450 research outputs found
Visual perception of digital holograms on autostereoscopic displays
In digital holography we often capture optically a 3D scene and reconstruct the perspectives numerically. The
reconstructions are routinely in the form of a 2D image slice, an extended focus image, or a depth map from
a single perspective. These are fundamentally 2D (or at most 2.5D) representations and for some scenes are
not certain to give the human viewer a clear perception of the 3D features encoded in the hologram (occlusions
are not overcome, for example). As an intermediate measure towards a full-field optoelectronic display device,
we propose to digitally process the holograms to allow them to be displayed on conventional autostereoscopic
displays
Comparing numerical error and visual quality in reconstructions from compressed digital holograms
Digital holography is a well-known technique for both sensing and displaying real-world three-dimensional objects.
Compression of digital holograms has been studied extensively, and the errors introduced by lossy compression are routinely evaluated in a reconstruction domain. Mean-square error predominates in the evaluation of reconstruction quality. However, it is not known how well this metric corresponds to what a viewer would regard as perceived error, nor how consistently it functions across different holograms and different viewers. In this study, we evaluate how each of seventeen viewers compared the visual quality of compressed and uncompressed holograms' reconstructions. Holograms from five different three-dimensional objects were used in the study, captured using a phase-shift digital holography setup. We applied two different lossy compression techniques to the complex-valued hologram pixels: uniform quantization, and removal and quantization of the Fourier coefficients, and used seven different compression levels with each
Competitive assembly of South Pacific invasive ant communities
<p>Abstract</p> <p>Background</p> <p>The relative importance of chance and determinism in structuring ecological communities has been debated for nearly a century. Evidence for determinism or assembly rules is often evaluated with null models that randomize the occurrence of species in particular locales. However, analyses of the presence or absence of species ignores the potential influence of species abundances, which have long been considered of major importance on community structure. Here, we test for community assembly rules in ant communities on small islands of the Tokelau archipelago using both presence-absence and abundance data. We conducted three sets of analyses on two spatial scales using three years of sampling data from 39 plots on 11 islands.</p> <p>Results</p> <p>First, traditional null model tests showed support for negative species co-occurrence patterns among plots within islands, but not among islands. A plausible explanation for this result is that analyses at larger spatial scales merge heterogeneous habitats that have considerable effects on species occurrences. Second, analyses of ant abundances showed that samples with high ant abundances had fewer species than expected by chance, both within and among islands. One ant species, the invasive yellow crazy ant <it>Anoplolepis gracilipes</it>, appeared to have a particularly strong effect on community structure correlated with its abundance. Third, abundances of most ant species were inversely correlated with the abundances of all other ants at both spatial scales. This result is consistent with competition theory, which predicts species distributions are affected by diffuse competition with suites of co-occurring species.</p> <p>Conclusion</p> <p>Our results support a pluralistic explanation for ant species abundances and assembly. Both stochastic and deterministic processes interact to determine ant community assembly, though abundance patterns clearly drive the deterministic patterns in this community. These deterministic patterns were observed at two spatial scales. Results indicate that abundance-based null models may be more sensitive in detecting non-random patterns in community assembly than species co-occurrences analyses.</p
Communities in university mathematics
This paper concerns communities of learners and teachers that are formed, develop and interact in university mathematics environments through the theoretical lens of Communities of Practice. From this perspective, learning is described as a process of participation and reification in a community in which individuals belong and form their identity through engagement, imagination and alignment. In addition, when inquiry is considered as a fundamental mode of participation, through critical alignment, the community becomes a Community of Inquiry. We discuss these theoretical underpinnings with examples of their application in research in university mathematics education and, in more detail, in two Research Cases which focus on mathematics students' and teachers' perspectives on proof and on engineering students' conceptual understanding of mathematics. The paper concludes with a critical reflection on the theorising of the role of communities in university level teaching and learning and a consideration of ways forward for future research
18F-fluoride PET: changes in uptake as a method to assess response in bone metastases from castrate-resistant prostate cancer patients treated with 223Ra-chloride (Alpharadin)
Am I in the right place? : Academic engagement and study success during the first years at university
Entrance to university does not automatically lead to high academic engagement and success, and there may be individual differences in student engagement. In the present study, university students' (N = 668) academic engagement and disengagement profiles, and the differences between them in terms of academic achievement, were investigated. Students from introductory courses were classified by Latent Profile Analysis (LPA) into homogenous groups having similar patterns according to the following variables: study engagement, study-related exhaustion, lack of interest, lack of self-regulation, and uncertainty of one's career choice. Four groups of students were identified: engaged, disengaged, undecided, and alienated. Engaged students received the highest grades, with disengaged and undecided students performing most poorly. In addition, the profiles were related to the behavioral indicators of engagement (i.e., ECTS credits). Even after two years of studying, engaged students were performing better than disengaged students. The study's implications for both research and practice are discussed. (C) 2016 Elsevier Inc. All rights reserved.Peer reviewe
ROS-mediated TNF-α and MIP-2 gene expression in alveolar macrophages exposed to pine dust
BACKGROUND: Respiratory symptoms, impaired lung function, and asthma have been reported in workers exposed to wood dust in a number of epidemiological studies. The underlying pathomechanisms, however, are not well understood. Here, we studied the effects of dust from pine (PD) and heat-treated pine (HPD) on the release of reactive oxygen species (ROS) and inflammatory mediators in rat alveolar macrophages. METHODS: Tumour necrosis factor-alpha (TNF-α) and macrophage inflammatory protein-2 (MIP-2) protein release, TNF-α and MIP-2 mRNA expression, and generation of ROS were studied as end points after treatment of rat alveolar macrophages with PD or HPD. In a separate series of experiments, the antioxidants glutathione and N-acetyl-L-cysteine were included in combination with wood dust. To determine the endogenous oxidative and antioxidant capacity of wood dusts, electron spin resonance (ESR) spectroscopy was used. RESULTS: After 4 h incubation, both PD and HPD elicited a significantly (p < 0.05) increased mRNA expression of TNF-α and MIP-2 as well as a concentration-dependent release of TNF-α and MIP-2 protein. Interestingly, PD induced a significantly higher TNF-α and MIP-2 production than HPD. Moreover, a significantly increased ROS production was observed in alveolar macrophages exposed to both PD and HPD. In the presence of the antioxidants glutathione and N-acetyl-L-cysteine, the PD- and HPD-induced release of ROS, TNF-α, and MIP-2 was significantly reduced. Finally, electron spin resonance analyses demonstrated a higher endogenous antioxidant capacity of HPD compared to PD. Endotoxin was not present in either dust sample. CONCLUSION: These results indicate that pine dust is able to induce expression of TNF-α and MIP-2 in rat alveolar macrophages by a mechanism that is, at least in part, mediated by ROS
The autoinducer synthases LuxI and AinS are responsible for temperature-dependent AHL production in the fish pathogen Aliivibrio salmonicida
Published version, also available at http://dx.doi.org/10.1186/s12866-015-0402-zBackground: Quorum sensing (QS) is a cell-to-cell communication system used by bacteria to regulate activities
such as virulence, bioluminescence and biofilm formation. The most common QS signals in Gram-negative bacteria
are N-acyl-homoserine lactones (AHLs). Aliivibrio salmonicida is the etiological agent of cold water vibriosis in
Atlantic salmon, a disease which occurs mainly during seasons when the seawater is below 12°C. In this work we
have constructed several mutants of A. salmonicida LFI1238 in order to study the LuxI/LuxR and AinS/AinR QS
systems with respect to AHL production and biofilm formation.
Results: Using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) we found that
LuxI in A. salmonicida LFI1238 is responsible for producing seven of the different AHLs, whereas AinS is responsible
for producing only one. The production of these various AHLs is dependent on both cell density and growth
temperature. The AHLs were efficiently produced when wild type LFI1238 was grown at 6 or 12°C, however at
16°C AHL production decreased dramatically, and LFI1238 produced less than 5% of the maximum concentrations
observed at 6°C. LitR, the master regulator of QS, was found to be a positive regulator of AinS-dependent AHL
production, and to a lesser extent LuxI-dependent AHL production. This implies a connection between the two
systems, and both systems were found to be involved in regulation of biofilm formation. Finally, inactivation of
either luxR1 or luxR2 in the lux operon significantly reduced production of LuxI-produced AHLs.
Conclusion: LuxI and AinS are the autoinducer synthases responsible for the eight AHLs in A. salmonicida. AHL
production is highly dependent on growth temperature, and a significant decrease was observed when the
bacterium was grown at a temperature above its limit for disease outbreak. Numerous AHLs could offer the
opportunity for fine-tuning responses to changes in the environment
Recombinant human activated protein C attenuates endotoxin-induced lung injury in awake sheep
Introduction: Acute lung injury often complicates severe sepsis.
In Gram-negative sepsis, bacterial endotoxin activates both
coagulation and inflammation. Enhanced lung vascular
pressures and permeability, increased extravascular lung water
content and deteriorated gas exchange characterize ovine
endotoxin-induced lung injury, a frequently used model of acute
lung injury. Recombinant human activated protein C (rhAPC),
with its anticoagulant, anti-inflammatory, fibrinolytic and
antiapoptotic effects, reportedly reduces the respiratordependent
days and the mortality of patients with severe sepsis.
We speculate whether rhAPC antagonizes endotoxin-induced
lung injury in sheep.
Methods: Two groups of sheep were exposed to Escherichia
coli endotoxin (lipopolysaccharide) 15 ng/kg/minute
intravenously from 0 to 24 hours; one group received only
lipopolysaccharide throughout (n = 8), and the other group
received lipopolysaccharide in combination with rhAPC 24 ÎĽg/
kg/hour from 4 to 24 hours (n = 9). In addition, one group
received rhAPC as above as the only intervention (n = 4), and
four sham-operated sheep were used for determination of the α
and ε isoforms of protein kinase C in pulmonary tissue. Data
were assessed by one-way analysis of variance for repeated
measurements. Biochemical data were analyzed using
Student's t test, or using the Mann–Whitney U test when
appropriate.
Results: Infusion of endotoxin caused lung injury, manifested by
increments in pulmonary artery pressure, in pulmonary microocclusion
pressure, in pulmonary vascular downstream
resistance, in pulmonary vascular permeability index, in
extravascular lung water index and in deterioration of
oxygenation that were all attenuated by infusion of rhAPC.
Endotoxemia led to changes in inflammation and coagulation,
including pulmonary neutrophil accumulation paralleled by
increased TNFα and decreased protein C and fibrinogen in
animal plasma, which all improved following infusion of rhAPC.
Moreover, rhAPC prevented the translocation of protein kinase
C α and ε isoforms from the cytosolic fraction of lung tissue
extracts.
Conclusion: In awake sheep, rhAPC alleviates endotoxininduced
lung injury – as characterized by improvements of
oxygenation, coagulation and inflammation, as well as by
reversal of pulmonary hemodynamic and volumetric changes
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Controls on inorganic nitrogen leaching from Finnish catchments assessed using a sensitivity and uncertainty analysis of the INCA -N model
The semi-distributed, dynamic INCA-N model was used to simulate the behaviour of dissolved inorganic nitrogen (DIN) in two Finnish research catchments. Parameter sensitivity and model structural uncertainty were analysed using generalized sensitivity analysis. The Mustajoki catchment is a forested upstream catchment, while the Savijoki catchment represents intensively cultivated lowlands. In general, there were more influential parameters in Savijoki than Mustajoki. Model results were sensitive to N-transformation rates, vegetation dynamics, and soil and river hydrology. Values of the sensitive parameters were based on long-term measurements covering both warm and cold years. The highest measured DIN concentrations fell between minimum and maximum values estimated during the uncertainty analysis. The lowest measured concentrations fell outside these bounds, suggesting that some retention processes may be missing from the current model structure. The lowest concentrations occurred mainly during low flow periods; so effects on total loads were small
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