Search results for "Extinction"
showing 10 items of 458 documents
Mode cleaning in graphene oxide-doped polymeric whispering gallery mode microresonators
2020
The strategy to incorporate graphene oxide (GO) in a composite material offers significant opportunities to realize compact photonic devices, such as saturable absorbers and polarization selective devices. However, the processing of GO-based composites by direct laser writing, which would afford vast patterning and material flexibility in a single step process, has been little addressed. In this work, we investigated the mechanisms underlying a mode cleaning effect in polymeric whispering gallery mode microresonators containing GO, aiming at the development of on-chip integrable photonic devices. We fabricated the microresonators (cavity loaded Q-factor of 20 000 at 1550 nm) in a single ste…
ANCAMAN DAN KEPUNAHAN BURUNG MAMBRUK POLOS Goura cristata DI BAGIAN TIMUR KEPALA BURUNG (VOGELKOP) IRIAN JAYA BARAT
2008
<p><em>The three species of “mambruk” (crowned pidgeons) are endemic to New Guinea (Irian Jaya and the Papua Nugini). The species are listed in CITES as vulnerable. In Indonesia the species are protected by law, but in the field they are still being hunted. There fore, the threat and extinction of the species was observed on five location in the Birds Head Region of Papua. The observation indicated thet there was only are location was the estuary of Warmiseru and Suandei Lagoon where the spesies were relativety observed.</em></p>
TESTING SIMILARITY COEFFICIENTS FOR ANALYSIS OF THE FOSSIL RECORD USING CLUSTERING METHODS: THE PALAEOZOIC FLORA AS A STUDY CASE
2020
This paper reports a global methodological approach based on the similarity and clustering methods of the Palaeozoic plant fossil record using a comparative approach between two similarity measures: the Jacard and Raup-Crick Coefficients. The results show that although the Raup-Crick Coefficients clearly have the potential for providing more robust results, the consequences of the extinction processes are better reflected in the similarity analysis based on the Jaccard Coefficients. On the other hand, the cluster analysis based on UPGMA algorithm shows four robust clusters and reveals new evidence for the singularity of Mississippian flora. Finally, the results obtained reveal that similari…
Asymptotic regime in N random interacting species
2005
The asymptotic regime of a complex ecosystem with \emph{N}random interacting species and in the presence of an external multiplicative noise is analyzed. We find the role of the external noise on the long time probability distribution of the i-th density species, the extinction of species and the local field acting on the i-th population. We analyze in detail the transient dynamics of this field and the cavity field, which is the field acting on the $i^{th}$ species when this is absent. We find that the presence or the absence of some population give different asymptotic distributions of these fields.
Noise Induced Phenomena in Lotka-Volterra Systems
2003
We study the time evolution of two ecosystems in the presence of external noise and climatic periodical forcing by a generalized Lotka-Volterra (LV) model. In the first ecosystem, composed by two competing species, we find noise induced phenomena such as: (i) quasi deterministic oscillations, (ii) stochastic resonance, (iii) noise delayed extinction and (iv) spatial patterns. In the second ecosystem, composed by three interacting species (one predator and two preys), using a discrete model of the LV equations we find that the time evolution of the spatial patterns is strongly dependent on the initial conditions of the three species.
Combined effect of turbulence and aerosol on free-space optical links
2017
[EN] Despite the benefits of free-space optical (FSO) communications, their full utilization is limited by the influence of atmospheric weather conditions, such as fog, turbulence, smoke, snow, etc. In urban environments, additional environmental factors such as smog and dust particles due to air pollution caused by industry and motor vehicles may affect FSO link performance, which has not been investigated in detail yet. Both smog and dust particles cause absorption and scattering of the propagating optical signal, thus resulting in high attenuation. This work investigates the joint impact of atmospheric turbulence and dust particle-imposed scattering on FSO link performance as part of the…
A new giant ground bird from the Upper Cretaceous of southern France
1998
New discoveries afford a much better knowledge of the large birds previously reported from the Upper Cretaceous of southern France on the basis of a single synsacrum fragment. An incomplete pelvis consisting of the synsacrum with part of the ilia is used to define a new taxon of bird, Gargantuavis philoinos , to which a femur is also referred. This bird is characterized by its very large size (comparable to that of an ostrich), a broad pelvis with an anteriorly placed acetabulum, and a short robust femur. The occurrence of this very large, flightless, bird in the Late Cretaceous shows that, contrary to widespread opinion, the evolution of large terrestrial birds was not simply the result of…
Conditioned place preference paradigm can be a mouse model of relapse to opiates
2001
With the object of determining the usefulness of the conditioned place preference (CPP) paradigm as a model of relapse to opiates, the effects of the re-exposure to morphine are explored in male mice which had undergone a process of extinction of conditioning. Morphine (40 mg/kg) produces a CPP which lasts up to 15 days after conditioning. When it has completely extinguished (45 days), a non contingent re-exposure to the drug again produces the same preference. These results suggest that the CPP paradigm may be used in mice to study the mechanisms of relapse to opiates in addicts.
Effects of Hippocampal State-Contingent Trial Presentation on Hippocampus-Dependent Nonspatial Classical Conditioning and Extinction
2014
Hippocampal local field potentials are characterized by two mutually exclusive states: one characterized by regular θ oscillations (∼4–8 Hz) and the other by irregular sharp-wave ripples. Presenting stimuli during dominant θ oscillations leads to expedited learning, suggesting that θ indexes a state in which encoding is most effective. However, ripple-contingent training also expedites learning, suggesting that any discrete brain state, much like the external context, can affect learning. We trained adult rabbits in trace eyeblink conditioning, a hippocampus-dependent nonspatial task, followed by extinction. Trials were delivered either in the presence or absence of θ or regardless of hippo…
Cryptic biodiversity loss linked to global climate change
2011
Climate impacts on biodiversity are usually assessed at the morphospecies level. An analysis of the distribution and mitochondrial DNA variability of nine montane aquatic insect species in Europe suggests range contractions will be accompanied by severe loss of genetic diversity. These results imply that morphospecies-scale assessments may greatly underestimate potential biodiversity losses from climate change.