1,242 research outputs found
Genetic diversity in brackish-water environments as revealed by mitochondrial markers in three species with different ecological traits
In the present study, the genetic diversity of brackish water environments was studied analysing three model species with different ecological traits by mean of mitochondrial genes sequences. In the first model species, Hediste diversicolor (O.F. Müller, 1776) (Annelida, Polychaeta), a portion of the COI gene (544 bp) was amplifyed in 181 individuals from nine population, two from the Atlantic ocean, and seven from Western Mediterranean. In Mytilaster minimus (Poli, 1795) (Mollusca, Bivalvia), the second analysed species, a fragment of the 16S gene (445 bp) was amplifyed in 25 individuals from five populations in the Mediterranean Sea, two sampled in marine sites, three sampled in brackish-water sites. The third model species is Xenostrobus securis (Lam., 1819) (Mollusca, Bivalvia), original of southern Australia and New Zealand estuaries. In the latter species, a fragment of the COI gene (564 bp) was amplifyed in 39 individuals from five recently settled populations in the Mediterranean Sea.
Analysis of the data collected from the three species yielded different phylogeographycal patterns. H. diversicolor showed a deep genetic structure, and a hierarchical organisation of genetic diversity on different spatial scales. These features were related to the effect of a major phylogeographical break between Atlantic and Meediterranean, and, inside each basin, to habitat fragmentation and scarce levels of gene flow given the lack of a dispersal stage. M. minimus revealed the presence of three partly sympatric lineages, and a strong genetic divergence between populations from marine- and brackish-water habitats, maybe due to the effects of different selective pressure in the two environmental typology. X. securis was characterised by high levels of within-population genetic diversity, presence of sympatric divergent lineages, and total absence of genetic structure among the sampled populations. The absence of genetic divergence among populations is to relate to their recent settling, no more than 20 years ago.
Levels of genetic divergence encountered in this study amond different populations and among different habitats evidenced the heterogeneity of brackish water environments and the effects that thiss heterogeneity exerts on organism. As a consequence, the managment of such biotopes needs to be finely tuned from case to case and cannot rely on general assumpionts
The Higgs mass as a function of the compactification scale
We calculate to a few percent precision the Higgs potential in a model with
supersymmetry broken by boundary conditions on an extra-dimension, compactified
to a segment of length , and a top quark quasi-localized on one of the two
boundaries. 1/L alone, in the range 2-4 TeV, determines the Higgs mass, in the
range 110-125 GeV, and the spectrum of gauginos, higgsinos and of the
third-generation squarks. Lower values of 1/L cannot be excluded, with a
progressive delocalization of the top quark.Comment: 22 pages, 6 figure
Radiative Electroweak Symmetry Breaking from a Quasi-Localized Top Quark
We consider 5D supersymmetric SU(3) x SU(2) x U(1) theories compactified at
the TeV scale on S^1/Z_2 with supersymmetry broken by boundary conditions.
Localizing the top quark at a boundary of a fifth dimension by a bulk mass term
M_t, reduces the strength of radiative electroweak symmetry breaking. For M_t R
approximately 1--2, the natural value for the top and bottom squark masses are
raised to 500--1200 GeV, and all other superpartners may have masses of the
compactification scale, which has a natural range of 1/R ~= 1.5--3.5 TeV. The
superpartner masses depend only on 1/R, and are precisely correlated amongst
themselves and with the mass of the Higgs boson, which is lighter than 130 GeV.Comment: 23 pages, 8 figures, Latex; typos correcte
Speed of qubit states during thermalisation
Classifying quantum states usually demands to observe properties such as the
amount of correlation at one point in time. Further insight may be gained by
inspecting the dynamics in a given evolution scheme. Here we attempt such a
classification looking at single-qubit and two-qubit states at the start of
thermalisation with a heat bath. The speed with which the evolution starts is
influenced by quantum aspects of the state, however, such signatures do not
allow for a systematic classification
Breaking the electroweak symmetry and supersymmetry by a compact extra dimension
We revisit in some more detail a recent specific proposal for the breaking of
the electroweak symmetry and of supersymmetry by a compact extra dimension.
Possible mass terms for the Higgs and the matter hypermultiplets are considered
and their effects on the spectrum analyzed. Previous conclusions are reinforced
and put on firmer ground.Comment: 25 pages, LaTeX, 9 eps figure
Modelling of multiscale nonlinear interaction of elastic waves with three-dimensional cracks
This paper presents a nonlinear elastic material model able to simulate the nonlinear effects generated by the interaction of acoustic/ultrasonic waves with damage precursors and micro-cracks in a variety of materials. Such a constitutive model is implemented in an in-house finite element code and exhibits a multiscale nature where the macroscopic behavior of damaged structures can be represented through a contribution of a number of mesoscopic elements, which are composed by a statistical collection of microscopic units. By means of the semi-analytical Landau formulation and Preisach-Mayergoyz space representation, this multiscale model allows the description of the structural response under continuous harmonic excitation of micro-damaged materials showing both anharmonic and dissipative hysteretic effects. In this manner, nonlinear effects observed experimentally, such as the generation of both even and odd harmonics, can be reproduced. In addition, by using Kelvin eigentensors and eigenelastic constants, the wave propagation problem in both isotropic and orthotropic solids was extended to the three-dimensional Cartesian space. The developed model has been verified for a number of different geometrical and material configurations. Particularly, the influence of a small region with classical and non-classical elasticity and the variations of the input amplitudes on the harmonics generation were analyzed
Precise optical timing of PSR J1023+0038, the first millisecond pulsar detected with Aqueye+ in Asiago
We report the first detection of an optical millisecond pulsar with the fast
photon counter Aqueye+ in Asiago. This is an independent confirmation of the
detection of millisecond pulsations from PSR J1023+0038 obtained with SiFAP at
the Telescopio Nazionale Galileo. We observed the transitional millisecond
pulsar PSR J1023+0038 with Aqueye+ mounted at the Copernicus telescope in
January 2018. Highly significant pulsations were detected. The rotational
period is in agreement with the value extrapolated from the X-ray ephemeris,
while the time of passage at the ascending node is shifted by
s from the value predicted using the orbital period from the X-rays. An
independent optical timing solution is derived over a baseline of a few days,
that has an accuracy of in pulse phase ( s in time).
This level of precision is needed to derive an accurate coherent timing
solution for the pulsar and to search for possible phase shifts between the
optical and X-ray pulses using future simultaneous X-ray and optical
observations.Comment: 6 pages, 4 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
fabrication and characterization of an innovative heat exchanger with open cell aluminum foams
Abstract: The present study deals with the design, the fabrication and the characterization of an innovative heat exchanger manufactured by using open cell aluminum foams. The cooling performances of the heat exchanger, working in low temperature difference were measured. Open cells aluminum foams, produced via polymeric foam replication method, have been assembled to manufacture the cooling elements. The wettability of the aluminum foam surface was improved through a surface treatment, in order to enhance the joining between the pipes and the metal foam. In a first phase, preliminary experimental tests on aluminum metal foam samples were used for an estimation of the overall cooling performance. The experimental test was also aimed to understand the basic mechanisms involved in the heat transfer process. In a second phase, the full heat exchanger was assembled, and an experimental setup was designed in order to determine the performance of the heat exchanger. The heat exchanger revealed its high potentiality in terms of thermal performance, showing also a remarkable behavior in terms of energy saving, assembly and endurance
A contribution to the phylogeography of Pinctada imbricata radiata (Leach, 1814) (Bivalvia: Pteriidae) from the Eastern Mediterranean Sea by means of the mitochondrial COI marker
Pinctada imbricata radiata (Leach, 1814) was the first Lessepsian bivalve reported in the Mediterranean Sea where it is progressively expanding westward. Its native range includes the Indian Ocean and western Atlantic. The present study provides the first insight into the species’ phylogeographic structure, by analysing sequences of a 385-bp region of the mitochondrial gene coding for the subunit I of the cytochrome c oxydase (COI). Sixty-four individuals collected at seven Mediterranean localities were sequenced; in addition, eight COI sequences of individuals from the species’ native range (Persian Gulf) were retrieved from GenBank. Overall, we detected 10 haplotypes. Samples from both the native range and invaded localities were characterised by low levels of haplotype and nucleotide diversity (total h = 0.351, total π = 0.0013). Significant genetic divergence was found between Persian Gulf and Mediterranean Sea samples, whereas very shallow genetic structuring was observed within the Mediterranean study area. Moreover, no pattern of isolation by distance was detected in the Mediterranean. From a historical demography perspective, our results on Mediterranean samples were consistent with a very recent, or even ongoing, demographic expansion. Range expansion of exotic thermophilic species in this area is a widely observed phenomenon that many authors have related to global warming
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