A Toupin liquid as an essential ingredient for a smart damper

Toupin's early theory for an elastic dielectric is called upon to describe main events in an active damper.     

Absence of long-range magnetic order in the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite

This paper presents the results of a high-resolution neutron diffraction and magnetometry investigation on the optimally doped (x = 0.3) La(1.4)Sr(0.8)Ca(0.8)Mn(2)O(7) bilayered manganite. In particular, two samples with different oxygen contents have been studied to put in prominence the role of the Mn average valence states at fixed cation concentration. The results show, for the first time, the absence of long-range magnetic order in this optimally doped manganite when the A-site of the structure is doped with equal proportions of isovalent Ca and Sr. This holds for both samples, which present different lattice effects with T, thus suggesting the primary role of cation disorder as the source of the lack of long-range order. The presence, for both samples, of defined insulating- to metallic-like transitions suggests that the transport properties are not linked to the evolution of long-range order and that two-dimensional spin ordering in the layers of the perovskite blocks may be sufficient to "assist" the hole hopping. A possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions.     

Correlation of the Physicochemical and Structural Properties of pDNA/Cationic Liposome Complexes with Their in Vitro Transfection

In this study, we characterized the conventional physicochemical properties of the complexes formed by plasmid DNA (pDNA) and cationic liposomes (CL) composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) (50/25/25% molar ratio). We found that these properties are nearly unaffected at the studied ranges when the molar charge ratio (R(±)) between the positive charge from the CL and negative charge from pDNA is not close to the isoneutrality region (R(±) = 1). However, the results from in vitro transfection of HeLa cells showed important differences when R(±) is varied, indicating that the relationships between the physicochemical and biological characteristics were not completely elucidated. To obtain information regarding possible liposome structural modifications, small-angle X-ray scattering (SAXS) experiments were performed as a function of R(±) to obtain correlations between structural, physicochemical, and transfection properties. The SAXS results revealed that pDNA/CL complexes can be described as being composed of single bilayers, double bilayers, and multiple bilayers, depending on the R(±) value. Interestingly, for R(±) = 9, 6, and 3, the system is composed of single and double bilayers, and the fraction of the latter increases with the amount of DNA (or a decreasing R(±)) in the system. This information is used to explain the transfection differences observed at an R(±) = 9 as compared to R(±) = 3 and 6. Close to the isoneutrality region (R(±) = 1.8), there was an excess of pDNA, which induced the formation of a fraction of aggregates with multiple bilayers. These aggregates likely provide additional resistance against the release of pDNA during the transfection phenomenon, reflected as a decrease in the transfection level. The obtained results permitted proper correlation of the physicochemical and structural properties of pDNA/CL complexes with the in vitro transfection of HeLa cells by these complexes, contributing to a better understanding of the gene delivery process.     

Defect structures and electronic properties in cubic stabilized zirconia

EPR and optical absorption measurements have been performed to detect the defects activated by X-rays in single crystals of zinconium dioxide, stabilized in the cubic phase by the addition of Y₂O₃ in two different concentrations (12 and 24 mol%). Production yield and thermal stability confirm the attribution of the 375 nm optical absorption band to the defect responsible for the EPR T-signal. Deviations from a random distribution of the stoichiometric oxygen vacancies are evidenced. These results agree with the existence of ordering processes in the vacancy system, as predicted by recent structural models.     

Doping effects in single-layered La0.5Sr1.5MnO4 manganite

In this paper we report the results of the synthesis and structural, transport, and magnetic characterization of pure La(0.5)Sr(1.5)MnO(4) and B-site lightly doped samples, i.e. La(0.5)Sr(1.5)Mn(0.95)B(0.05)O(4), where B = Ru, Co, and Ni. The choice was made in order to probe the charge ordering/orbital ordering ground state of the monolayered La(0.5)Sr(1.5)MnO(4) manganite as a consequence of the cation doping. It is shown that even a light doping is successful in suppressing the charge and orbital order found in pure La(0.5)Sr(1.5)MnO(4). No long-range magnetic order has been detected in any of the doped samples but the setup of a spin-glass state with a common freezing temperature ( approximately 22 K). Structural parameters show an anisotropy in the lattice constant variation, with the tetragonal distortion increasing as the cell volume reduces, which may suggest a variation in the orbital character of the e(g) electrons along with the overall cation size.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Role of doping and CuO segregation in improving the giant permittivity of CaCu3Ti4O12

The dopant role on the electric and dielectric properties of the perovskite-type CaCu₃Ti₄O₁₂ (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1-2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90<ε_r<180. Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07 eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76 eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.     

Sonographic evaluation of subacromial space

GOAL OF THE STUDY: The purpose of this study is to compare the accuracy of sonographic to radiographic measurements of subacromial space, and verify its variations in relation to acromial morphology, age, sex and rotator cuff pathologies. MATERIALS AND METHODS: As a result, we have compared a radiographic examination to sonographic examination, each measuring the subacromial space in 200 random shoulders, with a personal method. The sonographic examination was performed by using a HDI 5000 ultrasound scanner Sono-CT with 7.5 MHz linear array transducer. No stand-off pad was utilized. RESULTS: The statistical analysis of the data derived from the two measurements was not sufficient to conclude that the two techniques are different (p>0.8). They also correspond with the radiographic morphology of the acromion. The size of subacromial space was related to the acromial morphology, female gender, and rotator cuff pathology, however, it was not related to age. DISCUSSION AND CONCLUSIONS: Our results clearly show that sonographic measurements are very close to those obtained by X-ray (p>0.8). The Bland-Altman analysis showed that for all groups, the were small enough to give us confidence that the sonographic technique may be used in place of the radiographic one for clinical purposes. One-way ANOVA showed that sonographic measurements were statistically different among the four groups (p<0.05). The sonography demonstrated precision, accuracy and carefulness in the measurement of the subacromial space.