1,053 research outputs found
Compounded perturbations in coastal areas: contrasting responses to nutrient enrichment and the regime of storm-related disturbance depend on life-history traits
1. Natural systems are exposed to compounded perturbations, whose changes in temporal
variance can be as important as those in mean intensity for shaping the structure of assemblages.
Specifically, climate-related physical disturbances and nutrient inputs due to natural
and/or anthropogenic activities occur concomitantly, but experimental tests of the simultaneous
effects of changes in the regime of more than one perturbation are generally lacking.
Filling this gap is the key to understand ecological responses of natural assemblages to
climate-related change in the intensity and temporal patterning of physical disturbance combined
with other global stressors.
2. Responses to factorial manipulations of nutrient enrichment, mean intensity and temporal
variability in storm-like mechanical disturbance were examined, using benthic assemblages of
tide-pools as model system.
3. Response variables were mean abundance values and temporal variances of taxa with different
life-traits. Consistent negative effects of disturbance intensity were observed for the mean
cover of long-living taxa (algal canopies and the polychaete Sabellaria alveolata), whose temporal
fluctuations were also reduced by more severe mechanical stress. More resilient taxa
(ephemeral algae, mostly green of the genus Ulva) increased under enriched conditions, particularly
when low-intensity events were irregularly applied over time. Opposite effects of disturbance
intensity depending on nutrient availability occurred on filamentous algae (e.g. red of
the genus Ceramium). This was probably due to the fact that, although nutrient enrichment
stimulated the abundance of both algal groups, when this condition was combined with relatively
mild physical disturbance the competitively superior ephemeral green algae tended to
become dominant over filamentous red algae. The same did not occur under high intensity of
disturbance since it likely damaged large, foliose fronds of Ulva-like forms more than small, filamentous
fronds of Ceramium-like forms. Grazers were positively affected by nutrients, likely
responding indirectly to more food available.
4. A direct relationship between the mean abundance of most organisms and their temporal
fluctuations was documented. However, all organisms persisted throughout the study, even
under experimental conditions associated to the largest temporal variation in their abundance,
likely due to their ability to resist to/quickly recover from, the applied perturbations. Therefore,
in systems with great recovery abilities of dominant organisms (e.g. rocky intertidal,
grasslands), effects of traits of the regime of disturbance and nutrient enrichment may modulate the fluctuations of populations not through the elimination and substitution of species,
but through changes in relative abundances of the same species. This contrasts with the
theory that temporal variation in abundance would be directly related to the risk of local
extinction. Present findings enable more accurate predictions of the consequences of climatic
and non-climatic scenarios on the biodiversity of marine and terrestrial systems sharing analogous
functional traits of organisms. Future more intense physical disturbances are expected to
exert negative effects on slow-growing/recovering species (e.g. habitat-formers) irrespectively of
the temporal patterning of the same disturbances and nutrient inputs. On the contrary, more
resistant species (e.g. encrusting algae on rocky shores or below-ground vegetation in grasslands)
are expected to benefit from intense physical disturbance. Species whose abundance is
more directly related to the availability of nutrients (e.g. filamentous and ephemeral algae or
herbs) are expected to generally increase under enriched conditions, but their ability to eventually
become dominant would depend on their ability to grow fast and attain cover large
enough to overwhelm any possible control of concomitant disturbance intensity on their abundance.
If, such as in the present examined system, virtually all organisms can persist, over the
temporal scale of the experiment, under any combination of physical disturbance and nutrient
availability, the resulting overall diversity is not predicted to change drastically. Nevertheless,
low-intensity events evenly distributed and high-intensity events irregularly distributed appear
as the conditions supporting the highest richness of taxa, independently of the availability of
nutrients
Edge magnetoplasmons in periodically modulated structures
We present a microscopic treatment of edge magnetoplasmons (EMP's) within the
random-phase approximation for strong magnetic fields, low temperatures, and
filling factor , when a weak short-period superlattice potential is
imposed along the Hall bar. The modulation potential modifies both the spatial
structure and the dispersion relation of the fundamental EMP and leads to the
appearance of a novel gapless mode of the fundamental EMP. For sufficiently
weak modulation strengths the phase velocity of this novel mode is almost the
same as the group velocity of the edge states but it should be quite smaller
for stronger modulation. We discuss in detail the spatial structure of the
charge density of the renormalized and the novel fundamental EMP's.Comment: 8 pages, 4 figure
Strange nucleon form factors in the perturbative chiral quark model
We apply the perturbative chiral quark model at one loop to calculate the
strange form factors of the nucleon. A detailed numerical analysis of the
strange magnetic moments and radii of the nucleon, and also the momentum
dependence of the form factors is presented.Comment: 18 pages, 6 figure
Precise evaluation of leaked information with universal2 privacy amplification in the presence of quantum attacker
We treat secret key extraction when the eavesdropper has correlated quantum
states. We propose quantum privacy amplification theorems different from
Renner's, which are based on quantum conditional R\'{e}nyi entropy of order
1+s. Using those theorems, we derive an exponential decreasing rate for leaked
information and the asymptotic equivocation rate, which have not been derived
hitherto in the quantum setting
Variation in The Vitamin D Receptor Gene is Associated With Multiple Sclerosis in an Australian Population
Multiple Sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS) resulting in accumulating neurological disability. The disorder is more prevalent at higher latitudes. To investigate VDR gene variation using three intragenic restriction fragment length polymorphisms (Apa I, Taq I and Fok I) in an Australian MS case-control population, one hundred and four Australian MS patients were studied with patients classified clinically as Relapsing Remitting MS (RR-MS), Secondary Progressive MS (SP-MS) or Primary Progressive MS (PP-MS). Also, 104 age-, sex-, and ethnicity-matched controls were investigated as a comparative group. Our results show a significant difference of genotype distribution frequency between the case and control groups for the functional exon 9 VDR marker Taq I (p_Gen = 0.016) and interestingly, a stronger difference for the allelic frequency (p_All = 0.0072). The Apa I alleles were also found to be associated with MS (p_All = 0.04) but genotype frequencies were not significantly different from controls (p_Gen = 0.1). The Taq and Apa variants are in very strong and significant linkage disequilibrium (D' = 0.96, P < 0.0001). The genotypic associations are strongest for the progressive forms of MS (SP-MS and PP-MS). Our results support a role for the VDR gene increasing
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
- …