456 research outputs found
Electrical noise properties in aging materials
The electric thermal noise has been measured in two aging materials, a
colloidal suspension (Laponite) and a polymer (polycarbonate), presenting very
slow relaxation towards equilibrium. The measurements have been performed
during the transition from a fluid-like to a solid-like state for the gel and
after a quench for the polymer. For both materials we have observed that the
electric noise is characterized by a strong intermittency, which induces a
large violation of the Fluctuation Dissipation Theorem (FDT) during the aging
time, and may persist for several hours at low frequency. The statistics of
these intermittent signals and their dependance on the quench speed for the
polymer or on sample concentration for the gel are studied. The results are in
a qualitative agreement with recent models of aging, that predict an
intermittent dynamics.Comment: SPIE Proceeding Journa
Micronucleus test in erythrocytes of Barbus plebejus (Teleostei, Pisces) from two natural environments: A bioassay for the in situ detection of mutagens in freshwater
Erythrocyte micronucleus frequencies in wild fish from two riverine environments and in fish reproduced and reared under controlled conditions (control group) were compared, with the aim to evaluate the suitability of the MN test for the in situ detection of mutagens in freshwaters. Fish were caught in different months in two rivers of central ItaIy which have different pollution levels. As indicator species, the barbel (Barbus plebejus) was chosen because of its ecological significance. Blood samplings wen performed on wild fish immediately after capture and repeated at different time intervals on the same individuals, which were maintained in controlled conditions after capture. A total of 10,000 erythrocytes per specimen were scored. No significant differences in micronucleus frequencies were observed between the control group and fish from the unpolluted river (Mignone). A significantly higher frequency of micronuclei was observed in fish caught in the polluted river (Tibet), in comparison to both the controls and the Mignone river fish. No significant seasonal differences were observed. Barbels examined 50 and 100 days after capture presented a remarkable decrease in micronucleus frequency in comparison with the frequency observed in barbels at capture. The micronucleus test in fish erythrocytes was shown to be a sensitive bioassay for detecting mutagenic pollution in fresh water environments
Imaging the stick-slip peeling of an adhesive tape under a constant load
Using a high speed camera, we study the peeling dynamics of an adhesive tape
under a constant load with a special focus on the so-called stick-slip regime
of the peeling. It is the first time that the very fast motion of the peeling
point is imaged. The speed of the camera, up to 16000 fps, allows us to observe
and quantify the details of the peeling point motion during the stick and slip
phases: stick and slip velocities, durations and amplitudes. First, in contrast
with previous observations, the stick-slip regime appears to be only transient
in the force controlled peeling. Additionally, we discover that the stick and
slip phases have similar durations and that at high mean peeling velocity, the
slip phase actually lasts longer than the stick phase. Depending on the mean
peeling velocity, we also observe that the velocity change between stick and
slip phase ranges from a rather sudden to a smooth transition. These new
observations can help to discriminate between the various assumptions used in
theoretical models for describing the complex peeling of an adhesive tape. The
present imaging technique opens the door for an extensive study of the velocity
controlled stick-slip peeling of an adhesive tape that will allow to understand
the statistical complexity of the stick-slip in a stationary case
Hidden Order in Crackling Noise during Peeling of an Adhesive Tape
We address the long standing problem of recovering dynamical information from
noisy acoustic emission signals arising from peeling of an adhesive tape
subject to constant traction velocity. Using phase space reconstruction
procedure we demonstrate the deterministic chaotic dynamics by establishing the
existence of correlation dimension as also a positive Lyapunov exponent in a
mid range of traction velocities. The results are explained on the basis of the
model that also emphasizes the deterministic origin of acoustic emission by
clarifying its connection to sticks-slip dynamics.Comment: 5 pages, 10 figure
Exploring the conformational dynamics of alanine dipeptide in solution subjected to an external electric field: A nonequilibrium molecular dynamics simulation
In this paper, we investigate the conformational dynamics of alanine
dipeptide under an external electric field by nonequilibrium molecular dynamics
simulation. We consider the case of a constant and of an oscillatory field. In
this context we propose a procedure to implement the temperature control, which
removes the irrelevant thermal effects of the field. For the constant field
different time-scales are identified in the conformational, dipole moment, and
orientational dynamics. Moreover, we prove that the solvent structure only
marginally changes when the external field is switched on. In the case of
oscillatory field, the conformational changes are shown to be as strong as in
the previous case, and non-trivial nonequilibrium circular paths in the
conformation space are revealed by calculating the integrated net probability
fluxes.Comment: 23 pages, 12 figure
Fish response to multiple anthropogenic stressors in mediterranean coastal lagoons: A comparative study of the role of different management strategies
Transitional waters are among the most productive ecosystems of the world and their biotic communities show high diversity and complex mechanisms of self-regulation that provide valuable ecosystem services and societal goods and benefits. In this work a comparison of the fish assemblages of three non-tidal Mediterranean coastal lagoons is carried out in order to evaluate the impacts of alternative management strategies. The anthropogenic pressures acting on the lagoons were quantified by means of categorical indicators, while the characteristics of the fish assemblages were summarized in multi-metric indices (MMIs). Two MMIs were developed using data collected with a beach seine net and with fyke nets, following an empirical approach that selects, from a pool of 73 metrics, the combination that maximizes the MMI/pressure relationship. The two MMIs include four metrics each, most of which are based on feeding mode functional guilds and habitat use functional guilds, and they are sensitive to anthropogenic pressures. The human activities directly or indirectly affecting water quality are the ones that most influence the fish assemblage, while the presence of artisanal fisheries, a typical and relevant resource use in these lagoons, seems to play a beneficial role. Lagoon fisheries management relies on the maintenance of infrastructures that guarantee the hydraulic functioning of the lagoon, thus ensuring exchanges with the adjacent coastal sea, and therefore indirectly contributing to the habitat quality
In vitro screening of interspecific hybrids (Malus spp.) for resistance to apple proliferation
A breeding programme was set up six years ago in Trentino as part of the Project “Scopazzi del Melo - Apple Proliferation” (SMAP) in order to obtain AP resistant apple rootstocks.Twenty-six hybrids generated from the crossings (Malus sieboldii, second generation, x Malus domestica) were micropropagated and studied in standardised conditions. An in vitro screening system for AP resistance previously set for the parents of the crosses was adopted and modified. Specific symptoms of the disease, as well as height and basal proliferation of the shoot and size of the leaves, were recorded in vitro at 3 months post-inoculation. At the same time, phytoplasma concentration was determined in the whole shoot by quantitative RT-PCR. An in vitro disease index taking into account all the above-mentioned parameters was developed.Each healthy genotype was graft-inoculated in triplicate with two different phytoplasma strains after plant rooting and acclimatisation. Phenotype and phytoplasma titre were evaluated in the roots the year after infection.Preliminary results indicated that the resistance trait segregates in the progenies. The resistant genotypes had lower phytoplasma concentrations than the susceptible controls, did not show AP-specific symptoms and their growth was not affected by infection. By comparing the resistant behaviour of the same genotypes, the in vitro screening allows for a quick selection of genotypes that are worth evaluating in the field for agronomic traits.Keywords: Apple Proliferation, Malus sieboldii, resistance screening, quantitative real-time PCR, disease inde
Fast Simulation of Polymer Chains
We propose an algorithm for the fast and efficient simulation of polymers represented by chains of hard spheres. The particles are linked by holonomic bond constraints. While the motion of the polymers is free (i.e., no collisions occur) the equations of motion can be easily integrated using a collocation-based partitioned Gauss–Runge–Kutta method. The method is reversible, symplectic, and preserves energy. Moreover the numerical scheme allows the integration using much longer time steps than any explicit integrator such as the popular Verlet method. If polymers collide the point of impact can be determined to arbitrary precision by simple nested intervals. Once the collision point is known the impulsive contribution can be computed analytically. We illustrate our approach by means of a suitable numerical example
Real-time observation of non-equilibrium liquid condensate confined at tensile crack tips in oxide glasses
Since crack propagation in oxide materials at low crack velocities is partly
determined by chemical corrosion, proper knowledge of the crack tip chemistry
is crucial for understanding fracture in these materials. Such knowledge can be
obtained only from in situ studies because the processes that occur in the
highly confined environment of the crack tip are very different from those that
take place at free surfaces, or that can be traced post mortem. We report the
occurrence of hydrous liquid condensate between the two fracture surfaces in
the vicinity of the tip of tensile cracks in silica. Observations are performed
in real-time by means of atomic force microscopy (AFM) at continuously
controlled crack velocities in the regime of stress corrosion. Condensate
formation and changes in extent and shape are demonstrated for a wide range of
macroscopic humidity at different crack speeds. Its liquid character is
confirmed by the study of AFM phase-contrast data. It is believed that this
evidence of a nanoscale liquid hydrous phase at the crack tip will enable novel
insights in the chemistry of failure of oxide materials.Comment: 13 pages, 4 figures, to be published on J. Am. Cer. So
Shoulder arthroscopy positioning: lateral decubitus versus beach chair.
Since the introduction of the beach chair position for shoulder arthroscopy, orthopaedic surgeons have debated whether the beach chair or lateral decubitus is superior. Most surgeons use the same patient position to perform all of their arthroscopic shoulder procedures, regardless of the pathology. Each position has its advantages and disadvantages. The evidence regarding the efficiency, efficacy, and risks of the lateral decubitus and the beach chair positions for shoulder arthroscopy does not show one position to be superior. This review presents a comparison of these positions with regard to setup, surgical visualization, access, and patient risk
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