such as myogenic regulatory factors (MRFs). Fifteen males were recruited for this study. The exercise group (n=9) successfully completed six sets of 15 reps of maximum voluntary eccentric contractions, for six consecutive days, using a dynamometer (Multicont-II). Blood and muscle biopsy samples were obtained from each subject 1 week prior to exercise, 2 days post the first training session, and 24 h after the last training session. Gene expression levels were determined using real-time RT-PCR. Blood samples were analyzed for creatine kinase (CK) and lactate-dehydrogenase (LDH) activity. Repeated-bouts of EE induced a large down-regulation of myostatin mRNA (-73%) which persisted throughout the study. The responses of MRFs were mild. At day 3 only myogenin increased significantly (1.9 fold) while MyoD decreased by 45%. Surprisingly, at day 7, despite the presence of muscle damage indices, all MRFs returned to the pre-exercise levels. The results of the present study showed that repeated-bouts of EE, for six consecutive days, dramatically decreased Myostatin mRNA expression but impaired the expression patterns of MRFs such that, with the exception of myogenin that showed a moderate non-sustained increase, MyoD and MYf5 response was minimal.

[Increase of muscle mass and strength with hormones and other drugs, combined with physical training]. / Izomero, izomtömeg növelése hormonokkal és egyéb szerekkel, edzéssel társítva.

Increasing muscle mass and strength is the aim of some body builders and sportsmen, and is a therapeutic target in hormonal deficiencies, as well as in many clinical situations, when muscle devastation is a life-limiting factor. Human growth hormone, insulin-like growth factor, anabolic-androgen steroids and regulating proteins influencing muscle development and differentiation are used also for delaying the aging processes. Some of the practices are hailed by several myths, mainly because doping cases in certain competitive sports. Physiology, and therapeutic experiences with these substances are reviewed with special reference to physical exercise and to some frail conditions.