Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples

A creative low-cost and compact mechanical device that mimics the rapid closure of the pistol shrimp claw was used to conduct electrochemical experiments, in order to study the effects of hydrodynamic cavitation on the corrosion of aluminum and steel samples. Current-time curves show significant changes associated with local variations in dissolved O2 concentration, cavitation-induced erosion and changes in the nature of the surface corrosion products

Sedimentary Facies of the Eastern Pacific\u27s Northernmost Reef-Like Setting (Cabo Pulmo, Mexico)

Cabo Pulmo, Mexico, is often cited as the eastern Pacific\u27s northernmost coral reef. We investigated sedimentary dynamics to verify whether the system functions sedimentologically as a reef, which would mean that it retained internal sediment in a framework and exported peri-reefal sediment creating clearly identifiable facies dominated by reefal fauna. We mapped distribution of sediments using grab samples, the acoustic ground-discrimination systems QTC View and Echoplus at 50 kHz signal frequency and an IKONOS satellite image. Morphologically, the bay of Cabo Pulmo can be divided into intrusive dikes and rocky hardgrounds in less than 10 m depth and a sandy interior with rocky outcrops sloping to over 40 m. Reefal fauna without lasting framework-building but with production of typically reef-associated carbonate sediments, as well as a patch-reef facies were found on the dikes and hardgrounds. Sediments in the bay were a mixture of carbonates and siliciclastics and were influenced by a seasonal river near the bay\u27s center that imported siliciclastic material. To the north and south sediments had a higher carbonate content, although overall the bay was characterized by \u3e 50% siliciclastics. The shallower subtidal sands were dominated by mollusk fragments, whereas in depths \u3e 30 m planktonic foraminiferal sand was found. Acoustically and optically remote-sensed maps were used to differentiate between the rocky and sandy areas and to identify the presumed off-shelf transport pathway of reef-derived carbonates. Overall, the sedimentary system is characterized by carbonate production, but the coarser reef derived carbonates (coral and reef-dwelling mollusks) are transported off-shelf along a steep depth gradient and little typical peri-reef sediment remains. This transport is likely aided by storms. Since no sediment retaining frameworks are formed, the dikes cannot retain internal sediment, and the reefal fauna was not dominant in sediments throughout the bay, we conclude that Cabo Pulmo sedimentologically functions only in a limited way like a coral reef

Probabilistic Tracking and Behavior Identification of Fluorescent Particles

Explicit and tractable characterizations of the dynamical behavior of virus particles are pivotal for a thorough understanding of the infection mechanisms of viruses. This thesis deals with the problem of extracting symbolic representations of the dynamical behavior of fluorescent particles from fluorescence microscopy image sequences. The focus is on the behavior of virus particles such as fusion with the cell membrane. A numerical representation is obtained by tracking the particles in the image sequences. We have investigated probabilistic tracking approaches, including approaches based on the Kalman filter as well as based on particle filters. For reasons of efficiency and robustness, we developed a tracking approach based on the probabilistic data association (PDA) algorithm in combination with an ellipsoidal sampling scheme that exploits effectively the image data via parametric appearance models. To track objects in close proximity, we compute the support that each image position provides to each tracked object relative to the support provided to the object's neighbors. After tracking, the problem of mapping the trajectory information computed by the tracking approaches to symbolic representations of the behavior arises. To compute symbolic representations of behaviors related to the fusion of single virus particles with the cell membrane based on their intensity over time, we developed a layered probabilistic approach based on stochastic hybrid systems as well as hidden Markov models (HMMs). We use a maxbelief strategy to efficiently combine both representations. The layered approach describes the intensity, intensity models, and behaviors of single virus particles. We introduce models for the evolution of the intensity and the behavior. To compute estimates for the intensity, intensity models, and behaviors we use a hybrid particle filter and the Viterbi algorithm. The developed approaches have been applied to synthetic images as well as to real microscopy image sequences displaying human immunodeficiency virus (HIV-1) particles. We have performed an extensive quantitative evaluation of the performance and a comparison with several existing approaches. It turned out that our approaches outperform previous ones, thus yielding more accurate and more reliable information about the behavior of virus particles. Moreover, we have successfully applied our tracking approaches to 3D image sequences displaying herpes simplex virus (HSV) replication compartments. We also applied the tracking approaches to image data displaying microtubule tips and analyzed their motion. In addition, our tracking approaches were successfully applied to the 2D and 3D image data of a Particle Tracking Challenge

Hormonal regulation of alveolarization: structure-function correlation

BACKGROUND: Dexamethasone (Dex) limits and all-trans-retinoic acid (RA) promotes alveolarization. While structural changes resulting from such hormonal exposures are known, their functional consequences are unclear. METHODS: Neonatal rats were treated with Dex and/or RA during the first two weeks of life or were given RA after previous exposure to Dex. Morphology was assessed by light microscopy and radial alveolar counts. Function was evaluated by plethysmography at d13, pressure volume curves at d30, and exercise swim testing and arterial blood gases at both d15 and d30. RESULTS: Dex-treated animals had simplified lung architecture without secondary septation. Animals given RA alone had smaller, more numerous alveoli. Concomitant treatment with Dex + RA prevented the Dex-induced changes in septation. While the results of exposure to Dex + RA were sustained, the effects of RA alone were reversed two weeks after treatment was stopped. At d13, Dex-treated animals had increased lung volume, respiratory rate, tidal volume, and minute ventilation. On d15, both RA- and Dex-treated animals had hypercarbia and low arterial pH. By d30, the RA-treated animals resolved this respiratory acidosis, but Dex-treated animals continued to demonstrate blood gas and lung volume abnormalities. Concomitant RA treatment improved respiratory acidosis, but failed to normalize Dex-induced changes in pulmonary function and lung volumes. No differences in exercise tolerance were noted at either d15 or d30. RA treatment after the period of alveolarization also corrected the effects of earlier Dex exposure, but the structural changes due to RA alone were again lost two weeks after treatment. CONCLUSION: We conclude that both RA- and corticosteroid-treatments are associated with respiratory acidosis at d15. While RA alone-induced changes in structure andrespiratory function are reversed, Dex-treated animals continue to demonstrate increased respiratory rate, minute ventilation, tidal and total lung volumes at d30. Concomitant treatment with Dex + RA prevents decreased septation induced by Dex alone and results in correction of hypercarbia. However, these animals continue to have abnormal pulmonary function and lung volumes. Increased septation as a result of RA treatment alone is reversed upon discontinuation of treatment. These data suggest that Dex + RA treatment results in improved gas exchange likely secondary to normalized septation

A rapid change in virulence gene expression during the transition from the intestinal lumen into tissue promotes systemic dissemination of Salmonella.

Bacterial pathogens causing systemic disease commonly evolve from organisms associated with localized infections but differ from their close relatives in their ability to overcome mucosal barriers by mechanisms that remain incompletely understood. Here we investigated whether acquisition of a regulatory gene, tviA, contributed to the ability of Salmonella enterica serotype Typhi to disseminate from the intestine to systemic sites of infection during typhoid fever. To study the consequences of acquiring a new regulator by horizontal gene transfer, tviA was introduced into the chromosome of S. enterica serotype Typhimurium, a closely related pathogen causing a localized gastrointestinal infection in immunocompetent individuals. TviA repressed expression of flagellin, a pathogen associated molecular pattern (PAMP), when bacteria were grown at osmotic conditions encountered in tissue, but not at higher osmolarity present in the intestinal lumen. TviA-mediated flagellin repression enabled bacteria to evade sentinel functions of human model epithelia and resulted in increased bacterial dissemination to the spleen in a chicken model. Collectively, our data point to PAMP repression as a novel pathogenic mechanism to overcome the mucosal barrier through innate immune evasion

Living on the Edge: High-Latitude Porites Carbonate Production Under Temperate Eutrophic Conditions

Non-framework building high-latitude coral communities have recently received increased attention as a result of their potential to act as refugia during global change, as proxies for such change and for testing the environmental tolerance limits of various species of coral. In this study, we report on high-resolution in situ measured environmental factors influencing the development of monospecific (Porites panamensis) non-framework building coral communities and the resulting coral-derived carbonate sediment production in the northern Gulf of California, Mexico (Bahía de Los Angeles, 29°N, 113°E). Half-hourly measurements of temperature and chlorophyll a (a nutrient proxy) for a 1-year period indicate temperature extremes ranging from 14°C to 30°C, and average chlorophyll a values of 2.2 mg Chl a/m3(eutrophic). Even though P. panamensis only occur as small massive and encrusting colonies, they nonetheless show a significant carbonate sediment production potential (0.14 kg CaCO3/m2/year). A calculation of carbonate production rates vs amount of coral found in the sediment shows that this high-latitude community must have persisted for an extended period of time

Experimental and computational analyses reveal that environmental restrictions shape HIV-1 spread in 3D cultures

Here, using an integrative experimental and computational approach, Imle et al. show how cell motility and density affect HIV cell-associated transmission in a three-dimensional tissue-like culture system of CD4+ T cells and collagen, and how different collagen matrices restrict infection by cell-free virions