282 research outputs found
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Effect of Biodiversity Changes in Disease Risk: Exploring Disease Emergence in a Plant-Virus System
The effect of biodiversity on the ability of parasites to infect their host and cause disease (i.e. disease risk) is a major question in pathology, which is central to understand the emergence of infectious diseases, and to develop strategies for their management. Two hypotheses, which can be considered as extremes of a continuum, relate biodiversity to disease risk: One states that biodiversity is positively correlated with disease risk (Amplification Effect), and the second predicts a negative correlation between biodiversity and disease risk (Dilution Effect). Which of them applies better to different host-parasite systems is still a source of debate, due to limited experimental or empirical data. This is especially the case for viral diseases of plants. To address this subject, we have monitored for three years the prevalence of several viruses, and virus-associated symptoms, in populations of wild pepper (chiltepin) under different levels of human management. For each population, we also measured the habitat species diversity, host plant genetic diversity and host plant density. Results indicate that disease and infection risk increased with the level of human management, which was associated with decreased species diversity and host genetic diversity, and with increased host plant density. Importantly, species diversity of the habitat was the primary predictor of disease risk for wild chiltepin populations. This changed in managed populations where host genetic diversity was the primary predictor. Host density was generally a poorer predictor of disease and infection risk. These results support the dilution effect hypothesis, and underline the relevance of different ecological factors in determining disease/infection risk in host plant populations under different levels of anthropic influence. These results are relevant for managing plant diseases and for establishing conservation policies for endangered plant species
Multi-Scale Sampling to Evaluate Assemblage Dynamics in an Oceanic Marine Reserve
To resolve the capacity of Marine Protected Areas (MPA) to enhance fish productivity it is first necessary to understand how environmental conditions affect the distribution and abundance of fishes independent of potential reserve effects. Baseline fish production was examined from 2002–2004 through ichthyoplankton sampling in a large (10,878 km2) Southern Californian oceanic marine reserve, the Cowcod Conservation Area (CCA) that was established in 2001, and the Southern California Bight as a whole (238,000 km2 CalCOFI sampling domain). The CCA assemblage changed through time as the importance of oceanic-pelagic species decreased between 2002 (La Niña) and 2003 (El Niño) and then increased in 2004 (El Niño), while oceanic species and rockfishes displayed the opposite pattern. By contrast, the CalCOFI assemblage was relatively stable through time. Depth, temperature, and zooplankton explained more of the variability in assemblage structure at the CalCOFI scale than they did at the CCA scale. CalCOFI sampling revealed that oceanic species impinged upon the CCA between 2002 and 2003 in association with warmer offshore waters, thus explaining the increased influence of these species in the CCA during the El Nino years. Multi-scale, spatially explicit sampling and analysis was necessary to interpret assemblage dynamics in the CCA and likely will be needed to evaluate other focal oceanic marine reserves throughout the world
Gate-tuning of graphene plasmons revealed by infrared nano-imaging
Surface plasmons are collective oscillations of electrons in metals or
semiconductors enabling confinement and control of electromagnetic energy at
subwavelength scales. Rapid progress in plasmonics has largely relied on
advances in device nano-fabrication, whereas less attention has been paid to
the tunable properties of plasmonic media. One such medium-graphene-is amenable
to convenient tuning of its electronic and optical properties with gate
voltage. Through infrared nano-imaging we explicitly show that common
graphene/SiO2/Si back-gated structures support propagating surface plasmons.
The wavelength of graphene plasmons is of the order of 200 nm at
technologically relevant infrared frequencies, and they can propagate several
times this distance. We have succeeded in altering both the amplitude and
wavelength of these plasmons by gate voltage. We investigated losses in
graphene using plasmon interferometry: by exploring real space profiles of
plasmon standing waves formed between the tip of our nano-probe and edges of
the samples. Plasmon dissipation quantified through this analysis is linked to
the exotic electrodynamics of graphene. Standard plasmonic figures of merits of
our tunable graphene devices surpass that of common metal-based structures.Comment: 15 pages, 3 figure
A comparison of metrics for estimating phylogenetic signal under alternative evolutionary models
Are Nested Networks More Robust to Disturbance? A Test Using Epiphyte-Tree, Comensalistic Networks
Recent research on ecological networks suggests that mutualistic networks are
more nested than antagonistic ones and, as a result, they are more robust
against chains of extinctions caused by disturbances. We evaluate whether
mutualistic networks are more nested than comensalistic and antagonistic
networks, and whether highly nested, host-epiphyte comensalistic networks fit
the prediction of high robustness against disturbance. A review of 59 networks
including mutualistic, antagonistic and comensalistic relationships showed that
comensalistic networks are significantly more nested than antagonistic and
mutualistic networks, which did not differ between themselves. Epiphyte-host
networks from old-growth forests differed from those from disturbed forest in
several topological parameters based on both qualitative and quantitative
matrices. Network robustness increased with network size, but the slope of this
relationship varied with nestedness and connectance. Our results indicate that
interaction networks show complex responses to disturbances, which influence
their topology and indirectly affect their robustness against species
extinctions
Estimating how inflated or obscured effects of climate affect forecasted species distribution
Climate is one of the main drivers of species distribution. However, as different environmental factors tend to co-vary, the
effect of climate cannot be taken at face value, as it may be either inflated or obscured by other correlated factors. We used
the favourability models of four species (Alytes dickhilleni, Vipera latasti, Aquila fasciata and Capra pyrenaica) inhabiting
Spanish mountains as case studies to evaluate the relative contribution of climate in their forecasted favourability by using
variation partitioning and weighting the effect of climate in relation to non-climatic factors. By calculating the pure effect of
the climatic factor, the pure effects of non-climatic factors, the shared climatic effect and the proportion of the pure effect of
the climatic factor in relation to its apparent effect (r), we assessed the apparent effect and the pure independent effect of
climate. We then projected both types of effects when modelling the future favourability for each species and combination
of AOGCM-SRES (two Atmosphere-Ocean General Circulation Models: CGCM2 and ECHAM4, and two Special Reports on
Emission Scenarios (SRES): A2 and B2). The results show that the apparent effect of climate can be either inflated (overrated)
or obscured (underrated) by other correlated factors. These differences were species-specific; the sum of favourable areas
forecasted according to the pure climatic effect differed from that forecasted according to the apparent climatic effect by
about 61% on average for one of the species analyzed, and by about 20% on average for each of the other species. The pure
effect of future climate on species distributions can only be estimated by combining climate with other factors. Transferring
the pure climatic effect and the apparent climatic effect to the future delimits the maximum and minimum favourable areas
forecasted for each species in each climate change scenario.Ministerio de Ciencia e Innovación and FEDER (project CGL2009-11316/BOS). D. Romero is a PhD student at the University of Malaga with a grant of the Ministerio de Educacio´n y Ciencia (AP 2007-03633
Stability of gene contributions and identification of outliers in multivariate analysis of microarray data
BACKGROUND: Multivariate ordination methods are powerful tools for the exploration of complex data structures present in microarray data. These methods have several advantages compared to common gene-by-gene approaches. However, due to their exploratory nature, multivariate ordination methods do not allow direct statistical testing of the stability of genes. RESULTS: In this study, we developed a computationally efficient algorithm for: i) the assessment of the significance of gene contributions and ii) the identification of sample outliers in multivariate analysis of microarray data. The approach is based on the use of resampling methods including bootstrapping and jackknifing. A statistical package of R functions was developed. This package includes tools for both inferring the statistical significance of gene contributions and identifying outliers among samples. CONCLUSION: The methodology was successfully applied to three published data sets with varying levels of signal intensities. Its relevance was compared with alternative methods. Overall, it proved to be particularly effective for the evaluation of the stability of microarray data
New approaches to high-resolution mapping of marine vertical structures
Vertical walls in marine environments can harbour high biodiversity and provide natural protection from bottom-trawling activities. However, traditional mapping techniques are usually restricted to down-looking approaches which cannot adequately replicate their 3D structure. We combined sideways-looking multibeam echosounder (MBES) data from an AUV, forward-looking MBES data from ROVs and ROV-acquired videos to examine walls from Rockall Bank and Whittard Canyon, Northeast Atlantic. High-resolution 3D point clouds were extracted from each sonar dataset and structure from motion photogrammetry (SfM) was applied to recreate 3D representations of video transects along the walls. With these reconstructions, it was possible to interact with extensive sections of video footage and precisely position individuals. Terrain variables were derived on scales comparable to those experienced by megabenthic individuals. These were used to show differences in environmental conditions between observed and background locations as well as explain spatial patterns in ecological characteristics. In addition, since the SfM 3D reconstructions retained colours, they were employed to separate and quantify live coral colonies versus dead framework. The combination of these new technologies allows us, for the first time, to map the physical 3D structure of previously inaccessible habitats and demonstrates the complexity and importance of vertical structures
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