Large magnetoresistance and quantum oscillations in Sn0.05Pb0.95Te.

We have synthesized high-quality single crystals of SnxPb1-xTe and carried out detailed studies of the magnetotransport properties of one of the samples, Sn0.05Pb0.95Te. Longitudinal magnetoresistance increases almost linearly with increasing applied field (H) and reaches ∼310% atH= 13 T. At higher fields, both longitudinal and Hall resistance show clear Shubnikov de Haas oscillations. The oscillations are smooth and periodic, and there exists only one frequency,fα∼ 57 T. However, an additional frequency,fß∼ 69 T, appears as the angle between the field direction and the normal to the sample surface (θ) is increased. Bothfαandfßexhibitθ-dependence;fαdecreases whereasfßincreases gradually with increasingθ. The presence of two frequencies in Sn0.05Pb0.95Te indicates that there exist two Fermi surface pockets (αandßpockets). We have constructed the Landau-level fan plot and determined the Berry phase (δ) for theαpocket to beδ∼ 0.1. Thisδvalue is very close to the expected value of 0 for a topologically trivial system.

Cardiovascular adjustments and perceived exertion during exercise on the BAPS board.

The Biomechanical Ankle Platform System (BAPS) is widely used in medical rehabilitation; however, the cardiovascular demand and subjective acceptability of the BAPS rehabilitation exercise are presently not documented. The purpose of this study was to evaluate the pattern and magnitude of the cardiovascular adjustments and rating of perceived exertion (RPE) during an acute bout of exercise on the wobble board. Twenty healthy (mean age 24.2 +/- 2.9 years old) subjects exercised for 10 min each on the BAPS board on two different occasions. One test was performed using the small hemisphere board while the other test was performed with the large hemisphere board. The subjects' heart rate (HR), blood pressure (BP), cutaneous blood flow (BF), skin temperature (ST) at the ankle joint, local and overall RPE responses were monitored at specific time periods. Micro-circulation, skin temperature and heart rate were monitored with the LaserFlo Blood Perfusion Monitor, the Physitherm thermocouple and the Cardiotach recorder, respectively. The subjects' rating of perceived effort during exercise was obtained with a 15-point category scale. The result showed significant perturbation of the cardiovascular system during the BAPS exercise. Similarly, both local and overall RPE increased as the duration of exercise increased. The BF and RPE during the large hemisphere exercise session were significantly higher than the small hemisphere session. The subjects' subjective report following the exercise suggests the need for caution in the use of the BAPS board exercise for frail patients and also patients with lower extremity joint pathologies.