bluuebunny/crossref_metadata_2025 huggingface dataset:
Contrasting herbivory patterns and leaf fluctuating asymmetry inHeliocarpus pallidusbetween different habitat types within a Mexican tropical dry forest
Authors: Cuevas-Reyes Pablo , Oyama Ken , González-Rodríguez Antonio , Fernandes G. Wilson , Mendoza-Cuenca Luis
Published: May 2011

Leaf fluctuating asymmetry (FA) is considered an important indicator of environmentally induced stress in plants, but the relationship between herbivory and FA levels is not clear. In this study we compared leaf size and shape, leaf area consumed by herbivorous insects, and FA levels between individuals ofHeliocarpus pallidus(Tiliaceae) from two adjacent and contrasting habitat types (deciduous and riparian) in the Chamela–Cuixmala tropical dry-forest biosphere reserve. Ten individuals ofH. palliduswere collected in each habitat type. Leaf shape was assessed using geometric morphometric techniques. Results indicated statistically significant differences in leaf shape between individuals from the two habitat types. In individuals from the riparian habitat leaf area (mean = 42.3 ± 1.2 cm2), herbivory levels (mean = 25.5% ± 1.8%) and FA levels (mean = 0.38 ± 0.04 cm) were significantly higher than in individuals from the deciduous habitat (17.2 ± 3.5 cm2; 9.6% ± 1.0% and 0.18 ± 0.04 cm, respectively). Within habitats, significant correlations were found between total leaf area and percentage leaf area removed by insects (R2= 0.92 in riparian habitats,R2= 0.9 in deciduous habitats), and between percentage leaf area removed and FA (R2= 0.70 in riparian habitats,R2= 0.79 in deciduous habitats). As has been suggested for other plant species, it is possible that the more favourable conditions in the riparian habitat enhance leaf growth, resulting in higher FA. Also, individuals in this habitat might be characterized by lower chemical defence and/or higher nutritional quality, which would explain the higher herbivory levels.
Successful germination of seeds following passage through orang-utan guts
Authors: Nielsen Nynne H. , Jacobsen Magnus W. , Graham Laura L. L. B. , Morrogh-Bernard Helen C. , D'Arcy Laura J. , Harrison Mark E.
Published: May 2011

Orang-utans (Pongo spp.) are primarily frugivorous (Morrogh-Bernard et al. 2009) and are often regarded as important seed dispersers (Corlett 1998). In Tanjung Puting, Borneo, Galdikas (1982) found intact seeds in 94% of faecal samples, with a median 111 seeds per defecation; and in Ketambe, Sumatra, Rijksen (1978) found seeds in 44% of faecal samples. Furthermore, orang-utans have large day ranges (e.g. mean = 968 m, range = 280–2834 m across adults in Sabangau; Harrison 2009) and slow passage rates of digesta through the gut (Caton et al. 1999), and, hence, may disperse seeds far from parent trees. Many seeds are also spat out or discarded at distances up to 75 m from parent trees (Galdikas 1982).
Interactions between large herbivores and litter removal by termites across a rainfall gradient in a South African savanna
Authors: Buitenwerf Robert , Stevens Nicola , Gosling Cleo M. , Anderson T. Michael , Olff Han
Published: May 2011

Litter-feeding termites influence key aspects of the structure and functioning of semi-arid ecosystems around the world by altering nutrient and material fluxes, affecting primary production, foodweb dynamics and modifying vegetation composition. Understanding these complex effects depends on quantifying spatial heterogeneity in termite foraging activities, yet such information is scarce for semi-arid savannas. Here, the amount of litter that was removed from 800 litterbags in eight plots (100 litterbags per plot) was measured in Hluhluwe–iMfolozi Park (HiP) South Africa. These data were used to quantify variation in litter removal at two spatial scales: the local scale (within 450-m2 plots) and the landscape scale (among sites separated by 8–25 km). Subsequently, we attempted to understand the possible determinants of termites’ foraging patterns by testing various ecological correlates, such as plant biomass and bare ground at small scales and rainfall and fences that excluded large mammalian herbivores at larger scales. No strong predictors for heterogeneity in termite foraging intensity were found at the local scale. At the landscape scale termite consumption depended on an interaction between rainfall and the presence of large mammalian herbivores: litter removal by termites was greater in the presence of large herbivores at the drier sites but lower in the presence of large herbivores at the wetter sites. The effect of herbivores on termite foraging intensity may indicate a switch between termites and large herbivore facilitation and competition across a productivity gradient. In general, litter removal decreased with increasing mean annual rainfall, which is in contrast to current understanding of termite consumption across rainfall and productivity gradients. These results generate novel insights into termite ecology and interactions among consumers of vastly different body sizes across spatial scales.
Woody plant seedling distribution under invasive Lantana camara thickets in a dry-forest plot in Mudumalai, southern India
Authors: Ramaswami Geetha , Sukumar R.
Published: May 2011

Lantana camara, a shrub of Central and South American origin, has become invasive across dry forests worldwide. The effect of the thicket-forming habit of L. camara as a dispersal and recruitment barrier in a community of native woody seedlings was examined in a 50-ha permanent plot located in the seasonally dry forest of Mudumalai, southern India. Sixty 100-m2 plots were enumerated for native woody seedlings between 10–100 cm in height. Of these, 30 plots had no L. camara thickets, while the other 30 had dense thickets. The frequency of occurrence and abundance of seedlings were modelled as a function of dispersal mode (mammal, bird or mechanical) and affinities to forest habitats (dry forest, moist forest or ubiquitous) as well as presence or absence of dense L. camara thickets. Furthermore, frequency of occurrence and abundance of individual species were also compared between thickets and no L. camara. At the community level, L. camara density, dispersal mode and forest habitat affinities of species determined both frequency of occurrence and abundance of seedlings, with the abundance of dry-forest mammal-dispersed species and ubiquitous mechanically dispersed species being significantly lower under L. camara thickets. Phyllanthus emblica and Kydia calycina were found to be significantly less abundant under L. camara, whereas most other species were not affected by the presence of thickets. It was inferred that, by affecting the establishment of native tree seedlings, L. camara thickets could eventually alter the community composition of such forests.
Asymmetrical legitimate pollination in distylous Palicourea demissa (Rubiaceae): the role of nectar production and pollinator visitation
Authors: Valois-Cuesta Hamleth , Soriano Pascual J. , Ornelas Juan Francisco
Published: May 2011

We investigated morph differences in attributes that contribute to rewarding floral visitors of the distylous shrub Palicourea demissa at La Mucuy cloud forest in Venezuela. In both morphs, we measured nectar production from flowers subjected to repeated removals at 2-h intervals (10 plants per morph) and flowers that accumulated nectar for 24 h (10 plants per morph). In both cases, floral visitors were excluded. In addition, we quantified nectar availability (30 plants per morph), floral visitation (10–12 plants per morph) and legitimate pollination (30 plants per morph) throughout the day. We explored morph differences in the variables mentioned above using analyses of variance, and the effects of nectar variation on floral visitation and legitimate pollination using regression models. We observed 1205 floral visits, grouped into six hummingbird (94.7%) and three insect species (5.3%), across observations (264 h). Coeligena torquata was the most frequent floral visitor (34%) in both morphs (1.4–1.7 visits per plant h−1). Nectar production and availability, and visitation rate were similar between morphs. Visitation rate and legitimate pollen deposition increased with the nectar production in both morphs, but levels of legitimate pollination were higher on short-styled flowers than long-styled flowers. These results show that short-styled and long-styled flowers reward floral visitors equally, but frequency and foraging behaviour of long-billed pollinators can promote asymmetrical legitimate pollination.
Pollinators, pollination efficiency and fruiting success in a wild nutmeg, Myristica dactyloides
Authors: Sharma Manju V. , Shivanna Kundaranahalli R.
Published: May 2011

We investigated the pollinator assemblage in Myristica dactyloides, a dioecious tree species occupying the intermediate canopy stratum of the mid- and high-elevation wet evergreen forests and endemic to Sri Lanka and the Western Ghats of India. We surveyed two populations and, in one of them, marked four male and three female trees for observations on floral display and insect foraging, and two female trees for experimental pollination. Yellow sticky traps were used to sample insects in the canopy during the flowering season of December 2007 in addition to direct observations of insect activity in 2006. Myristicaceae members from other tropical areas have been reported to be specialized to beetle pollination, but our observations provide evidence of a generalist pollination system in M. dactyloides, composed of small, diverse insects: thysanopterans (thrips), coleopterans (beetles), halictid bees and dipterans (syrphid and phorid flies). Quantifying floral display, we found that female inflorescences were smaller, offered no reward and attracted significantly fewer pollinators in comparison to male inflorescences. Fruit set was low and could be attributed to a 29% flower abscission and abortion of young fruits, but a reasonably high natural pollination efficiency combined with pollination experiments established that there was no pollination limitation in the study population.
Editorial: On Censorship, Political Correctness, the Diagnostic and Community Building
Authors: ASTON ELAINE
Published: May 2011

‘Silent Voices/Forbidden Lives: Censorship and Performance’ was the topic of IFTR's annual conference held in Lisbon, Portugal, in July 2009. Introducing the theme of the conference, the organizers signalled the importance of censorship for Portugal and other countries with histories of governmental dictatorship, given the ways in which this has made an impact or left its mark on the cultural, social and political fabric of the nation. The first two articles in this issue, by Jean Graham-Jones and Paul Rae, arose out of papers presented at the Lisbon conference. Both authors open up the censorship debate to argue for more subtle accounts of how the term is conceptualized. In brief, both are mindful of the cautionary note sounded in an earlier TRI article on ‘the limits of censorship’ by Janelle Reinelt where she writes, ‘“Censorship” has become a common-sense catchword; since everyone knows what it means, merely to name it is to proclaim it.’
Freedom of Repression
Authors: RAE PAUL
Published: May 2011

Too programmatic an opposition to censorship fails to account for the nuanced justifications and popular support that underwrite some of the world's most refined censorship regimes. In this article, I argue that in order to do so, we need to place freedom, repression, regulation, expression and productivity in a more dynamic relationship than conventional critics of censorship are generally willing to entertain. By way of example, I examine theatre censorship in Singapore. The South East Asian city state inherited draconian colonial-era censorship regulations from the British, which it variously amends, rescinds and refines on a regular basis through a combination of negotiation, government review and, increasingly, public participation. I explore several examples, including an all-male production of Oscar Wilde's The Importance of Being Earnest (1895), which triggered a range of local and international responses, thereby exemplifying the complex historical, political and aesthetic dynamics of censorship in a highly globalized environment.
The Performance of Political Correctness
Authors: REINELT JANELLE
Published: May 2011

This article is about the power of cultural performances to shape and sometimes coerce public opinion and public behaviours. In the process, I intend to defend a concept which has few supporters these days: ‘political correctness’. So prevalent is this concept in our public discourse that its meanings have become habitual, thus ideologically invisible. Beginning with an examination of the term and its history, I situate it in relation to the arts through its relation to censorship, and frame it within the broad field of cultural performances to which it belongs. Concluding with a specific case study taken from theatre, I hope to perform a ‘correction’ of sorts – to reintroduce the term as a positive value and practice in an artistic milieu which has largely rejected its utility.
Naked Truth: Theatrical Performance and the Diagnostic Turn
Authors: FRIEZE JAMES
Published: May 2011

In a fashion that harks back to the birth of naturalistic drama, but also reflects contemporary anxieties about the etiolation of the real, the forensic capabilities of theatre have become, in the last two decades, the primary focus of theatrical attention. Reconsidering landmark works and rhetorical frames that helped to establish verbatim, virtual and in-yer-face theatre, this article explores the ways in which these key works and genres deploy, and attempt to jam, theatre's diagnostic machinery. The article contextualizes that machinery in relation to the medical underpinnings of naturalism, the growth of theatrical reflexivity from Pirandello to Beckett to Blast Theory, and the televisual phenomena of crime-scene investigation and fly-on-the-wall ‘reality shows’. In the final section I move to address two works which are explicitly about diagnosis, but which, in signal and purposeful ways, evade diagnosis: Must, by American performance artist Peggy Shaw and British company Clod Ensemble; and If That's All There Is, by UK-based company Inspector Sands.
Interdisciplinary progress in food production, food security and environment research
Authors: ACEVEDO MIGUEL F.
Published: May 2011

This review examines contributions of interdisciplinary (ID) research to understanding interactions between environmental quality, food production and food security. Global patterns of food insecurity and crop production are reviewed in relation to climate, land use and economic changes, as well as potential productivity increases compatible with environmental conservation. Interactions between food production and global processes make food insecurity a complex problem that requires ID analysis at local to global scales. Census and satellite data contribute to understanding of global cropland distribution. Analysis of land-use change exemplifies research between natural and social sciences. Quantitative modelling of global climate change impacts indicates relatively greater potential food insecurity in developing countries. International food security is increasingly interconnected through economic globalization and incentives for increased food production are required. Societies may not be able to expand available cropland without significant environmental risks; enhanced land and water productivity are the major opportunities available to increase food production. This requires renewed efforts in ID work to design and implement sound and efficient agricultural management practices. Models need to be informed by data from field experiments, long-term measurements and watershed monitoring by ground and remote sensing methods. Agricultural intensification may spare natural land but lead to increased pollution and water demand; reconciling conservation and productivity is a critical need. ID work provides many opportunities for synergies including conservation agriculture at the local level, efficient use of inputs, smarter land use taking into account spatial patterns and landscape ecology principles, and improved water management at field, system, watershed and basin levels. Goal-directed ID research is crucial, since producers, practitioners and policy makers should be involved. Geospatial, biotechnological and precision agriculture technologies linked with models can help inform strategies to achieve sustainable food production increases that maintain environmental quality. Implementation also requires ID work to overcome impediments due to human factors and facilitate adoption by farmers.
Interdisciplinary approaches for addressing marine contamination issues
Authors: FISHER NICHOLAS S. , CHEN CELIA Y.
Published: May 2011

Diverse chemical and biological processes in the oceans and atmosphere, the planet's most global domains, determine the fate and effects of marine contaminants and outbreaks of marine nuisance species. Understanding these problems requires the identification of environmental variables that influence ecological and human effects, the ability to predict spatial and temporal occurrences, and development of integrative interdisciplinary and mechanistic models for predicting their occurrences and severity. These endeavours require collaborative efforts of physical, chemical, biological and biomedical scientists working in interdisciplinary teams. There are numerous examples of interdisciplinary research conducted in marine systems on marine contaminants, including those contaminants released from the Earth's crust by human activities, those that are almost exclusively man-made in origin, and those that are biological contaminants often exacerbated by human activities. While interdisciplinary teams of researchers have greatly advanced the study of marine systems in some of these areas, there are still many barriers to interdisciplinary approaches in marine science, including disciplinary biases and institutional structures. A number of mechanisms are recommended that could support and enhance the ability of researchers to conduct interdisciplinary research in marine science, including the establishment of core facilities that can be used to support different teams of collaborating scientists, establishment of appropriate organizational structures, and promotion of seminars and symposia that emphasize interdisciplinary approaches.
Genetic characterization ofVibrio choleraeO1 strains isolated in Zambia during 1996–2004 possessing the unique VSP-II region of El Tor variant
Authors: BHUIYAN N. A. , NUSRIN S. , ANSARUZZAMAN M. , ISLAM A. , SULTANA M. , ALAM M. , ISLAM M. A. , CRAVIOTO A. , MUKHOPADHYAY A. K. , NAIR G. B. , MWASNA J. C. L. , ENDTZ H. P.
Published: May 2011

New variants ofVibrio choleraeO1 have appeared in different time-frames in various endemic regions, especially in Asia and Africa. Sixty-nine strains ofV. choleraeO1 isolated in Zambia between 1996 and 2004 were investigated by various genotypic techniques to determine the lineage of virulence signatures and clonality. All strains were positive forVibrioseventh pandemic Islands (VSP)-I and VSP-II and repeat toxin (RTX) gene clusters attesting their El Tor lineage. Interestingly, strains isolated in recent times (2003–2004) were identified as an altered variant (El Tor biotype that harbours El Tor typerstRbut produce classicalctxB) that replaced completely the progenitor El Tor strains prevalent in 1996–1997. Recent altered variant strains differed from prototype El Tor strains isolated earlier in that these strains lacked two ORFs, VC0493 and VC0498, in the VSP-II region. PFGE analysis revealed two major clonal lineages in the strains; cluster A represented the strains isolated before 2003 and cluster B the altered strains isolated in 2003–2004. Cluster A was closely related to prototype El Tor reference strain isolated in Bangladesh in 1971. Cluster B was found to be matched with Bangladeshi altered strains but was different from the hybrid strains isolated from Mozambique and Bangladesh. This report provides important information on the genesis of altered strains ofV. choleraeO1 isolated in Zambia and emphasizes the need for further studies to follow the trends of evolutionary changes.
Molecular and phylogenetic analysis of Greek measles 2010 strains
Authors: MELIDOU A. , GIOULA G. , POGKA V. , EXINDARI M. , MOUTOUSSI A. , SGOURAS D. , PAPADAKOS K. , CHATZIDIMITRIOU D. , KARABAXOGLOU D. , MENTIS A. , MALISIOVAS N.
Published: May 2011

Although elimination of measles virus (MV) by 2010 was a revised target, a new epidemic has been ongoing in Greece and other European countries. The purpose of this study was the molecular and phylogenetic analysis of the Greek MV circulating strain. Twenty-four MV strains isolated from clinical samples during the 2010 outbreak were genotyped and studied in terms of nucleotide variation and phylogeny. All of the detected viruses were of the D4 genotype, which is circulating in Greece in the Roma population of Bulgarian nationality, the Greek Roma population and the Greek non-minority population, as well as in other EU countries. Phylogenetic analysis revealed that these viruses belonged to subgroup 4 of D4 MV strains. It is essential to continue epidemiological surveillance of measles in Greece to monitor the transmission pattern of the virus and the effectiveness of measles immunization, which eventually will lead to its elimination.
Better Bounds for k-Partitions of Graphs
Authors: XU BAOGANG , YU XINGXING
Published: May 2011

Let G be a graph with m edges, and let k be a positive integer. We show that V(G) admits a k-partition V1, . . . Vk such that $e(V_i)\leq \frac 1{k^2}m+\frac {k-1}{2k^2}(\sqrt{2m+1/4}-1/2)$ for i ∈ {1, 2, . . . k}, and $e(V_1, \ldots, V_k)\geq \frac{k-1}{ k} m +\frac{k-1}{ 2k}\sqrt{2m+1/4} +O(k)$, where e(Vi) denotes the number of edges with both ends in Vi and $e(V_1,\ldots, V_k)=m-\sum_{i=1}^ke(V_i)$. This answers a problem of Bollobás and Scott [2] in the affirmative. Moreover, $\binom{k+1}{ 2}e(V_i)+\frac k2\sum_{j\ne i}e(V_j)\le m + O(k^2)$ for i ∈ {1, 2, . . ., k}, which is close to being best possible and settles another problem of Bollobás and Scott [2].
Shadow interest rates in Stockholm and the integration of early financial markets, 1660–1685: was Heckscher right?
Authors: Edvinsson Rodney
Published: May 2011

The decline of interest rates during the early modern period is considered an important factor in the subsequent rise of capitalist society. This article uses unique empirical material based on bills of exchange in Stockholm between 1660 and 1685 to estimate underlying ‘shadow interest rates’. It shows that annual rates ‘according’ to Stockholm were very high, mostly above 10 per cent, an indication of underdeveloped financial integration between Stockholm and the main European centres. There are also indications of a decline in these rates during the period studied, reflecting improved efficiency in Swedish financial markets.
ESCAPE DYNAMICS AND POLICY SPECIFICATION
Authors: Berardi Michele
Published: May 2011

In his monographThe Conquest of American Inflation(Princeton, NJ: Princeton University Press, 1999), Sargent suggests that the sharp reduction in U.S. inflation that took place under Volker may vindicate the type of econometric policy evaluation famously criticized by Lucas (Carnegie–Rochester Conference Series on Public Policy, 19–46, 1976). At the core of this vindication story is the escape dynamics, recurrent sliding away from the path leading to the time-consistent suboptimal equilibrium level of inflation and toward the low-inflation, optimal, time-inconsistent Ramsey outcome: by recurrently estimating a reduced-form model, in fact, the policy maker could periodically learn an approximate version of the natural rate hypothesis and therefore be induced to disinflate the economy. Two elements seem important in this story: the type of model used by the policy maker to represent the economy, whether structural or reduced-form, and the policy specification, whether derived taking the private sector's expectations as given or as endogenous to the policy design. Although Sargent (1999) stresses the first element, we find that it is instead the second aspect that is crucial to generate recurrent periods of low inflation: the policy maker has to recognize the endogeneity of the private sector's expectations and refrain from exploiting ephemeral short-run trade-offs between inflation and unemployment.
FAMILIES OF DIRAC OPERATORS AND QUANTUM AFFINE GROUPS
Authors: MICKELSSON JOUKO
Published: May 2011

TwistedK-theory classes over compact Lie groups can be realized as families of Fredholm operators using the representation theory of loop groups. In this paper we show how to deform the Fredholm family in the sense of quantum groups. The family of Dirac-type operators is parametrized by vectors in the adjoint module for a quantum affine algebra and transforms covariantly under a central extension of the algebra.
Minimizing the ruin probability through capital injections
Authors: Nie Ciyu , Dickson David C. M. , Li Shuanming
Published: May 2011

We consider an insurer who has a fixed amount of funds allocated as the initial surplus for a risk portfolio, so that the probability of ultimate ruin for this portfolio is at a known level. We consider the question of whether the insurer can reduce this ultimate ruin probability by allocating part of the initial funds to the purchase of a reinsurance contract. This reinsurance contract would restore the insurer's surplus to a positive level k every time the surplus fell between 0 and k. The insurer's objective is to choose the level k that minimizes the ultimate ruin probability. Using different examples of reinsurance premium calculation and claim size distribution we show that this objective can be achieved, often with a substantial reduction in the ultimate ruin probability from the situation when there is no reinsurance. We also show that by purchasing reinsurance the insurer can release funds for other purposes without altering its ultimate ruin probability.
The CBCL 1.5–5 and the identification of preschoolers with autism in Italy
Authors: Muratori F. , Narzisi A. , Tancredi R. , Cosenza A. , Calugi S. , Saviozzi I. , Santocchi E. , Calderoni S.
Published: May 2011

Aims.

To study the potential use of child behaviour checklist (CBCL) 1.5–5 scales for the early identification of preschoolers at risk of autism.

Methods.

CBCL scores of three groups of preschoolers were compared: (1) an experimental group of 101 preschoolers with autism spectrum disorder (ASD); (2) a control group of 95 preschoolers with other psychiatric disorders (OPD); (3) a control group of 117 preschoolers with typical development (TD). One-way analysis of variance (ANOVA), logistic regression with odds ratio (OR) and receiver operating characteristic (ROC) analyses were performed.

Results.

ANOVA revealed that ASD and OPD had significantly higher scores in almost all CBCL scales than TD. ASD presented significantly higher scores than OPD on Withdrawn, Attention Problems and Pervasive Developmental Problems (PDP) scales. Logistic regression analysis demonstrated that these same CBCL scales have validity in predicting the presence of an ASD towards both TD and OPD. ROC analysis indicated high sensitivity and specificity for PDP (0.85 and 0.90) and Withdrawn (0.89 and 0.92) scales when ASD is compared to TD. Specificity (0.60 for PDP and 0.65 for Withdrawn) decreases when comparing ASD and OPD

Conclusions.

The PDP and Withdrawn scales have a good predictive validity so that they could be proposed as a first-level tool to identify preschoolers at risk of autism in primary care settings. Problems regarding the lower specificity when comparing ASDv. OPD are discussed.
Pliocene Indonesian Throughflow and Leeuwin Current dynamics: Implications for Indian Ocean polar heat flux
Authors: Karas Cyrus , Nürnberg Dirk , Tiedemann Ralf , Garbe‐Schönberg Dieter
Published: May 2011

To understand the gradual global cooling during the mid‐Pliocene (3.5–2.5 Myr ago) one needs to consider the tectonical constriction of tropical seaways, which affected ocean circulation and the evolution of climate. Here we use paired measurements of δ18O and Mg/Ca ratios of planktonic foraminifera to reconstruct the Pliocene hydrography of the western tropical Indian Ocean (Site 709C) and changes in the Leeuwin Current in the eastern subtropical Indian Ocean (Site 763A) in response to Indonesian Gateway dynamics. Today, the Indonesian Throughflow (ITF) and, subsequently, the warm southward flowing Leeuwin Current off Western Australia are essential for the polar heat transport in the Indian Ocean. During 3.5–3 Ma, sea surface temperatures significantly dropped in the Leeuwin Current area, becoming since ∼3.3 Ma 2°C–3°C cooler than the rather unchanged sea surface temperatures from the eastern and western tropical Indian Ocean. We refer this drop in sea surface temperatures to a weakened Leeuwin Current with severe climatic effects on Western Australia induced by a tectonically reduced surface ITF. We suggest that this reduced surface ITF led to a diminished poleward heat transport in the Indian Ocean resulting in a weakened Leeuwin Current and possibly to cooling of the Benguela upwelling system.
On attraction of slime mould Physarum polycephalum to plants with sedative properties
Authors: Adamatzky Andrew
Published: May 2011

A plasmodium of acellular slime mould Physarum polycephalum is a large single cell with many nuclei. Presented to a configuration of attracting and repelling stimuli a plasmodium optimizes its growth pattern and spans the attractants, while avoiding repellents, with efficient network of protoplasmic tubes. Such behaviour is interpreted as computation and the plasmodium as an amorphous growing biological computer. Till recently laboratory prototypes of slime mould computing devices (Physarum machines) employed rolled oats and oat powder to represent input data. We explore alternative sources of chemo-attractants, which do not require a sophisticated laboratory synthesis. We show that plasmodium of P. polycephalum prefers sedative herbal tablets and dried plants to oat flakes and honey. In laboratory experiments we develop a hierarchy of slime-mould’s chemo-tactic preferences. We show that Valerian root (Valeriana officinalis) is the strongest chemo-attractant of P. polycephalum outperforming not only most common plants with sedative activities but also some herbal tablets.
A new functional role for lateral inhibition in the striatum: Pavlovian conditioning
Authors: Connor Patrick , Trappenberg Thomas
Published: May 2011

The striatum has long been implicated in reinforcement learning and has been suggested by several neurophysiological studies as the substrate for encoding the reward value of stimuli. Reward prediction error (RPE) has been used in several basal ganglia models as the underlying learning signal, which leads to Pavlovian conditioning abilities that can be simulated by the Rescorla-Wagner model.Lateral inhibition between striatal projection neurons was once thought to have a winner-take-all function, useful in selecting between possible actions. However, it has been noted that the necessary reciprocal connections for this interpretation are too few, and the relative strength of these synaptic connections is weak. Still, modeling studies show that lateral inhibition does have an overall suppression effect on striatal activity and may play an important role in striatal processing.Neurophysiological recordings show task-relevant ensembles of responsive neurons at specific points in a behavioral paradigm (Barnes et al., 2005), which appear to be induced by lateral inhibition (see Ponzi and Wickens, 2010). We have developed a similarly responding, RPE-based model of the striatum by incorporating lateral inhibition. Model neurons are assigned to either the direct or the indirect pathway but lateral connections occur within and between these groups, leading to competition between both the individual neurons and their pathways. We successfully applied this model to the simulation of Pavlovian phenomena beyond those of the Rescorla-Wagner model, including negative patterning, unovershadowing, and external inhibition.
Zero-mode anomalies of massless Dirac electron in graphene
Authors: Ando Tsuneya
Published: May 2011

A brief review is given on singularities appearing in electronic properties of monolayer graphene at the Dirac point from a theoretical point of view. The topics include effective-mass description of electronic states, singular behavior of the conductivity including the Hall effect and nonuniversality of the minimum conductivity, and the singular diamagnetic response to uniform and spatially varying magnetic field.
Nonresonant feeding of photonic crystal nanocavity modes by quantum dots
Authors: Laucht A. , Hauke N. , Neumann A. , Günthner T. , Hofbauer F. , Mohtashami A. , Müller K. , Böhm G. , Bichler M. , Amann M.-C. , Kaniber M. , Finley J. J.
Published: May 2011

We experimentally probe the nonresonant feeding of photons into the optical mode of a two dimensional photonic crystal nanocavity from the discrete emission from a quantum dot. For a strongly coupled system of a single exciton and the cavity mode, we track the detuning-dependent photoluminescence intensity of the exciton-polariton peaks at different lattice temperatures. At low temperatures we observe a clear asymmetry in the emission intensity depending on whether the exciton is at higher or lower energy than the cavity mode. At high temperatures this asymmetry vanishes when the probabilities to emit or absorb a phonon become similar. For a different dot-cavity system where the cavity mode is detuned by ΔE>5 meV to lower energy than the single exciton transitions emission from the mode remains correlated with the quantum dot as demonstrated unambiguously by cross-correlation photon counting experiments. By monitoring the temporal evolution of the photoluminescence spectrum, we show that feeding of photons into the mode occurs from multi-exciton transitions. We observe a clear anti-correlation of the mode and single exciton emission; the mode emission quenches as the population in the system reduces toward the single exciton level while the intensity of the mode emission tracks the multi-exciton transitions.
Loss mechanisms of quantum cascade lasers operating close to optical phonon frequencies
Authors: Castellano F. , Bismuto A. , Amanti M. I. , Terazzi R. , Beck M. , Blaser S. , Bächle A. , Faist J.
Published: May 2011

The extension of the operating frequency of Quantum Cascade Lasers (QCL) into the 20−50 μm regime is a desirable goal as it would bridge the gap between mid-infrared and THz devices. Coherent light emitters in this spectral range are also needed for spectroscopy and radio astronomy applications. Since little attention has been devoted to the subject in the past, we investigate the dominant loss mechanisms of QCLs in this spectral range. We report on an InGaAs/InAlAs QCL in an InP dielectric waveguide emitting at 23 μm wavelength whose electroluminescence spectrum shows an anomalous low-frequency cut which prevents laser action at low electric field. We also observe similar line shape in other GaAs/AlGaAs devices. The spectral features are analyzed and explained in terms of refractive index anomalies induced by phonon resonances.
The quantum spin Hall effect
Authors: Buhmann Hartmut
Published: May 2011

In a two-dimensional system the quantum spin Hall effect (QSHE) state is characterized by an insulating bulk and two counter-propagating helical edge states. These edge channels are protected by time reversal symmetry and spin currents propagate without dissipation. It was shown that HgTe-based quantum well structures are the most suitable candidates for its experimental realization. Here, the experimental requirements are discussed which lead to the observation of quantized edge channel transport which is one of the main signatures of the QSHE. Experiments will be presented which demonstrate the stability of the quantized conductance and its nonlocal character. Furthermore, evidence for the spin polarization of the QSHE edge channels is shown in an all-electrical measurement which demonstrates the potential of the QSHE for spin injection and detection applications in spintronics.
Optically-detected NMR of optically-hyperpolarized 31P neutral donors in 28Si
Authors: Steger M. , Sekiguchi T. , Yang A. , Saeedi K. , Hayden M. E. , Thewalt M. L. W. , Itoh K. M. , Riemann H. , Abrosimov N. V. , Becker P. , Pohl H.-J.
Published: May 2011

The electron and nuclear spins of the shallow donor 31P are promising qubit candidates invoked in many proposed Si-based quantum computing schemes. We have recently shown that the near-elimination of inhomogeneous broadening in highly isotopically enriched 28Si enables an optical readout of both the donor electron and nuclear spins by resolving the donor hyperfine splitting in the near-gap donor bound exciton transitions. We have also shown that pumping these same transitions can very quickly produce large electron and nuclear hyperpolarizations at low magnetic fields, where the equilibrium electron and nuclear polarizations are very small. Here we show preliminary results of the measurement of 31P neutral donor NMR parameters using this optical nuclear hyperpolarization mechanism for preparation of the 31P nuclear spin system, followed by optical readout of the resulting nuclear spin population after manipulation with NMR pulse sequences. This allows for the observation of single-shot NMR signals with very high signal-to-noise ratio under conditions where conventional NMR is not possible, due to the low concentration of 31P and the small equilibrium polarization.
An electron jet pump: The Venturi effect of a Fermi liquid
Authors: Taubert D. , Schinner G. J. , Tomaras C. , Tranitz H. P. , Wegscheider W. , Ludwig S.
Published: May 2011

A three-terminal device based upon a two-dimensional electron system is investigated in the regime of nonequilibrium transport. Excited electrons scatter with the cold Fermi sea and transfer energy and momentum to other electrons. A geometry analogous to a water jet pump is used to create a jet pump for electrons. Because of its phenomenological similarity we name the observed behavior the “electronic Venturi effect.”
Shape control of quantum dots studied by cross-sectional scanning tunneling microscopy
Authors: Keizer J. G. , Bozkurt M. , Bocquel J. , Mano T. , Noda T. , Sakoda K. , Clark E. C. , Bichler M. , Abstreiter G. , Finley J. J. , Lu W. , Rohel T. , Folliot H. , Bertru N. , Koenraad P. M.
Published: May 2011

In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.
Photon-to-electron quantum information transfer
Authors: Kosaka Hideo
Published: May 2011

Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
Effect of detuning on the phonon induced dephasing of optically driven InGaAs/GaAs quantum dots
Authors: Ramsay A. J. , Godden T. M. , Boyle S. J. , Gauger E. M. , Nazir A. , Lovett B. W. , Gopal Achanta Venu , Fox A. M. , Skolnick M. S.
Published: May 2011

Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses. The results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.
Magnetotransport in adsorbate-induced two-dimensional electron systems on cleaved InAs surfaces
Authors: Okamoto Tohru , Mochizuki Toshimitsu , Minowa Masaaki , Komatsuzaki Kazunari , Masutomi Ryuichi
Published: May 2011

This article reviews recent low-temperature magnetotransport measurements on two-dimensional electron systems (2DESs) formed at in situ cleaved InAs(110) surfaces by deposition of other materials. The surface donor level, at which the Fermi level of the 2DES is pinned, is determined from the saturation electron density for different kinds of adatoms. It decreases with increasing atomic ionization energy. For the case of Cs-deposition, the 2D electron density and mobility are studied over a wide coverage range. A clear increase in electron mobility appears above half monolayer coverage. For a surface covered with a submonolayer of Fe, hysteresis in the magnetoresistance is observed. It is associated with spin-glass ordering in the Fe film.
Defects in SiC for quantum computing
Authors: Weber J. R. , Koehl W. F. , Varley J. B. , Janotti A. , Buckley B. B. , Van de Walle C. G. , Awschalom D. D.
Published: May 2011

The successful implementation of the nitrogen-vacancy (NV) center in diamond as a qubit has spawned a great deal of interest in this defect. In principle, similar defects suitable for quantum computing should exist in other material systems; however, very little work has been done on identifying NV-like centers in other materials. We discuss the key properties of the NV center in diamond in the context of uncovering similar defects in other materials, with the specific example of SiC. Using first-principles calculations, we compare the properties of the NV center in diamond to the analogous defect in 4H-SiC. We also compare the properties of the bare vacancies. We calculate defect formation energies and charge-state transition levels to determine which defects are likely to form. Then, by analyzing the defect-induced electronic states, we determine whether stable defects in 4H-SiC may have properties similar to those of the NV center in diamond.
Switching ultrastrong light–matter coupling on a subcycle scale
Authors: Huber R. , Anappara A. A. , Günter G. , Sell A. , De Liberato S. , Ciuti C. , Biasiol G. , Sorba L. , Tredicucci A. , Leitenstorfer A.
Published: May 2011

Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron–photon interaction are discussed.
Intrinsic charge transport of conjugated organic molecules in electromigrated nanogap junctions
Authors: Song Hyunwook , Kim Youngsang , Jeong Heejun , Reed Mark A. , Lee Takhee
Published: May 2011

We present the measurement of charge transport through phenylene conjugated molecules using electromigrated nanogap junctions. To elucidate the intrinsic transport properties of the conjugated molecular junctions, a variety of molecular transport techniques were performed at low temperature, including inelastic electron tunneling spectroscopy, temperature- and length-variable transport measurements, and transition voltage spectroscopy. Such a self-consistent characterization of the molecular junction demonstrates the observation of intrinsic molecular properties in these junctions.
The invention and early history of the CCD
Authors: Smith George E.
Published: May 2011

As the first practical solid state imaging device, the invention of the charge coupled device has profoundly affected image sensing technology. They are used in a wide range of applications both as area and linear imaging devices starting with the replacement of imaging tubes used in commercial TV cameras and cam-corders. The rapid rise of their use in digital cameras has initiated the demise of film photography and created vast new markets with great economic benefit for many. Other uses include a wide variety of scientific, surveillance, and scanning applications. The inception of the device at Bell Labs by W. S. Boyle and G. E. Smith, Bell Syst. Tech. J. 49, 587 (1970);G. F. Amelio, M. F. Tompsett, and G. E. Smith, Bell Syst. Tech. J. 49, 593 (1970); W. S. Boyle and G. E. Smith, U.S. patent 3,792,322 (12 February 1974) was strongly influenced by several unique factors existing both within Bell Labs and the current world state of technology. These factors and their relevance will be discussed along with the train of thought leading to the invention. Early experimental devices and their initial applications were vigorously pursued and will be described. Mention of current applications will be given.
Single- and few-electron dynamic quantum dots in a perpendicular magnetic field
Authors: Wright S. J. , Thorn A. L. , Blumenthal M. D. , Giblin S. P. , Pepper M. , Janssen T. J. B. M. , Kataoka M. , Fletcher J. D. , Jones G. A. C. , Nicoll C. A. , Gumbs Godfrey , Ritchie D. A.
Published: May 2011

We present experimental studies of the current pumped through a dynamic quantum dot over a wide range of magnetic fields. At low fields we observe a repeatable structure indicating increased confinement of the electrons in the dynamic dot. At higher fields (B>5T), we observe a structure which changes markedly from device to device suggesting that in this regime the transport is sensitive to local disorder. The results are significant for the development of dynamic quantum dot pumps as quantum standards of electrical current.