Unified detection and tracking of instruments during retinal microsurgery

Methods for tracking an object have generally fallen into two groups: tracking by detection and tracking through local optimization. The advantage of detection-based tracking is its ability to deal with target appearance and disappearance, but it does not naturally take advantage of target motion continuity during detection. The advantage of local optimization is efficiency and accuracy, but it requires additional algorithms to initialize tracking when the target is lost. To bridge these two approaches, we propose a framework for unified detection and tracking as a time-series Bayesian estimation problem. The basis of our approach is to treat both detection and tracking as a sequential entropy minimization problem, where the goal is to determine the parameters describing a target in each frame. To do this we integrate the Active Testing (AT) paradigm with Bayesian filtering, and this results in a framework capable of both detecting and tracking robustly in situations where the target object enters and leaves the field of view regularly. We demonstrate our approach on a retinal tool tracking problem and show through extensive experiments that our method provides an efficient and robust tracking solution.

Biodiversity and Fishery Sustainability in the Lake Victoria Basin: An Unexpected Marriage?

Lake Victoria is Africa’s single most important source of inland fishery production. After it was initially fished down in the first half of the 20th century, Lake Victoria became home to a series of introduced food fishes, culminating in the eventual demographic dominance of the Nile perch, Lates niloticus. Simultaneously with the changes in fish stocks, Lake Victoria experienced dramatic changes in its ecology. The lake fishery during most of the 20th century was a multispecies fishery resting on a diverse lake ecosystem, in which native food fishes were targeted. The lake ended the century with a much more productive fishery, but one in which three species — two of them introduced — made up the majority of the catch. Although many fish stocks in Lake Victoria had declined before the expansion of the Nile perch population, a dramatic increase in the population size of Nile perch in the 1980s roughly coincided with the drastic decline or disappearance of many indigenous species. Now, two decades after the rise of Nile perch in Lake Victoria, this species has shown signs of being overfished, and some of the native species that were in retreat — or even thought extinct — are now reemerging. Data on the resurgence of the indigenous species suggest that heavy fishing of Nile perch may enhance biodiversity; this has spawned renewed interest in management options that promote both fishery sustainability and biodiversity conservation.

Effects of pH, light and temperature on (1→3,1→4)-β-glucanase stability in wheat leaves

Changes in (1→3,1→4)-β-D-glucan endohydrolase (EC 3.2.1.73) protein levels were investigated in segments from second leaves of wheat (Triticum aestivum L.). The abundance of the enzyme protein markedly increased when leaf segments were incubated in the dark whereas the enzyme rapidly disappeared when dark-incubated segments were illuminated or fed with sucrose. Addition of cycloheximide (CHI) to the incubation medium led to the disappearance of previously synthesized (1→3,1→4)-β-glucanase and suppressed the dark-induced accumulation indicating that the enzyme was rather unstable. The degradation of (1→3,1→4)-β-glucanase was analyzed without the interference of de-novo synthesis in intercellular washing fluid (IWF). The loss of the enzyme protein during incubation of IWF (containing naturally present peptide hydrolases) indicated that the stability increased from pH 4 to pH 7 and that an increase in the temperature from 25 to 35 °C considerably decreased the stability. Chelating divalent cations in the IWF with o-phenanthroline also resulted in a lowered stability of the enzyme. A strong temperature effect in the range from 25 to 35 °C was also observed in wheat leaf segments. Diurnal changes in (1→3,1→4)-β-glucanase activity were followed in intact second leaves from young wheat plants. At the end of the dark period, the activity was high but constantly decreased during the light phase and remained low if the light period was extended. Activity returned to the initial level during a 10-h dark phase. During a diurnal cycle, changes in (1→3,1→4)-β-glucanase activity were associated with reciprocal changes in soluble carbohydrates. The results suggest that the synthesis and the proteolytic degradation of an apoplastic enzyme may rapidly respond to changing environmental conditions.

The sonic hedgehog signaling pathway and the development of pharyngeal arch Derivatives in Haplochromis piceatus, a Lake Victoria cichlid

Objectives Pharyngeal arches develop in the head and neck regions, and give rise to teeth, oral jaws, the hyoid bone, operculum, gills, and pharyngeal jaws in teleosts. In this study, the expression patterns of genes in the sonic hedgehog (shh), wnt, ectodysplasin A (eda), and bone morphogenetic protein (bmp) pathways were investigated in the pharyngeal arches of Haplochromis piceatus, one of the Lake Victoria cichlids. Furthermore, the role of the shh pathway in pharyngeal arch development in H. piceatus larvae was investigated. Methods The expression patterns of lymphocyte enhancer binding factor 1 (lef1), ectodysplasin A receptor (edar), shh, patched 1 (ptch1), bmp4, sp5 transcription factor (sp5), sclerostin domain containing 1a (sostdc1a), and dickkopf 1 (dkk1) were investigated in H. piceatus larvae by in situ hybridization. The role of the shh pathway was investigated through morphological phenotypic characterization after its inhibition. Results We found that lef1, edar, shh, ptch1, bmp4, dkk1, sostdc1a, and sp5 were expressed not only in the teeth, but also in the operculum and gill filaments of H piceatus larvae. After blocking the shh pathway using cyclopamine, we observed ectopic shh expression and the disappearance of ptch1 expression. After six weeks of cyclopamine treatment, an absence of teeth in the oral upper jaws and a poor outgrowth of premaxilla, operculum, and gill filaments in juvenile H. piceatus were observed. Conclusions These results suggest that the shh pathway is important for the development of pharyngeal arch derivatives such as teeth, premaxilla, operculum, and gill filaments in H. piceatus.

A physiological and behavioral mechanism for leaf-herbivore induced systemic root resistance

Indirect plant-mediated interactions between herbivores are important drivers of community composition in terrestrial ecosystems. Among the most striking examples are the strong indirect interactions between spatially separated leaf- and root-feeding insects sharing a host plant. Although leaf feeders generally reduce the performance of root herbivores, little is known about the underlying systemic changes in root physiology and the associated behavioral responses of the root feeders. We investigated the consequences of maize (Zea mays) leaf infestation by Spodoptera littoralis caterpillars for the root-feeding larvae of the beetle Diabrotica virgifera virgifera, a major pest of maize. D. virgifera strongly avoided leaf-infested plants by recognizing systemic changes in soluble root components. The avoidance response occurred within 12 h and was induced by real and mimicked herbivory, but not wounding alone. Roots of leaf-infested plants showed altered patterns in soluble free and soluble conjugated phenolic acids. Biochemical inhibition and genetic manipulation of phenolic acid biosynthesis led to a complete disappearance of the avoidance response of D. virgifera. Furthermore, bioactivity-guided fractionation revealed a direct link between the avoidance response of D. virgifera and changes in soluble conjugated phenolic acids in the roots of leaf-attacked plants. Our study provides a physiological mechanism for a behavioral pattern that explains the negative effect of leaf attack on a root-feeding insect. Furthermore, it opens up the possibility to control D. virgifera in the field by genetically mimicking leaf herbivore-induced changes in root phenylpropanoid patterns.

Long-term forest fire ecology and dynamics in southern Switzerland

1 Pollen and charcoal analysis at two lakes in southern Switzerland revealed that fire has had a prominent role in changing the woodland composition of this area for more than 7000 years. 2 The sediment of Lago di Origlio for the period between 5100 and 3100 bc cal. was sampled continuously with a time interval of about 10 years. Peaks of charcoal particles were significantly correlated with repeated declines in pollen of Abies, Hedera, Tilia, Ulmus, Fraxinus excelsior t., Fagus and Vitis and with increases in Alnus glutinosa t., shrubs (e.g. Corylus, Salix and Sambucus nigra t.) and several herbaceous species. The final disappearance of the lowland Abies alba stands at around 3150 bc cal. may be an example of a fire-caused local extinction of a fire-intolerant species. 3 Forest fires tended to diminish pollen diversity. The charcoal peaks were preceded by pollen types indicating human activity. Charcoal minima occurred during periods of cold humid climate, when fire susceptibility would be reduced. 4 An increase of forest fires at about 2100 bc cal. severely reduced the remaining fire-sensitive plants: the mixed-oak forest was replaced by a fire-tolerant alder–oak forest. The very strong increase of charcoal influx, and the marked presence of anthropogenic indicators, point to principally anthropogenic causes. 5 We suggest that without anthropogenic disturbances Abies alba would still form lowland forests together with various deciduous broadleaved tree taxa.

Constitutive IL-2 mRNA expression in lymphocytes, infected with the intracellular parasite Theileria parva.

Theileria parva-infected lymphoblastoid cell lines of T or B cell origin were examined for IL-2 mRNA expression. T. parva-infected T cell lines could be of the CD4-CD8-, CD4+CD8-, CD4-CD8+, or CD4+CD8+ phenotype and express alpha beta or gamma delta TCR. By Northern blot analysis and amplification by the polymerase chain reaction, IL-2 mRNA could be detected in all T. parva-infected cell lines tested. IL-2 mRNA expression was also shown to be dependent on the continuous presence of the parasite in the host cell cytoplasm, because elimination of the parasite by treatment of T. parva-infected cell cultures with the theilericidal drug BW720c resulted in the disappearance of detectable IL-2 mRNA. The effect of anti-IL-2 antibodies on the proliferation of T. parva-infected cells was also tested. Inhibition experiments suggest that although IL-2 mRNA can be detected in all cell lines tested, not all T. parva-infected cell lines are dependent on IL-2 for their proliferation. Our data provide the first example for the constitutive expression of IL-2 mRNA in T and B cells caused by infection with an intracellular parasite.

Tissue Crowding Induces Caspase-Dependent Competition for Space.

Regulation of tissue size requires fine tuning at the single-cell level of proliferation rate, cell volume, and cell death. Whereas the adjustment of proliferation and growth has been widely studied [1, 2, 3, 4 and 5], the contribution of cell death and its adjustment to tissue-scale parameters have been so far much less explored. Recently, it was shown that epithelial cells could be eliminated by live-cell delamination in response to an increase of cell density [6]. Cell delamination was supposed to occur independently of caspase activation and was suggested to be based on a gradual and spontaneous disappearance of junctions in the delaminating cells [6]. Studying the elimination of cells in the midline region of the Drosophila pupal notum, we found that, contrary to what was suggested before, Caspase 3 activation precedes and is required for cell delamination. Yet, using particle image velocimetry, genetics, and laser-induced perturbations, we confirmed [ 6] that local tissue crowding is necessary and sufficient to drive cell elimination and that cell elimination is independent of known fitness-dependent competition pathways [ 7, 8 and 9]. Accordingly, activation of the oncogene Ras in clones was sufficient to compress the neighboring tissue and eliminate cells up to several cell diameters away from the clones. Mechanical stress has been previously proposed to contribute to cell competition [ 10 and 11]. These results provide the first experimental evidences that crowding-induced death could be an alternative mode of super-competition, namely mechanical super-competition, independent of known fitness markers [ 7, 8 and 9], that could promote tumor growth.

Physics potential of a long-baseline neutrino oscillation experiment using a J-PARC neutrino beam and Hyper-Kamiokande

Hyper-Kamiokande will be a next generation underground water Cherenkov detector with a total (fiducial) mass of 0.99 (0.56) million metric tons, approximately 20 (25) times larger than that of Super-Kamiokande. One of the main goals of HyperKamiokande is the study of CP asymmetry in the lepton sector using accelerator neutrino and anti-neutrino beams. In this paper, the physics potential of a long baseline neutrino experiment using the Hyper-Kamiokande detector and a neutrino beam from the J-PARC proton synchrotron is presented. The analysis uses the framework and systematic uncertainties derived from the ongoing T2K experiment. With a total exposure of 7.5 MW × 10⁷ s integrated proton beam power (corresponding to 1.56 × 10²² protons on target with a 30 GeV proton beam) to a 2.5-degree off-axis neutrino beam, it is expected that the leptonic CP phase δCP can be determined to better than 19 degrees for all possible values of δCP , and CP violation can be established with a statistical significance of more than 3 σ (5 σ) for 76% (58%) of the δCP parameter space. Using both νe appearance and νµ disappearance data, the expected 1σ uncertainty of sin²θ₂₃ is 0.015(0.006) for sin²θ₂₃ = 0.5(0.45).

Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam

T2K reports its first measurements of the parameters governing the disappearance of νµ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic νµ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector SuperKamiokande, 295 km away, where the νµ survival probability is expected to be minimal. Using a dataset corresponding to 4.01×10²⁰ protons on target, 34 fully contained µ-like events were observed. The best-fit oscillation parameters are sin²(θ₂₃) = 0.45 and |∆m^2_32| = 2.51 × 10⁻³ eV² with 68% confidence intervals of 0.38 - 0.64 and 2.26 - 2.80 ×10⁻³ eV² respectively. These results are in agreement with existing antineutrino parameter measurements and also with the νµ disappearance parameters measured by T2K.

Long-term Responses of Mountain Ecosystems to Environmental Changes: Resilience, Adjustment, and Vulnerability

The steep environmental gradients of mountain ecosystems over short distances reflect large gradients of several climatic parameters and hence provide excellent possibilities for ecological research on the effects of environmental change. To gain a better understanding of the dynamics of abiotic and biotic parameters of mountain ecosystems, long-term records are required since permanent plots in mountain regions cover in the best case about 50 - 70 years. In order to extend investigations of ecological dynamics beyond these temporal limitations of permanent plots, paleoecological approaches can be used if the sampling resolution can be adapted to ecological research questions, e.g. a sample every 10 years. Paleoecological studies in mountain ecosystems can provide new ecological insights through the combination of different spatial and temporal scales. [f we thus improve our understanding of processes across both steep environmental gradients and different time scales, we may be able to better estimate ecosystem responses to current and future environmental change (Ammann et al. 1993; Lotter et al. 1997). The complexity of ecological interactions in mountain regions forces us to concentrate on a number of sub-systems - without losing sight of the wider context. Here, we summarize a few case studies on the effects of Holocene climate change and disturbance on the vegetation of the Western Alps. To categorize the main response modes of vegetation to climatic change and disturbance in the Alps we use three classes of ecological behaviour: "resilience", "adjustment", and "vulnerability", We assume a resilient (or elastic) behaviour if vegetation is able to recover to its former state, regaining important ecosystem characteristics, such as floristic composition, biodiversity, species abundances, and biomass (e.g. Küttel 1990; Aber and Melillo 199 1). Conversely, vegetation displacements may occur in response to climatic change and/or disturbance. In some cases, this may culminate in irreversible large-scale processes such as species and/or community extinctions. Such drastic developments indicate high ecosystem vulnerability (or inelasticity or instability, for detailed definitions see Küttel 1990; Aber and Melillo 199 1) to climatic change and/or disturbance. In this sense, the "vulnerability" (or instability) of an ecosystem is expressed by the degree of failure to recover to the original state before disturbance and/or climatic change. Between these two extremes (resilience vs. vulnerability), ecosystem adjustments to climatic change and/or disturbance may occur, including the appearance of new and/or the disappearance of old species. The term "adjustment" is hence used to indicate the response of vegetational communities, which adapted to new environmental conditions without losing their main character. For forest ecosystems, we assume vegetational adjustments (rather than vulnerability) if the dominant (or co-dominant) tree species are not outnumbered or replaced by formerly unimportant plant species or new invaders. Adaptation as a genetic process is not discussed here and will require additional pbylogeographical studies (that incorporate the analysis of ancient DNA) in order to fully understand the distributions of ecotypes.

Ausmass und Auswirkungen der Waldbrände auf die Vegetation der Schweiz im Laufe der Jahrtausende

New palaeoecological investigations (pollen, macrofossil, and charcoal analyses) provide important evidence on the fire history and the long-term fire ecology of different regions of Switzerland. The results from the Swiss plateau, the Northern and Central Alps and Southern Switzerland suggest that fire played a different role for the long-term vegetational development in the different regions. In the Northern Alps and Southern Switzerland anthropogenic fires led to the disappearance of entire forest communities. These fires especially affected the fire-sensitive species Abies alba. On the Swiss Plateau fire frequencies were markedly lower than in the Southern Alps. Nevertheless, fires probably led to a decline in the occurrence of fire-sensitive taxa such as Ulmus, Fraxinus excelsior or Tilia at lower altitudes (Fagus silvatica-Quercus belt). First evidences from the Central Alps suggest that forest fires were naturally more frequent in this continental region and that the vegetation might be better fire-adapted than the original (partly or completely vanished) plant communities of the Swiss Plateau, the Northern Alps and Southern Switzerland.