631 research outputs found
Synthesis and characterization of multiferroic BiMnO
We report on the high pressure synthesis of BiMnO, a manganite
displaying a "quadruple perovskite" structure. Structural characterization of
single crystal samples shows a distorted and asymmetrical coordination around
the Bi atom, due to presence of the lone pair, resulting in
non-centrosymmetric space group Im, leading to a permanent electrical dipole
moment and ferroelectric properties. On the other hand, magnetic
characterization reveals antiferromagnetic transitions, in agreement with the
isostructural compounds, thus evidencing two intrinsic properties that make
BiMnO a promising multiferroic material.Comment: 4 pages, 3 figure
Internal-strain mediated coupling between polar Bi and magnetic Mn ions in the defect-free quadruple-perovskite BiMnMnO
By means of neutron powder diffraction, we investigated the effect of the
polar Bi ion on the magnetic ordering of the Mn ions in
BiMnMnO, the counterpart with \textit{quadruple} perovskite
structure of the \textit{simple} perovskite BiMnO. The data are consistent
with a \textit{noncentrosymmetric} spacegroup which contrasts the
\textit{centrosymmetric} one previously reported for the isovalent and
isomorphic compound LaMnMnO, which gives evidence of a
Bi-induced polarization of the lattice. At low temperature, the two
Mn sublattices of the and sites order antiferromagnetically
(AFM) in an independent manner at 25 and 55 K, similarly to the case of
LaMnMnO. However, both magnetic structures of
BiMnMnO radically differ from those of LaMnMnO.
In BiMnMnO the moments of the sites form
an anti-body AFM structure, whilst the moments \textbf{M} of the
sites result from a large and \textit{uniform} modulation along the b-axis of the moments \textbf{M} in the
-plane. The modulation is strikingly correlated with the displacements of
the Mn ions induced by the Bi ions. Our analysis unveils a strong
magnetoelastic coupling between the internal strain created by the Bi
ions and the moment of the Mn ions in the sites. This is ascribed to
the high symmetry of the oxygen sites and to the absence of oxygen defects, two
characteristics of quadruple perovskites not found in simple ones, which
prevent the release of the Bi-induced strain through distortions or
disorder. This demonstrates the possibility of a large magnetoelectric coupling
in proper ferroelectrics and suggests a novel concept of internal strain
engineering for multiferroics design.Comment: 9 pages, 7 figures, 5 table
Organic Inhibitors to Prevent Chloride-Induced Corrosion in Concrete: Atomistic Simulations of Triethylenetetramine-Based Inhibitor Film
Inhibitors are largely used to prevent chloride-induced corrosion in reinforced concrete structures thanks to both a barrier effect on chloride penetration and a competition with the adsorption of the inhibitor. The interaction mechanisms between passive film on carbon steel, the inhibitor molecule, and chlorides still require deeper understanding. Theoretical studies based on molecular mechanics (MM) and molecular dynamics (MD) methods can be useful to better understand the passive film formation and its interaction with chlorides. In this work, the interaction between a triethylenetetramine (TETA) inhibitor film on γ-FeOOH surface and chlorides is studied using MD methods. After MM optimization in the initial adsorption stage, some chlorides are close to protective TETA film. After MD run at room temperature effectively, chlorides remain close to the protective film. In order to have an effective barrier on chloride attack, the metal oxide must remain wholly covered by the protective film. The TETA film well covers the lepidocrocite surface but cannot kinetically efficiently prevent the chloride-induced corrosion compared to other organic films exposing COO− groups because it does not exert any repulsion to chlorides
Electron localization and possible phase separation in the absence of a charge density wave in single-phase 1T-VS
We report on a systematic study of the structural, magnetic and transport
properties of high-purity 1T-VS powder samples prepared under high
pressure. The results differ notably from those previously obtained by
de-intercalating Li from LiVS. First, no Charge Density Wave (CDW) is found
by transmission electron microscopy down to 94 K. Though, \textit{ab initio}
phonon calculations unveil a latent CDW instability driven by an acoustic
phonon softening at the wave vector (0.21,0.21,0)
previously reported in de-intercalated samples. A further indication of latent
lattice instability is given by an anomalous expansion of the V-S bond distance
at low temperature. Second, infrared optical absorption and electrical
resistivity measurements give evidence of non metallic properties, consistent
with the observation of no CDW phase. On the other hand, magnetic
susceptibility and NMR data suggest the coexistence of localized moments with
metallic carriers, in agreement with \textit{ab initio} band structure
calculations. This discrepancy is reconciled by a picture of electron
localization induced by disorder or electronic correlations leading to a phase
separation of metallic and non-metallic domains in the nm scale. We conclude
that 1T-VS is at the verge of a CDW transition and suggest that residual
electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase
with metallic properties.Comment: 22 pages, 10 Figures. Full resolution pictures available at
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.23512
Direct-current stimulation of posterior tibial nerve modulates the Soleus H-reflex amplitude
Introduction: Several studies demonstrated that transcranial direct current stimulation (tDCs) is a promising non-invasive tool able to modulate the excitability of several CNS structures. Its effect is usually facilitatory when using anodal polarity and inhibitory for the cathodal one. In most studies, DC stimulation was applied on cortical or spinal structures, while little is known about its effect on peripheral nerves fibres. This research aims at highlighting such effect. Methods: In twenty subjects, electrical stimulation of the posterior tibial nerve (1 ms current pulses, 1 shock every 9 s) was used to elicit the H-re\ufb02ex in the Soleus muscle. Once the H-re\ufb02ex amplitude was stable for at least 15 min, DCs (either cathodal or anodal) was applied proximally to the same nerve for 10 min, looking for changes in re\ufb02ex amplitude. Then, the H-re\ufb02ex was measured for 30 further minutes, looking for after-effects. Results: Cathodal DCs induced a significant increase of the H-re\ufb02ex amplitude (about +35%) with respect to the control value. In this configuration the after-effect lasted about 25 min. Anodal DCs induced instead a significant decrease (about -25%) of the re\ufb02ex amplitude. A significant after-effect was observed for just about 5 min. Discussion: This study shows that DCs applied to a peripheral nerve is able to elicit neuromodulation. Its polarity dependence suggests a local change in the excitability of nerve fibres rather than a central modulation of the spinal re\ufb02ex circuit. Moreover it is worth to note that the polarity dependence was opposite to what found for tDCS
Utilizzo di nitrati come inibitori di corrosione per le armature nel calcestruzzo
Corrosion inhibitors have been long considered as an effective preventative technique to slow down the onset
and/or propagation of corrosion phenomena in reinforced concrete. Several substances have been evaluated
as possible candidates, and great interest has been dedicated to nitrite ion. When investigating how these
substances slow down corrosion related processes – chlorides diffusion, critical chloride threshold, CO2
penetration and corrosion propagation –interactions between inhibitor and concrete are also vital.
Recently, nitrate based compounds have been proposed as corrosion inhibitors, as they present lower cost
than nitrites and are already used in concrete as set accelerators. Some studies have shown that nitrates
inhibiting mechanism is similar to that of nitrites. This work proposes the evaluation of a nitrate based
substance as possible corrosion inhibitor in concrete, and compares its performance with a nitrite based
inhibitor
Implants outcome inserted in different sites
Oral rehabilitation by means dental implants has high standards of success. Recently, a new type of two-pieces spiral implants has been introduced in the market. Since few reports focus of the efficacy of this medical device as a reliable tool for oral rehabilitation, here a retrospective study is reported. In the period June-December 2017 one hundred and two spiral fixtures were inserted, half in females and 51 in males. The median age was 56 \ub1 8 (min-max 36-73 years). Forty-eight implants were inserted in upper jawbone and 54 in mandible. Two implants were lost and thus survival rate (SVR) is 99.9%. Then peri-implant bone resorption was used to investigate the clinical success (success rate, SCR) over time. No implants have a crestal bone resorption greater than 1.5 mm in the first year follow up. No studied variable has an effect on clinical outcome. In conclusion the studied implants have high SCR and SVR so that they are good tools for oral rehabilitation
Evaluation of quality of drinking water from Baghdad, Iraq
This is a joint work between the Italian Red Cross and the Environmental Laboratories, Baghdad. The drinking water (DW) samples from 16 residential districts in Baghdad were chemically evaluated with reference to the raw water samples and water directly taken from the purification plants. In addition to the routinely measured parameters, 17 metals and 11 trihalomathane (THM) were measured. Generally, the samples of water analysed can be considered of good quality. The relatively high sulphate and aluminium contents results from the use of aluminium sulphate as flocculent. The ammonia and Nitrite concentrations were lower than the detectable limit, because ammonia is converted into chloramines and nitrite is converted into Nitrate during chlorination. This indicates no sewage contamination of the drinking water. The high chloride contents can be referred to the use of partially degraded hypo for the disinfection. The presence of THM's in the samples analysed is indicative of good disinfection process. The presence of these compounds is preferred better than bacterial contamination. The relatively high levels of zinc and iron have no impact on the quality of DW. Iron, however, was efficiently removed during the treatment, together with Manganese. Reference was done to the EU specification of drinking water regarding total hardness, chloride contents, sulphate, iron and THM's. As for the iron content, the original pH of the river water (7.5 and 8.0) ensures that Iron should not be present in soluble form at a detectable level. Corrosion of the pipes could be one of the reasons for the presence of iron.
Key Words: Drinking water quality, heavy metals, sulphate, Aluminium, Trihalomethans, hardness
Direct current stimulation modulates the excitability of the sensory and motor fibres in the human posterior tibial nerve, with a long-lasting effect on the H-reflex
Several studies demonstrated that transcutaneous direct current stimulation (DCS) may modulate central nervous system excitability. However, much less is known about how DC affects peripheral nerve fibres. We investigated the action of DCS on motor and sensory fibres of the human posterior tibial nerve, with supplementary analysis in acute experiments on rats. In forty human subjects, electric pulses at the popliteal fossa were used to elicit either M-waves or H-reflexes in the Soleus, before (15 min), during (10 min) and after (30 min) DCS. Cathodal or anodal current (2 mA) was applied to the same nerve. Cathodal DCS significantly increased the H-reflex amplitude; the post-polarization effect lasted up to ~ 25 min after the termination of DCS. Anodal DCS instead significantly decreased the reflex amplitude for up to ~ 5 min after DCS end. DCS effects on M-wave showed the same polarity dependence but with considerably shorter after-effects, which never exceeded 5 min. DCS changed the excitability of both motor and sensory fibres. These effects and especially the long-lasting modulation of the H-reflex suggest a possible rehabilitative application of DCS that could be applied either to compensate an altered peripheral excitability or to modulate the afferent transmission to spinal and supraspinal structures. In animal experiments, DCS was applied, under anaesthesia, to either the exposed peroneus nerve or its Dorsal Root, and its effects closely resembled those found in human subjects. They validate therefore the use of the animal models for future investigations on the DCS mechanisms
Influence of Hydrogen and Low Temperature on Pipeline Steels Mechanical Behaviour
Abstract In the presence of H2S, metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. Gas transporting pipes in low temperature environment, during the shutdown and the subsequent re-starting operations, are exposed to very low temperatures (T=-40 °C). In the presence of high H2S content in the gas, the risk of brittle failure can be increased due to the effect of hydrogen on steel toughness. In this paper the influence of hydrogen and low temperature on mechanical properties of two pipeline materials, F22 low alloy and X65 micro-alloyed steels, is studied. Steels have been hydrogen charged by means of an electrochemical method: diffusible hydrogen content of steels is in the range 0.6 to 2 ppm. Charpy and J-R curves tests were carried out in the range from room temperature to T=-120 °C. Hydrogen affects mechanical properties of the tested materials, mainly reducing fracture toughness in J integral tests, while little influence has been observed in CV tests. Fracture surface examination confirms the results of mechanical testing
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