469 research outputs found
Toxicity of various silver nanoparticles compared to silver ions in the Ponto-Caspian amphipod Pontogammarus maeoticus (Sowinsky, 1894)
According to the increased probability of the presence of nanomaterials in the aquatic ecosystems, the present study examined the toxicity of three engineered silver nanoparticles (AgNPs) as well as silver ions in the Pontogammarus maeoticus, a brackish water benthic organism living in the littoral zone of the Caspian Sea. The animals were acutely exposed to different concentrations of two commercially prepared colloidal forms and a freshly prepared suspension of silver nanoparticles, plus AgNO3 during 48 hr. The number of mortalities was assessed and lethal concentration values were calculated using the EPA Probit Analysis Program. According to median lethal concentrations (LC50), the order of sensitivity of this amphipod to tested silver compounds was as: previously prepared AgNPs colloids > freshly prepared AgNPs suspension > AgNO3. Also the signs of nanoparticle accumulation were evident between the pereopods and pleopods of this gammarid; this accumulation could be one of the reasons for the higher toxicity of silver nanoparticles in comparison with silver ions in P. maeoticus. More acute and chronic studies are needed to understand the various aspects of nano-silver toxicity on amphipods in different salinities
Toxicity comparison of silver nanoparticles synthesized by physical and chemical methods to tadpole (Rana ridibunda)
One of the possible threats in increasing use of nanomaterials is the emergence of toxicity in humans and other animals which is discussed in nanotoxicology. In addition to toxic effects of nanomaterials themselves, different chemical precursors which are usually used in bottom-up approaches for production of nanomaterials may have secondary toxic effects in living organisms. In contrast, less use of chemicals in top-down approaches may reduce these secondary effects. To test this hypothesis, toxic effects of two types of silver nanoparticles (AgNPs) produced by physical (top-down) and chemical (bottom-up) methods were investigated and compared on the tadpole, Rana ridibunda survival. The estimated 48 h LC50 values of AgNPs produced by chemical and physical methods for tadpoles were 0.055 ± 0.004 and 0.296 ± 0.085 mg.L-1, respectively. No observed effect concentration, lowest observed effect concentration, maximum acceptable toxicant concentration and median lethal concentration of AgNPs produced by chemical method were respectively 3.42, 4.50, 4.84 and 5.38 times less than those produced by physical method. Therefore, approving the mentioned hypothesis, it was revealed that AgNPs produced by chemical method are more toxic than those generated by physical method. However, it seems totally that AgNPs regardless of the method used for their production, have toxic effects on aquatic organisms and so, inhibiting their accidental or intentional entrance into the aquatic ecosystems should be more considered
Palliative care in dementia: literaturereview of nursesâ knowledge andattitudes towards pain assessment
High resolution simulations of unstable modes in a collisionless disc
We present N-body simulations of unstable spiral modes in a dynamically cool
collisionless disc. We show that spiral modes grow in a thin collisionless disk
in accordance with the analytical perturbation theory. We use the particle-mesh
code SUPERBOX with nested grids to follow the evolution of unstable spirals
that emerge from an unstable equilibrium state. We use a large number of
particles (up to 40 million particles) and high-resolution spatial grids in our
simulations (128^3 cells). These allow us to trace the dynamics of the unstable
spiral modes until their wave amplitudes are saturated due to nonlinear
effects. In general, the results of our simulations are in agreement with the
analytical predictions. The growth rate and the pattern speed of the most
unstable bar-mode measured in N-body simulations agree with the linear
analysis. However the parameters of secondary unstable modes are in lesser
agreement because of the still limited resolution of our simulations.Comment: 11 pages, 8 figures in 22 files, A&A in print: Oct. 1st 200
Discovery and genotyping of novel sequence insertions in many sequenced individuals
Motivation: Despite recent advances in algorithms design to characterize structural variation using high-throughput short read sequencing (HTS) data, characterization of novel sequence insertions longer than the average read length remains a challenging task. This is mainly due to both computational difficulties and the complexities imposed by genomic repeats in generating reliable assemblies to accurately detect both the sequence content and the exact location of such insertions. Additionally, de novo genome assembly algorithms typically require a very high depth of coverage, which may be a limiting factor for most genome studies. Therefore, characterization of novel sequence insertions is not a routine part of most sequencing projects. There are only a handful of algorithms that are specifically developed for novel sequence insertion discovery that can bypass the need for the whole genome de novo assembly. Still, most such algorithms rely on high depth of coverage, and to our knowledge there is only one method (PopIns) that can use multi-sample data to "collectively" obtain a very high coverage dataset to accurately find insertions common in a given population. Result: Here, we present Pamir, a new algorithm to efficiently and accurately discover and genotype novel sequence insertions using either single or multiple genome sequencing datasets. Pamir is able to detect breakpoint locations of the insertions and calculate their zygosity (i.e. heterozygous versus homozygous) by analyzing multiple sequence signatures, matching one-end-anchored sequences to small-scale de novo assemblies of unmapped reads, and conducting strand-aware local assembly. We test the efficacy of Pamir on both simulated and real data, and demonstrate its potential use in accurate and routine identification of novel sequence insertions in genome projects. © 2017 The Author. Published by Oxford University Press. All rights reserved
Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208
We have undertaken a thorough dynamical investigation of five extrasolar
planetary systems using extensive numerical experiments. The systems Gl 777 A,
HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of
whether they could host terrestrial like planets in their habitable zones
(=HZ). First we investigated the mean motion resonances between fictitious
terrestrial planets and the existing gas giants in these five extrasolar
systems. Then a fine grid of initial conditions for a potential terrestrial
planet within the HZ was chosen for each system, from which the stability of
orbits was then assessed by direct integrations over a time interval of 1
million years. The computations were carried out using a Lie-series integration
method with an adaptive step size control. This integration method achieves
machine precision accuracy in a highly efficient and robust way, requiring no
special adjustments when the orbits have large eccentricities. The stability of
orbits was examined with a determination of the Renyi entropy, estimated from
recurrence plots, and with a more straight forward method based on the maximum
eccentricity achieved by the planet over the 1 million year integration.
Additionally, the eccentricity is an indication of the habitability of a
terrestrial planet in the HZ; any value of e>0.2 produces a significant
temperature difference on a planet's surface between apoapse and periapse. The
results for possible stable orbits for terrestrial planets in habitable zones
for the five systems are summarized as follows: for Gl 777 A nearly the entire
HZ is stable, for 47 Uma, HD 72659 and HD 4208 terrestrial planets can survive
for a sufficiently long time, while for Gl 614 our results exclude terrestrial
planets moving in stable orbits within the HZ.Comment: 14 pages, 18 figures submitted to A&
Making Associativity Operational
The purpose of this paper is to propose an operational idea for developing algebraic thinking in the absence of alphanumeric symbols. The paper reports on a design experiment encouraging preschool children to use the associative property algebraically. We describe the theoretical basis of the design, the tasks used, and examples of algebraic thinking in 5â6-year-old children. Theoretically, the paper makes a critical distinction between operational and structural meanings of the notion of equality. We argue that mathematical thinking involving equality among young learners can comprise both an operational and a structural conception and that the operational conception has a side that is productively linked to the structural conception. Using carefully designed hands-on tasks, the crux of the paper is the realization of algebraic thinking (in verbal mathematics) as operationally experienced in the ability to transform one number structure, with a quantity that is subject to change, into another through equality-preserving transformations
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Phase-matched multi-layer based polarisation-independent spot-size converter for silicon nanowire
The efficient coupling of optical power from a silicon nanowire (NW) to an optical fibre is challenging for both the quasi-TE and quasi-TM polarisations. Here, we propose a polarisation-independent spot-size converter (PI-SSC) based on phase-matched multi-layer waveguides for efficient coupling between a silicon NW and an optical fibre for both the polarisations. The fabrication process of the proposed PI-SSC is compatible with the complementary metal-oxide-semiconductor (CMOS) process. The optimisation for the proposed PI-SSC is studied by using a numerically efficient algorithm, combining a rigorous H-field based full-vectorial finite element method (VFEM) and the least squares boundary residual (LSBR) method. The simulation results show that using an eleven-layer based PI-SSC, the coupling losses between a silicon NW and a lensed fibre of radius 2 ÎŒm can be reduced to only 0.34 dB and 0.25 dB for the quasi-TE and quasi-TM polarisations, respectively. Furthermore, the output multi-layer is horizontally tapered, which further reduces the coupling loss for both the polarisations and the end face is easy to be polished
Laimaphelenchus suberensis sp. nov. associated with Quercus suber in Portugal
Laimaphelenchus suberensis sp. nov. obtained
from declining Quercus suber trees of Herdade da
Gouveia de Baixo, Alentejo, Portugal, is described and
illustrated based on morphological, biometrical and molecular
characters. The diagnosis of Laimaphelenchus
species has been commonly based on the presence or
absence of a vulval flap and on the shape structure of the
tail tip. The species described here has been included in
the Laimaphelenchus group without vulval flap, and can
be distinguished from morphologically similar species
by its tail tip shape structure that has a stalk-like terminus
and three diffuse tubercles with 4â6 finger-like
protrusions. For the molecular analyses, the mitochondrial
DNA region from the cytochrome oxidase subunit
I (mtCOI), the D2-D3 expansion segments of the large
subunit (LSU) and small subunit (SSU) of rRNA gene
were amplified and sequenced. Sequences of
L. suberensis sp. nov. clustered separately from all
Laimaphelenchus spp. with available sequences in
Genbank, confirming its identification as a new species.
This is the second report of the genus Laimaphelenchus
in Portugal, associated with Q. suber: L. heidelbergi and
L. suberensis sp. nov.This research was supported by CFE,
CIEPQPF and FEDER funds through the âPrograma Operacional
Factores de Competitividade â COMPETEâ and by national funds
through FCTâFundação para a CiĂȘncia e a Tecnologia under the
projects UID/BIA/04004/2013, PEst-C/EQB/UI0102/2013 and
FCOMP-01-0124-008937 (Ref. PTDC/BIAâBEC/102834/2008)
and by Instituto do Ambiente, Tecnologia e Vida (IATV). Carla
Maleita (SFRH/BPD/85736/2012) and Sofia Costa (SFRH/BPD/
102438/2014) were financed by MEC National funding and The
European Social Fund through POCH (Programa Operacional
Capital Humano).info:eu-repo/semantics/publishedVersio
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