Electrical determination of the valence-band discontinuity in HgTe-CdTe heterojunctions

Current-voltage behavior is studied experimentally in a Hg0.78Cd0.22Te-CdTe-Hg0.78Cd0.22Te heterostructure grown by molecular beam epitaxy. At temperatures above 160 K, energy-band diagrams suggest that the dominant low-bias current is thermionic hole emission across the CdTe barrier layer. This interpretation yields a direct determination of 390±75 meV for the HgTe-CdTe valence-band discontinuity at 300 K. Similar analyses of current-voltage data taken at 190–300 K suggest that the valence-band offset decreases at low temperatures in this heterojunction

Dynamic Kerr Effect and Spectral Weight Transfer in the Manganites

We perform pump-probe Kerr spectroscopy in the colossally magnetoresistive manganite Pr0.67Ca0.33MnO3. Kerr effects uncover surface magnetic dynamics undetected by established methods based on reflectivity and optical spectral weight transfer. Our findings indicate the connection between spin and charge dynamics in the manganites may be weaker than previously thought. Additionally, important differences between this system and conventional ferromagnetic metals manifest as long-lived, magneto-optical coupling transients, which may be generic to all manganites.Comment: 12 text pages, 4 figure

To Act and Learn: A Bakhtinian Exploration of Action Learning

This paper considers the work of the Russian social philosopher and cultural theorist, Mikhail Mikhailovich Bakhtin as a source of understanding for those involved in action learning. Drawing upon data gathered over two years during the evaluation of 20 action learning sets in the north of England, we will seek to work with the ideas of Bakhtin to consider their value for those involved in action learning. We consider key Bakhtin features such as Making Meaning, Participative Thinking, Theoreticism and Presence, Others and Outsideness, Voices and Carnival to highlight how Bakhtin's can enhance our understanding of the nature of action and learning

Network information and connected correlations

Entropy and information provide natural measures of correlation among elements in a network. We construct here the information theoretic analog of connected correlation functions: irreducible $N$--point correlation is measured by a decrease in entropy for the joint distribution of $N$ variables relative to the maximum entropy allowed by all the observed $N-1$ variable distributions. We calculate the ``connected information'' terms for several examples, and show that it also enables the decomposition of the information that is carried by a population of elements about an outside source.Comment: 4 pages, 3 figure

Developing transferable management skills through Action Learning

There has been increasing criticism of the relevance of the Master of Business Administration (MBA) in developing skills and competencies. Action learning, devised to address problem-solving in the workplace, offers a potential response to such criticism. This paper offers an insight into one university’s attempt to integrate action learning into the curriculum. Sixty-five part-time students were questioned at two points in their final year about their action learning experience and the enhancement of relevant skills and competencies. Results showed a mixed picture. Strong confirmation of the importance of selected skills and competencies contrasted with weaker agreement about the extent to which these were developed by action learning. There was, nonetheless, a firm belief in the positive impact on the learning process. The paper concludes that action learning is not a panacea but has an important role in a repertoire of educational approaches to develop relevant skills and competencies

Optical evidence for transient photoinduced magnetization in La\u3csub\u3e0.7\u3c/sub\u3eCa\u3csub\u3e0.3\u3c/sub\u3eMnO\u3csub\u3e3\u3c/sub\u3e

Pump-probe Kerr spectroscopy reveals evidence for transient photoinduced magnetization (PIM) near Tc in the colossally magnetoresistive manganite La0.7Ca0.3MnO3. For temperatures above Tc, the PIM signature reaches full strength at the field-driven magnetic phase transition, while below Tc it exhibits a magnetic activation threshold of ~0.5 T. We compare the temperature dependence of the effect with diffuse spin scattering previously measured with neutrons and discuss these findings in the context of phase separation near Tc

The effects of land use disturbance vary with trophic position in littoral cichlid fish communities from Lake Tanganyika

1. Impacts of anthropogenic disturbance are especially severe in freshwater ecosystems. In particular, land use disturbance can lead to increased levels of pollution, including elevated nutrient and sediment loads whose negative impacts range from the community to the individual level. However, few studies have investigated if these impacts are uniform across species represented by multiple trophic levels. To address this knowledge gap, we focused on Lake Tanganyika cichlid fishes, which comprise hundreds of species representing a wide range of feeding strategies. Cichlids are at their most diverse within the near‐shore environment; however, land use disturbance of this environment has led to decreasing diversity, particularly in herbivores. We therefore tested if there is a uniform effect of pollution across species and trophic groups within the hyper‐diverse rocky shore cichlid fish community. 2. We selected three sites with differing levels of human impact along the Tanzanian coastline and 10 cichlid species, comprising varying taxonomic and trophic groups, common to these sites. Nitrogen and carbon stable isotope values for 528 samples were generated and analysed using generalised linear mixed models. We also estimated stomach contents including sediment proportions. 3. Our study highlights that multiple sources of pollution are having differing effects across species within a diverse fish community. We found that nitrogen stable isotope values were significantly higher at the most disturbed (urbanised) site for benthic feeding species, whereas there was no difference in these isotopes between sites for the water column feeding trophic group. Stomach contents revealed that the elevated δ15N values were unlikely to have been caused by differences in diet between sites. However, at the most disturbed site, higher proportions of sediment were present in most herbivores, irrespective of foraging behaviour. 4. It is likely that anthropogenic nitrogen loading is the cause of higher nitrogen stable isotope values since there was no evidence of species shifting trophic levels between sites. Results support our previous study showing herbivore species to be most affected by human disturbance and make the link to pollution much more explicit. As lower diversity of consumers can negatively affect ecosystem processes such as stability, alleviating environmental impact through sewage treatment and afforestation programmes should continue to be a global priority for the conservation of aquatic ecosystems, as well as human health

Ecological equivalence: a realistic assumption for niche theory as a testable alternative to neutral theory

Hubbell's 2001 neutral theory unifies biodiversity and biogeography by modelling steady-state distributions of species richness and abundances across spatio-temporal scales. Accurate predictions have issued from its core premise that all species have identical vital rates. Yet no ecologist believes that species are identical in reality. Here I explain this paradox in terms of the ecological equivalence that species must achieve at their coexistence equilibrium, defined by zero net fitness for all regardless of intrinsic differences between them. I show that the distinction of realised from intrinsic vital rates is crucial to evaluating community resilience. An analysis of competitive interactions reveals how zero-sum patterns of abundance emerge for species with contrasting life-history traits as for identical species. I develop a stochastic model to simulate community assembly from a random drift of invasions sustaining the dynamics of recruitment following deaths and extinctions. Species are allocated identical intrinsic vital rates for neutral dynamics, or random intrinsic vital rates and competitive abilities for niche dynamics either on a continuous scale or between dominant-fugitive extremes. Resulting communities have steady-state distributions of the same type for more or less extremely differentiated species as for identical species. All produce negatively skewed log-normal distributions of species abundance, zero-sum relationships of total abundance to area, and Arrhenius relationships of species to area. Intrinsically identical species nevertheless support fewer total individuals, because their densities impact as strongly on each other as on themselves. Truly neutral communities have measurably lower abundance/area and higher species/abundance ratios. Neutral scenarios can be parameterized as null hypotheses for testing competitive release, which is a sure signal of niche dynamics. Ignoring the true strength of interactions between and within species risks a substantial misrepresentation of community resilience to habitat los