A High-Temperature Electrical Conduction Mechanism in the Lower Mantle Phase (Mg,Fe)1-xO

Measurements of electrical conductivity at high pressure and temperature were taken on the lower mantle phase magnesiowustite with varying Fe3+ content. Although previous measurements at atmospheric pressure suggest Fe2+-Fe3+ hopping (small polaron) as the dominant conductivity mechanism, the present experiments show a change in charge transport mechanism with temperature. The lower temperature measurements are consistent with small polaron conduction, but at higher temperatures, which are more applicable to the lower mantle, a large polaron mechanism is suggested. Because these mechanisms have different temperature and compositional dependencies, this transition has important implications for extrapolation to mantle conditions.     

Evidence of indirect impacts of introduced trout on native amphibians via facilitation of a shared predator

Hyperpredation occurs when non-native prey facilitate invasive predators, which then suppress native prey. Direct impacts of introduced fish on amphibians are well studied, but the role of fish in supporting shared predators has not been considered. We present evidence for indirect effects of trout on amphibians through snake predation. Analyses of the diet, distribution and density of the Pacific coast aquatic garter snake (Thamnophis atratus) relative to the sympatric common garter snake (Thamnophis sirtalis) in the Klamath Mountains of California suggest that trout introductions facilitated expansion of T. atratus by providing alternative prey. T. atratus diet included trout and amphibians whereas T. sirtalis preyed solely upon amphibians. The distribution and density of T. atratus matched that of introduced trout instead of native amphibians. Populations of T. atratus could reach high densities in the absence of high densities of amphibians. When the snakes opportunistically prey upon amphibians whose numbers are already directly impacted by trout, they can cause significant additional declines. When T. atratus was present in lake basins, native Cascades frogs (Rana cascadae) were rarer than in basins without T. atratus. This case differs from other hyperpredation studies because the two prey species also interact via intraguild predation. Given the worldwide practice of stocking fish into aquatic habitats, it is important to understand the consequences of the practice on food-web structure and ecosystem functioning. Bottom-up impacts of introduced predators should be considered as well as top-down so that managers can incorporate the range of ecosystem-level effects into conservation goals and decisions.     

Unitary control in quantum ensembles: maximizing signal intensity in coherent spectroscopy

Experiments in coherent magnetic resonance, microwave, and optical spectroscopy control quantum-mechanical ensembles by guiding them from initial states toward target states by unitary transformation. Often, the coherences detected as signals are represented by a non-Hermitian operator. Hence, spectroscopic experiments, such as those used in nuclear magnetic resonance, correspond to unitary transformations between operators that in general are not Hermitian. A gradient-based systematic procedure for optimizing these transformations is described that finds the largest projection of a transformed initial operator onto the target operator and, thus, the maximum spectroscopic signal. This method can also be used in applied mathematics and control theory.     

Ultrasonographic Examination of the Scrotal Content in the Rabbit

This study was performed to describe a practical technique for ultrasound examination of the scrotal content of the rabbit. The scrotal content of normal rabbits and those with induced lesions (i.e. needle biopsy of the testis and epididymal ligation) were viewed using a portable scanner connected to a 5 or 7.5 MHz real time, B-mode linear array transducer. The effect of frequency (5 and 7.5 MHz), pad material placed under the testicle (rubber, plastic and carton) and the presence of a water sack between the probe and organ were examined to optimize the technique. The best image quality was obtained using a 5-MHz probe when the testicle was fixed on a rubber pad and covered by a water sack. Testicular parenchyma was imaged as homogeneous and moderately echoic. Caput and cauda epididymis were identified as homogeneous and less echoic compared with the testis parenchyma. Variations in the testicular echotexture that occur secondarily to epididymal ligation and testis biopsy could be screened readily. In conclusion, real-time ultrasonography, performed as described in this study, may provide a valuable tool to screen scrotal contents and to identify certain pathological conditions that affect fertility in the rabbit.     

STUDIES ON THE ROOT DEVELOPMENT OF HERBAGE PLANTS

Herbage, stubble and root weights were recorded for thirteen months on various leys subjected to two treatments differing in frequency of cutting.
The root-weight per unit area of a ryegrass/white-clover ley was not affected by the frequency of cutting, but the less frequently cut plots had fewer tillers per unit area; the root- and stubble-weight per tiller was, therefore, higher on the less frequently cut plots, On a cocksfoot ley the root-weight was not affected by the cutting treatment, but in late summer and early autumn the stubble-weight was considerably higher on the less frequently cut plots.
When cocksfoot was grown in rows 2 feet apart, the more frequent cutting decreased both the root- and stubble-weight.
On grass leys root-weights were heaviest in the summer and thereafter decreased until the following spring.
The root-weight of lucerne decreased from May to July, increased to a maximum in December and then decreased in weight. The changes in root-weight under lucerne leys were mainly due to changes in the weight of the tap-roots.
The vertical distribution of roots was recorded, and, in the case of the cocksfoot in rows, the lateral distribution of roots is also given.     

STUDIES ON THE ROOT DEVELOPMENT OF HERBAGE PLANTS

Two cutting treatments were applied to a cocksfoot sward, and the changes in fructosan and soluble–sugar contents of the roots, stubble and herbage were studied over a complete year.
Both the soluble-sugar and fructosan contents of roots were at a low level throughout the experiment. The total soluble carbohydrate in the roots never exceeded 4%. It is concluded that cocksfoot roots are not important storage regions for soluble carbohydrates.
The total soluble carbohydrate in herbage varied with season and reached a maximum of 10%. It was not affected by cuuing treatment.
In stubble the total stubble-carbohydrate content fluctuated markedly with season and reached a maximum of 18% in October; it was generally higher on the infrequently-cut swards than on those cut frequently. The soluble-sugar content was small and changed little with season or cutting treatment; the fructosan content, however, varied from 2 to 16–6% and accounted for most of the changes in the soluble-carbohydrate content. Stubble is apparently the major storage region for soluble carbohydrates in cocksfoot.
Under sward conditions, the quantity of soluble carbohydrates in the stubble of cocksfoot may have a positive effect on the herhage growth immediately after winter defoliation. However, when swards are actively growing in spring, other factors, such as tiller size and number, may be equally important in determining the amount of herbage recovery growth.