On the Spin Gap Phase of Strongly-Correlated Electrons

We discuss the possible existence of a spin-gap phase in the low-doping regime of strongly-correlated two-dimensional electrons within the gauge field description of the t-J model. The spin-gap phase was recently shown by Ubbens and Lee to be destroyed by gauge field quantum fluctuations for a single-layer 2D system in the absence of disorder and for a full gap. We show that the same conclusion applies both in the dirty limit and for the case of a gapless spinon condensate.Comment: 7 pages, uuencoded Postscript, including 1 figur

Body growth, mitochondrial enzymatic capacities and aspects of the antioxidant system and redox balance under calorie restriction in young turbot (Scophthalmus maximus, L.).

Caloric reduction (cr) without undernutrition has been found to enhance stress resistance and life span in endotherms and ectotherms. We investigated the effect of 30% reduction in food offering on growth, aerobic capacities and oxidative stress parameters in young turbot (Scophthalmus maximus, L.).No differences in body weight, length and hepatosomatic index between the ad libitum fed (AL) and the calorie reduced (CR) group occurred after 55 days of diet application. Of the mitochondrial marker enzymes, only citrate synthase activity in liver was reduced under CR, whereas muscle CS activity and cytochrome oxidase activity in both tissues remained the same in both feeding groups. The concentration of reduced glutathione increased significantly during feeding in muscle of CR fish, resulting in a more reduced glutathione redox ratio (GSH/GSSG) compared to AL fish muscle. TBARS (lipid peroxidation) but not protein carbonyl content (protein oxidation) was significantly reduced in CR fish muscle. Liver oxidative stress parameters did not vary significantly between experimental feeding groups.We conclude that 30% calorie reduction over 8 weeks has no adverse effect on young turbot. On the contrary, cr supports a reduced tissue oxidation state and reduces accumulation of lipid peroxidation products in muscle at sustained muscular aerobic capacity

What happens if density increases? Conservation implications of population influx into refuges

Sudden catastrophic events like fires, hurricanes, tsunamis, landslides and deforestation increase population densities in habitat fragments, as fleeing animals encroach into these refuges. Such sudden overcrowding will trigger transient fluctuations in population size in the refuges, which may expose refuge populations to an increased risk of extinction. Until recently, detailed information about the operation of density dependence in stage-structured populations, and tools for quantifying the effects of transient dynamics, have not been available, so that exploring the extinction risk of such transient fluctuations has been intractable. Here, we use such recently developed tools to show that extinction triggered by overcrowding can threaten populations in refuges. Apart from situations where density dependence acts on survival, our results indicate that short-lived species may be more at risk than longer-lived species. Because dynamics in local populations may be critical for the preservation of metapopulations and rare species, we argue that this aspect warrants further attention from conservation biologists. © 2007 The Zoological Society of London