Field and pressure response of Yb compounds close to a quantum critical point

YbCu_5−x Al _x provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic field. Near to the critical concentration x _cr≈1.5 non-Fermi-liquid properties (NFL) are obvious, obeying hyperscaling. If magnetic order sets in for x>1.5, the application of moderate magnetic fields quenches order and again NFL features become evident. Hyperscaling in this case indicates strongly interacting spin fluctuations.     

EFFECTS OF PHASIC AND TONIC LIGHT INPUTS ON THE ORCADIAN ORGANIZATION OF THE SQUIRREL MONKEY

Abstract— The organization of the circadian timing system in Saimiri sciureus was probed using the phasic (abrupt transition) and tonic (continuous action) effects of light intensity. The behavior of the simultaneously monitored circadian rhythms of feeding behavior, colonic temperature, and urinary potassium excretion was studied in response to the phasic effects of (a) an abrupt 8-h phase delay in the light–dark (LD) cycle and (b) a series of non-24 h LD cycles ( T = 18 to 30 h). These studies demonstrated that the feeding and temperature rhythms were more tightly coupled to the light-dark cycle than was the rhythm of urinary potassium excretion. The tonic effects of constant levels of illumination confirmed this conclusion. In constant light, internal desynchronization spontaneously occurred in 25% of animals with the potassium rhythm exhibiting a period quite different from that of the feeding and colonic temperature rhythms. Thus, the response of the internal circadian timekeeping system to phasic and tonic light inputs shows that the system in this species comprises at least two potentially independent oscillators with differential light sensitivities.     

A laboratory comparison of two methods used to estimate the isotopic composition of soil delta13CO2 efflux at steady state

The stable isotopic composition of soil (13)CO(2) flux is important for monitoring soil biological and physical processes. While several methods exist to measure the isotopic composition of soil flux, we do not know how effective each method is at achieving this goal. To provide clear evidence of the accuracy of current measurement techniques we created a column filled with quartz sand through which a gas of known isotopic composition (-34.2 per thousand) and concentration (3,000 ppm) diffused for 7 h. We used a static chamber at equilibrium and a soil probe technique to test whether they could identify the isotopic signature of the known gas source. The static chamber is designed to identify the source gas isotopic composition when in equilibrium with the soil gas, and the soil probe method relies on a mixing model of samples withdrawn from three gas wells at different depths to identify the gas source. We sampled from ports installed along the side of the sand column to describe the isotopic and concentration gradient as well as to serve as a control for the soil probe. The soil probe produced similar isotopic and concentration values as the control ports, as well as Keeling intercepts. The static chamber at equilibrium did not identify the source gas but, when applied in a two end-member mixing model, did produce a similar Keeling intercept produced from the control ports. Neither of the methods was able to identify the source gas via the Keeling plot method probably because CO(2) profiles did not reach isotopic steady state. Our results showed that the static chamber at equilibrium should be used only with a Keeling plot approach and that the soil probe is able to provide estimates of uncertainty for the isotopic composition of soil gas as well as information pertinent to the soil profile.