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Aim: The aim of this study was to verify the influence of caffeine (CAF) on time to exhaustion in a maximal incremental exercise test and cardiac autonomic indexes recovery in chronic obstructive pulmonary disease (COPD) patients. Methods: In a randomized, double-blinded, placebo-controlled and crossover experimental design, eleven patients diagnosed with COPD performed an incremental test after ingesting CAF (5 mg kg−1) or placebo (PLA) (cellulose). CAF or PLA was administered 60 min before the test. Peripheral oxygen saturation was analyzed throughout the tests. Heart rate recovery (HRR) and variability (HRV) were analyzed after exhaustion in both tests. Additionally, six patients completed a spirometry after ingesting a capsule of caffeine. Results: The time to exhaustion in the incremental test with CAF (355.8 ± 171.1 s) was 2.1% longer than in the PLA test (348.5 ± 209.1 s), but there was no statistical difference (p = 0.70). Similarly, no statistical differences were observed in HRR and HRV between PLA and CAF (p > 0.05 for all analyses). The peripheral oxygen saturation values were lower at exhaustion but without a statistical difference (CAF = 92.3 ± 4.4% vs. PLA = 91.5 ± 2.7%; p > 0.05). After spirometry, the effect of CAF on FEV1 (Before CAF = 1.43 ± 0.75 L vs. After CAF = 1.47 ± 0.70 L; p = 0.17) was not demonstrated. Conclusion: Caffeine does not change incremental test performance and autonomic recovery response in patients with COPD. These results suggest caffeine would not have an ergogenic effect in patients with COPD. [ABSTRACT FROM AUTHOR]

In this article, we have investigated the structural, Mossbauer, thermal and dielectric properties of the ZnFeCoO4 spinel oxide elaborated using the sol–gel process. We have used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the microstructural properties of our sample. The XRD pattern shows the formation of the ZnFeCoO4 compound as the main phase, matched with the cubic spinel structure, as well as a secondary phase of ZnO was also identified. The SEM micrograph shows the spherical shape of grains with porosity. The Raman spectra reveal five Raman active optical modes (A1g + Eg + 3T2g), confirming the spinel structure of the prepared sample. The electrical conductivity measurements were analyzed using Jonscher universal power law σ ω = σ dc + A ω p . The temperature dependence of the exponent p suggests that the non-overlapping small polaron tunneling model (NSPT) is the appropriate conduction mechanism within the synthesized sample. The variation of dielectric permittivity is explained in terms of interfacial polarization based on the Maxwell–Wagner theory. The plots of the imaginary parts of the modulus (M″) reveals two specific relaxation frequency shifted to higher frequencies with increasing temperature. The activation energies deduced from the dc conductivity and electrical modulus are comparable implying that the relaxation and conduction processes are caused by the same type of charge carriers. Nyquist plots (Z″ vs. Z′) were well adjusted using an equivalent circuit that includes both grain and grain boundary response, hence, the equivalent circuit configuration is a type of [(Rg//CPEg) + (Rgb//CPEgb)]. [ABSTRACT FROM AUTHOR]

Propyl sulfonic SBA-15 catalysts are of great interest in several fields of chemistry and have exhibited high activity towards numerous reactions. Nonetheless, the incorporation of these functional groups on SBA-15 silica poses several challenges. Grafting techniques may conduct to a non-uniform dispersion of the functional groups on the surface. Co-condensation of the functional precursor during the synthesis of the silica overcomes this drawback, but requires longer syntheses and it has the disadvantage that removal of surfactant cannot be done by calcination because of the thermal stability of the functional groups present on the surface. Thus, the detemplation is limited in this case to extraction by standard procedures which generally involve large amounts of solvent per gram of catalyst, long contact time and limited yield of the template removal. The aims of this work were, on the one hand, to study the reduction of the ripening time for catalysts prepared by co-condensation with sulfonic groups and, on the other hand, to develop a standard procedure which allows achieving a high yield of detemplation and optimizes the amount of solvent needed and the time required, as well as employ a commercially available solvent. Different characterization techniques allowed to conclude that the obtained materials exhibited high surface area and a good degree of mesoscopic order, comparable with materials obtained by traditional procedures. Also, a high degree of template removal was achieved and the sulfonic groups were preserved in functionalized materials. These results are relevant for a further scale-up of the catalysts production. [ABSTRACT FROM AUTHOR]

The L i Mg 2 Fe 3 O 7 compounds were prepared by via the citrate process and sintered at two different temperatures to study their effect on structural, morphological, optical, and electric properties. The X-ray diffraction analysis revealed that both samples crystallized in a cubic spinel structure belonging to space group F d 3 ¯ m . Increasing the sintering temperature led to an increase in the grain size as characterized by SEM. The UV–visible spectroscopy revealed that the band gap is 2.5 eV and 2.35 eV for M g 700 and M g 1100 , respectively, which confirm that these compounds are potential candidates for optoelectronics. The electrical resistance was found to decrease with the increase in the sintering temperature, consequently leading to a rise in conductivity. [ABSTRACT FROM AUTHOR]

In the present research work, the sol–gel auto-combustion preparation method using two different fuels agents (citric acid and glycine) was used to synthesize CoFe2O4 nanoparticles. The structural and morphological studies were performed to confirm the ability to obtain a pure cubic spinel phase with a particle size < 100 nm. The particle size effects on structural, Raman and magnetic properties of the CFO was studied to confirm that the glycine fuel decreased the particle size and the saturation magnetization. The CoFe2O4 nanoparticles were found to exhibit a considerable value of maximum energy product (BH)max, which makes them good candidate for permanent magnet applications. Notably, the cytotoxic activity of both prepared compounds against two different human breast cancer cells (T47-D and MDA-MB-231) and one prostate cancer cell (PC3) were evaluated. Both C1 and C2 compounds are quite cytotoxic against the human breast and prostate cancer cells and the C2 with lower particle size was found to have the higher cytotoxic potency (minimum viability values) with 49%, 39% and 19% in MDA-MB-231, PC3 and T47-D cancer cells, respectively. The cytotoxicity against normal human cells was found to be lower than 3% even for high C2 particle concentrations, reflecting the human-safe-and-friendly nature of the CoFe2O4. [ABSTRACT FROM AUTHOR]

Doped LaFeO3 materials are of high utility for energy storage devices and gas sensors. This work explores the effect of particles size and the preparation method on the physico-chemical properties of the (La0.8Ca0.2)0.6Bi0.4FeO3 compound. Accordingly, it was prepared by the Sol–Gel (LCBFO-SG) and the solid-state (LCBFO-SS) reaction methods. According to the Rietveld method, the adjusted XRD data confirm the distorted orthorhombic phase for both compounds. For both samples, the giant dielectric constant and the low loss tangent showed two relaxation processes at high- (grains boundary) and low-temperature regions (grains). The Havriliak-Negami ana Bergman formalism, used to adjust the imaginary part of dielectric Modulus, confirmed a non-Debye dielectric process. For both compounds, the conduction mechanism is ascribed to the non-Overlapping Small Polaron hopping between iron states. Importantly, Gas-sensing tests revealed that the LCBFO-SG nanoparticles exhibited higher response values and fast response/recovery times to ethanol, acetone, and H2S gases which is correlated with its lowest particles size. These results confirm that the LCBFO-SG could be an effective candidate for multi-gas sensors. [ABSTRACT FROM AUTHOR]

The purpose of this study was to verify the influence of physical activity level on the length of hospital stay in older men recovered from COVID-19. In total, 126 older men diagnosed with COVID-19 were admitted to the hospital between September and December 2020. Among them, 70 survived, of which 39 older men were included in the study. Within 30 days after discharge, patients answered the International Physical Activity Questionnaire to measure their physical activity level through phone contact, with questions corresponding to the week before symptom onset. Clinical and laboratorial data from admission, days between onset of symptoms and admission, length of stay, computed tomography abnormalities, and the need for the intensive care unit were collected. The groups (active × sedentary) were compared using the Student t test or Mann–Whitney test for quantitative data and chi-square test was used for categorical data. There is no difference between the groups in characteristics of admission (p > 0.05), except by potassium level. Active older men had a shorter length of stay (6.50 ± 3.46 vs 11.48 ± 7.63 days; p = 0.03), disease duration (15.71 ± 4.84 vs 21.09 ± 7.69 days; p = 0.02), and lower frequency of lung damage when compared to their sedentary counterparts. In conclusion, being physically active prior to infection can attenuate length of hospital stay in older men with COVID-19. [ABSTRACT FROM AUTHOR]

The two-dimensional Ising model with disorder in the spin-spin interactions is studied using the zeros of the energy probability distribution (EPD) to obtain the phase diagram of the quenched three-dimensional ( L 3 ) ± J Ising model. Starting with a complete ferromagnetic (anti-ferromagnetic) system, we introduce at random a number of p × L 3 anti-ferromagnetic (ferromagnetic) bonds in the system. The phase diagram, temperature against the bond concentration (p), is obtained. The goal of this preliminary study is to show how it is possible to determine the phase diagram of such a complex model with no need to introduce an order parameter. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the structural, electrical, and dielectric properties of Ni0.1Co0.5Cu0.4Fe2-xCrxO4 (x = 0 and 0.3) ferrites. Samples have been prepared by employing the sol–gel method. The X-ray diffraction data along with Rietveld refinement were used to assess the phase purity and the structural parameters of samples. The morphology and the grain size of the prepared ferrite nanocrystals were observed with scanning electron microscopy. At room temperature, the Raman spectra displayed active phonon modes. FTIR spectra revealed two principal absorption bands due to the stretching vibration of metal oxygen in tetrahedral and octahedral sites. With increasing of Cr3+ concentration, both Raman and FTIR spectra showed that all modes shifted to higher wavenumbers. The dielectric properties were investigated using impedance complex spectroscopy in the frequency region (100‒106 Hz) at different temperatures. The ac-conductivity for both studied compounds was well analyzed using the augmented Jonscher equation. The plots of both imaginary part of permittivity (ε″) and dielectric loss (tanδ) vs. frequency, exhibit a dielectric dispersion in our compounds at low frequencies. This is described according to the Maxwell–Wagner model in agreement with Koop's theory. The modulus curve was used to interpret the relaxation behaviors of charge carriers. The Nyquist plots of impedance for both samples have been modeled using the same equivalent circuit which is formed by a three-element R-CPE connected in series. [ABSTRACT FROM AUTHOR]

In this paper, we present a Monte Carlo study of the critical behavior of the easy axis anisotropic Heisenberg spin model in two dimensions. Based on the partial knowledge of the zeros of the energy probability distribution, we determine with good precision the phase diagram of the model obtaining the critical temperature and exponents for several values of the anisotropy. Our results indicate that the model is in the Ising universality class for any anisotropy. [ABSTRACT FROM AUTHOR]

We report an investigation of the structural, morphological, the ac-dc electrical, magnetic, and Mössbauer spectroscopy properties of 20MnFe2O4-80SiO2 nanocomposite prepared using a one-step and facile auto-combustion approach. XRD pattern shows the formation of MnFe2O4 nanocrystallite without any crystallization of the SiO2 phase. However, the presence of a secondary phase of the nanosized α-Fe2O3 particles was also detected. The morphological analysis showed aggregation of polygonal magnetic nano-crystallites dispersed non-uniformly in a silica matrix. The dc electrical measurements performed on a wide range of temperatures from 120 to 400 K showed the semiconducting nature of the nanocomposite. The temperature dependence of dc conductivity could be perfectly fitted to the nearest neighborhood hopping model with activation energy, ΔENNH, of 0.45 eV. The Nyquist plots demonstrated a nonmonotonous thermally activated trend and non-Debye relaxation behavior. An equivalent circuit was successfully fitted to the complex impedance spectra. The variation of both grain and grain boundary conductivities as a function of temperature exhibited three distinct regions, semiconducting-metallic-semiconducting with different activation energies over the measured temperature window. The provided description of such behavior is further advocated by the ac conductivity and dielectric modulus studies. VSM measurements revealed that the nanocomposite magnetic behavior deviates from the ideal non-interacting superparamagnetic picture, due to the presence of α-Fe2O3 nanocrystalline impurities and relatively intensive exchange interactions between ions. Mössbauer spectra showed the presence of Fe3+ ions with sixfold environment and also confirmed the existence of a sextet related to α-Fe2O3 with a quantity of about 20% out of magnetic components. Fe3+ superparamagnetic doublets were also found within the fitting procedure. [ABSTRACT FROM AUTHOR]

The present paper explores of the lanthanum and calcium insertion effect on the physico-chemical properties of the Bi0.8(La0.8Ca0.2)0.2FeO3 (LCBFO-8) Sol–Gel made multiferroic compound. The LCBFO-8 compound crystallized in a rhombohedral distorted structure with the R3c space group. The Morphological investigation confirmed the nanosize criteria of the examined nanoparticles with an average particle size less than 50 nm. Notably, the studied compound shows a colossal dielectric constant, low loss tangent tg(delta) values, an enhanced magnetization, and a reduction of the Curie transition temperature to 395 K, which confirms well the high utility of such compound for energy storage applications. At low and high temperatures, two dielectric relaxations have been detected in the frequency dependence curves of the dielectric constant and the Modulus imaginary part plots at low and high-temperature ranges. The symmetric and asymmetric dielectric parameters α and β have been collected from the adjustment of the M″ based on the Havriliak–Negami (H–N) formalism. According to their values, it can be concluded that the high-temperature relaxation is a Cole–Cole-type dielectric relaxation, while the Cole–Davidson model fits the high temperature well. [ABSTRACT FROM AUTHOR]

Pure and 15% bismuth-doped cobalt spinel ferrites [CoFe2O4 (CFO) and Co0.85Bi0.15Fe2O4 (CBFO)] were synthesized by the auto-combustion method using glycine as the fuel agent. Both structural and morphological studies confirmed the nanosize criteria for both compounds with an increase in particle size when introducing bismuth ions. The insertion of non-magnetic ions in the A-site of CFO compound induced a decrease in the saturation magnetization due to the increase of the antiferromagnetic interactions. The biocompatibility of CFO and CBFO nanoparticles with two different human breast cancer cells (T47-D and MDA-MB-231) and one prostate cancer cell (PC3) was evaluated. The CBFO compound induced a higher cancer cell mortality with IC50 values of 61.12, 66.41 and 134.38 µM, for MDA-MB-231, T47-D and PC3 cancer cells, respectively. The cytotoxicity against normal human cells was found to be lower than 2% even for high CBFO particle concentrations. Accordingly, both prepared compounds could be considered as potential therapeutic agents against cancer cells. [ABSTRACT FROM AUTHOR]

The use of partition function zeros in the study of phase transitions is growing in the last decade mainly due to improved numerical methods as well as novel formulations and analysis. In this paper, the impact of different parameters choice for the energy probability distribution (EPD) zeros that were recently introduced by Costa et al. is explored in search for optimal values. Our results indicate that the EPD method is very robust against parameter variations and only small deviations on estimated critical temperatures are found even for large variation of parameters, allowing one to obtain accurate results with low computational cost. A proposal to circumvent potential convergence issues of the original algorithm is presented and validated for the case where it occurs. [ABSTRACT FROM AUTHOR]

Background and aim: Shunt dysfunction is a common event, especially in children who have this intervention performed early in life. The consequences of chronic shunt overdrainage can be multiple since the cerebral hydrodynamics is altered. A thrombotic event with consequent symptoms of intracranial hypertension is discussed in this article. Material and methods: We performed a detailed review of cerebral hydrodynamics and intracranial pressure compensation mechanisms and how this can alter cerebral venous circulation. Next, we report the case of a 4-year-old child with such a clinical presentation that was conducted by our team. Results: A child with a history of hydrocephalus treated with a ventriculo-peritoneal (VP) shunt in his early childhood presented with symptoms of intracranial hypertension, initial computed tomography (CT) demonstrating reduced-sized ventricles. Complementary investigation showed bilateral papilledema, cranial suture closure, changes compatible with Chiari type I, and venous sinus thrombosis (transverse and sigmoid, bilaterally). The case was managed conservatively with full anticoagulation with enoxaparin. Four months after the onset of symptoms, there was an improvement in the clinical and imaging status. Conclusion: A condition of severe headache in a patient with an apparently functioning shunt and small ventricles on initial CT should open up a range of diagnostic possibilities, with pseudotumor cerebri syndrome and cerebral venous sinus thrombosis being suggested. The therapeutic approach in these cases must be individualized. [ABSTRACT FROM AUTHOR]

In this study, La0.67Ca0.2Ba0.13Fe1−xCrxO3 (x = 0 and 0.03) powders were prepared by auto-combustion method. The examination of the purity and crystalline structure of the samples by X-ray diffraction showed a cubic structure formed with the P m 3 ¯ m space group. Scanning electron microscopy was used to study the morphology and grains size, indicating an agglomeration of nanometric particles. Impedance spectroscopy in the temperature range from 200 to 360 K was used in order to understand the evolution of the electrical behavior of the substituted perovskites. The real and imaginary parts of the impedance were adjusted with two different equivalent circuits. The activation energies extracted from the imaginary part of the impedance, and the electrical conductivity was very closed indicating a transformation of the electrical behavior. This was confirmed by a decrease in the resistance after substitution of Fe cations by Cr ones. AC conductivity studies showed a Jonscher's behavior and a change of conduction process from a succession of NSPT and CBH model to the existence of only CBH one after the substitution. [ABSTRACT FROM AUTHOR]

In the present investigation, La0.75Ba0.10Sr0.15FeO2.875-δ oxygen-deficient ferrites with δ = 0.00, 0.125 and 0.25 were synthesized by sol–gel method. The physical characterization has been carried out by X-ray diffraction, scanning electron microscope SEM, Raman spectroscopy, and complex impedance. All samples are formed in orthorhombic crystal symmetry with Pnma space group. Synthesized compounds have nanocrystallite size of 32–46 nm. Raman spectrum shows the oxygen vacancy effect on the tilt and stretching phonon modes. Electric properties were investigated in the framework of impedance and electric conductivity. The complex impedance was measured over a wide range of temperatures (300–380 K) and frequencies (40 Hz–1 MHz). The electrical measurements indicate semiconductor behavior for the three compositions and emphasize the evidence of contribution of grain boundaries in the transport properties. The ac conductivity curves obey the Jonsher universal power law and are assigned to hopping conduction mechanism. It is found that the values of activation energy, estimated from the conductivity analysis, are in the same order with those deduced from relaxation process. Such result proves that both processes, conduction and relaxation, are related to the same defect. [ABSTRACT FROM AUTHOR]

A methodical study on structural, electrical and dielectric properties of NiFeCoO4 nanoparticles, synthesized via sol-gel technique has been reported in this article. X-ray diffractogram confirmed phase purity of the synthesized sample. Raman spectra show the five predicted Raman bands that appear around 600–720, 250–360, 500–590, 450–520 and 180–220 cm−1 corresponding to A1g, Eg, T2g (3), T2g (2) and T2g (1), respectively. From the dielectric measurements, we have determined the different dielectric parameters such as the conductivity σac, complex permittivity ε*, complex impedance Z*, and the tangent loss (tanδ). The electrical properties strongly depend on temperature and frequency. The relaxation activation energy deduced from the Z" vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the same type of charge carriers are attributed to the relaxation process and the conduction mechanism. The complex impedance plots have revealed the presence of only one semicircular arc corresponding to grains and grain boundaries contributions at all the temperatures and an equivalent electric circuit was proposed as a model of the sample. Highlights: The Ni0.5Zn0.5FeCoO4 spinel ferrite is synthesized by a sol-gel technique. The temperature and frequency dependence of dielectric constants have been investigated. The electrical properties are found to be strongly dependent on temperature and confirmed the presence of one semicircular arc by the Nyquist plots. The analysis of the thermal variation of the imaginary part of the electrical modulus peak has indicated that the observed relaxation process is thermally activated. [ABSTRACT FROM AUTHOR]

The La0.67Ca0.2Ba0.13Fe1−xMnxO3 perovskite compounds with different manganese concentrations (x = 0.0, 0.03, 0.06) were synthesized by the autocombustion method and annealed at 700 °C. The X-ray diffraction (XRD) data indicated that all obtained compounds crystallize in the cubic structure with the Pm 3 ¯ m space group. The increase in the substitution rate has been found to lead to the decrease in the crystallite size value characterized by X-ray diffraction. The dielectric properties of these samples, using a complex impedance spectroscopy technique, were also performed as a function of frequency and temperature. A suitable equivalent electrical circuit was used to assess the contributions of electrode, grains, and grain boundaries in the complex impedance results. Activation energies were determined from different methods. Nyquist plots were consistent with three circuits in series, each one with a capacitance in parallel with a resistance. The conduction mechanism follows the NSPT model for the three samples at T < 280 K, in which the rise in substitution rate increases the binding energy of carriers. Above 280 K, the appropriate model is the Correlated Barrier Hopping (CBH) for x = 0, while the overlapping large polaron tunneling (OLPT) process has been confirmed for both samples x = 0.03 and x = 0.06. Our compounds have high electrical properties, and good thermal and chemical stability. They are susceptible to many technological applications, such as gas sensors, capacitors, filters, resonators, new read heads, and solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Perovskite-type oxides La1-xBixNi0.5Ti0.5O3 (x = 0.0, 0.2) were prepared by the sol–gel method employing the citric acid route and sintered at 820° C. The structural behavior analyzed by X-ray diffraction proved that all the samples have the same crystallographic structure (space group Pnma). The volume of the elemental lattice decreases with the rate of Bismuth substitution. Transmission electron microscopy (TEM) verified the nanosized grains. The FTIR spectra confirmed the formation of the orthorhombic perovskite structure. UV–Visible spectroscopy and photoluminescence were also applied to study the samples. The parameters of real and imaginary part of dielectric function (ε′ and ε″) and dielectric loss tangent (tg(δ)) show a strong frequency dependence. Those dependences explain a dispersive behavior at low frequencies and are outlined on the basis of the Maxwell–Wagner model and Koop theory. The compounds have very high dielectric constant values (ε′ ≈ 103) that are useful in electronic devices. Electric modulus formalism was employed to investigate the relaxation dynamics of charge carriers. Moreover, a non-Debye type of relaxation was verified in our samples. The activation energy is specified from the analysis of the imaginary part of the electric modulus. [ABSTRACT FROM AUTHOR]

The cobaltite spinel MnCo2O4 nanopowder was prepared by the sol–gel method. X-ray diffraction shows the pure compound that crystallized in the cubic structure with the Fd 3 - m space group. The infrared spectrum (IR) revealed two absorption peaks that can be attributed to Mn–O and Co–O vibrations in the octahedral and tetrahedral sites, respectively. The electrical and dielectric studies were characterized by impedance spectroscopy (IS) at different frequencies (40–106Hz) and temperatures (200–440K). As a matter of fact, the DC conductivity exhibits a semiconductor behavior. It is worth mentioning that the conductivity of our investigated cobaltite spinel was found to be σ = 6.10−3 Sm−1 at room temperature. These results allowed this material to be a good candidate for potential application as an anode material (fuel cell). The AC conductivity obeys the Jonscher's law at low temperatures T < 340K and the Drude model at high temperatures T > 340K. Moreover, the dielectric result shows the permittivity (ε '≈ 103) which is due to the contribution of the Maxwell–Wagner polarization. [ABSTRACT FROM AUTHOR]

In this work, we report the structural, electrical, and optical properties of nontoxic and earth-abundant Na2ZnSnS4 (NZTS) material. NZTS powder has been successfully synthesized using an easy and nontoxic pathway: the solid-state reaction technique. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy were used to study the structural properties of the NZTS. The synthesized powder crystallized in the stannite tetragonal structure with lattice parameters a = 6.48 Å and c = 9.12 Å. XRD and Raman characterizations showed the occurrence of the secondary phase Na4SnS4. Optical bandgap measurements were obtained from UV–Visible analysis and showed a high optical bandgap value of 3.32 eV and confirmed the presence of Na4SnS4. TEM micrographs provide a description of the morphology of NZTS. The HRTEM images reflect a preferred orientation along the {112} plane, which is consistent with the X-ray diffraction pattern. EDS analysis confirmed the presence of the four constituent elements of the NZTS within their corresponding composition. NZTS powder indicates a conductivity type n. A study of electrical conductivity was carried out by using the impedance spectroscopy. The frequency and temperature dependence of the complex electrical impedance and AC and DC conductivity were explored. These interesting results make the NZTS particularly attractive for solar cell applications and especially suitable as a window layer. [ABSTRACT FROM AUTHOR]

The aim of this research work was to study the structural and magnetic properties of iron oxide nanoparticles. The as-prepared sample was synthesized by a co-precipitation route and annealed at different temperatures. The annealed samples were investigated using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and Mössbauer spectrometry (MS). The XRD results indicate the formation of three phases which have been identified as magnetite (Fe3O4), maghemite (γ-Fe2O3), and hematite (a-Fe2O3). The crystallite size was very similar for both magnetite and maghemite, and it was higher for hematite. The TEM observations showed that the particle shapes were affected by the annealing temperature (Tan). In addition, the SEM analysis revealed a wide distribution of the particle size. The magnetic measurements enabled the determination of a blocking temperature for both Fe3O4 and γ-Fe2O3 as 210 and 240 K, respectively. The Morin transition temperature was determined in the case of α-Fe2O3 from the magnetization and the MS measurements. The synthesized iron oxide nanoparticles can be good candidates for hyperthermia applications. [ABSTRACT FROM AUTHOR]

The La0.8Ba0.1Ce0.1FeO3 compounds were prepared by the auto-combustion route and annealed at two different temperatures to study their effect on the structural, morphological and dielectric properties of the Barium- and Cerium-substituted LaFeO3 compound. The X-ray diffraction analysis revealed that both compounds crystallized in the orthorhombic structure belonging to the Pnma space group. The rise of the annealing temperature from 700 to 900 °C was found to lead to the increase of the average grain size value as characterized by SEM. Furthermore, two clear relaxations phenomena have been detected using the Nyquist and Argand's plots of dielectric impedance and Modulus curves at different temperatures, which are attributed to both grain and grain boundary contributions. Their activation energies have been calculated not only from the frequency dependence of both imaginary parts of impedance (Z″) and modulus (M″) but also from the contribution of the resistances deduced from the Nyquist plots. These plots have been adjusted using two circuits in series, each of which containing a resistance in parallel to a CEP capacitance. The conduction mechanism was analyzed by ac conduction using the Jonscher's power law. The NSPT conduction model has been confirmed for both compounds in which the rise in heat treatment decreases the binding energy of carriers. [ABSTRACT FROM AUTHOR]

In this work we investigate the effect of Ag+ doping at Sr2+ site in La0.57Nd0.1Sr0.33−xAgxMnO3 (LNSAMOx, x = 0.00 and 0.15) system on the magnetic and magneto-electrical properties. The variation of the magnetization M versus temperature T, at 0.05 T, reveals a ferromagnetic–paramagnetic transition for all samples. All samples undergo a sharp metal–semiconductor transition at a temperature Tρ, accompanying the ferromagnetic–paramagnetic transition. The maximum values of resistivity temperature coefficient (TCR) and magneto-resistance were 2.5% K−1 and 63% at room temperature of 290 K and 305 K, respectively. The TCR value is considered as an important factor in determining the sensitivity of uncooled infrared bolometers. Most interesting is that the adjustment of the low-temperature range ρ–T revealed the presence of low-temperature peaks in the resistivity curves, attributed to the diffusion effects of grain boundaries, electron–electrons, electron–magnon, electron–phonons and the interactions between them. Overall, LNSAMOx polycrystalline ceramics appear promising for uncooled infrared detectors, magnetic memories or magnetic storage devices. [ABSTRACT FROM AUTHOR]

In this research paper, our central focus is upon structural, optic, magnetic, magnetocaloric, and critical phenomena of La0.57Nd0.1Sr0.18Ag0.15MnO3 (LNSMAO) compound. This compound is crystallized in the rhombohedric system, with a R 3 - c space group. The band gap energy of this powder was 2.5 eV. Therefore, the LNSAMO sample proved to be not only a photocatalysis material but also a photovoltaic application. The FTIR spectra confirmed the formation of the structure of orthorhombic perovskite. The second-order transition of the magnetic phase in the LNSMAO sample was also reported by the positive slopes of the Arrott plot. Beneath 5 T, the values of magnetic entropy change and relative cooling power, respectively, amounted to about 5.08 J kg−1 K−1 and 146.7 J/Kg. In perspective, this sample stands for an agreeable candidate for magnetic refrigeration. By analyzing the dependence on the field of the magnetic entropy change (ΔSM) data as well as the relative cooling power (RCP), it was possible to assess the values of the critical exponents. Moreover, the critical exponents of LNSMAO compound were estimated based on multiple techniques like Kouvel-Fisher (KF), modified Arrott plot (MAP) method, and critical isotherm analysis (CIA). The reliability of these critical behaviors was verified by the Widom scaling relation and the universal scaling hypothesis. Our results demonstrate an excellent correlation between magnetocaloric effect (MCE) properties in manganese systems and critical behavior. [ABSTRACT FROM AUTHOR]

A new mixed-valence diphosphate, Zn2+5Fe3+2(P2O7)4, was synthesized from FeII5FeIII2(P2O7)4 via the "solid way" route, by substitution of FeII by ZnII. The obtained X-ray data confirmed the crystallization of the compound in the C2221 symmetry space group (orthorhombic). Magnetic measurements were performed showing that, at room temperature, the compound is paramagnetic and that the Néel temperature is 15.44(20) K. The compound was also investigated by infrared and Raman spectroscopies, in particular to characterize the (P2O7)4− and M–O vibrations. [ABSTRACT FROM AUTHOR]

Two compounds with the formula La0.8Ba0.1Bi0.1FeO3 have been prepared by the sol–gel (LBBFO-SG) and the auto-combustion (LBBFO-AC) preparation methods. The effect of the preparation method on structural, morphology, vibrational, electrical, and dielectric properties have been carried out using the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Raman and impedance spectroscopy. The Rietveld refinement of the XRD diffractograms confirms the crystallization of both compounds through the Pnma space group. Furthermore, the nano-size scale of the prepared compounds was verified by the XRD and the SEM microscopy. From the Raman study, we conclude that the vibration modes are similar to those of the pure LaFeO3 with a slight shape change in some modes. The relaxation processes were analyzed with the Bergmann formalism to validate the presence of two relaxation processes corresponding to grains and boundary grains contributions. These relaxations have been confirmed by studying the dielectric constant also the dielectric loss tangent is used to study the ferroelectric–paraelectric phase transition at around room temperature. The activation energy for both contributions has been calculated from the impedance, the modulus, and the dielectric loss tangent and they have almost the same values. The Nyquist plots (Z″ vs. Z′) have been adjusted using two circuits in series containing each one a resistance in parallel to a CEP capacitance. [ABSTRACT FROM AUTHOR]

In this paper, we present the effect of lanthanum (La) and sodium (Na) vacancies in site A on the morphological, structural, magnetic, and electrical properties of La0,8-x□xNa0,2-x□xMnO3 compounds with x = 0.00, x = 0.05, and x = 0.075 prepared with the sol–gel method. The results of the X-ray powder diffraction diagrams show that these samples crystallize in a rhombohedral structure deformed with the space group R 3 ¯ c, while electron microscopy was carried out for the surface morphology. From the magnetic measurements, the transition from a ferromagnetic (FM) state to a paramagnetic (PM) state in the vicinity of Curie temperature TC is detailed. Moreover, in the electrical part, we study the gap effect on the transition temperature TMI; thus, the nature of the charge transport for the resistance behavior in the different regions (low temperature, metallic, and insulating) has been explained by different models. This work is completed by explaining the two types of magnetoresistance (MR) observed as a function of temperature and applied magnetic field: low-temperature extrinsic magnetoresistance (EMR) and high-temperature intrinsic magnetoresistance (IMR) have been found to be conserved (≈ 30 ℅) with decreasing precursor percentage at room temperature. [ABSTRACT FROM AUTHOR]

The two-dimensional (2d) fully frustrated Planar Rotator model on a square lattice has been the subject of a long controversy due to the simultaneous Z 2 and O(2) symmetry existing in the model. The O(2) symmetry being responsible for the Berezinskii–Kosterlitz–Thouless transition (BKT) while the Z 2 drives an Ising-like transition. There are arguments supporting two possible scenarios, one advocating that the loss of Ising and BKT order take place at the same temperature T t and the other that the Z 2 transition occurs at a higher temperature than the BKT one. In the first case an immediate consequence is that this model is in a new universality class. Most of the studies take hand of some order parameter like the stiffness, Binder's cumulant or magnetization to obtain the transition temperature. Considering that the transition temperatures are obtained, in general, as an average over the estimates taken about several of those quantities, it is difficult to decide if they are describing the same or slightly separate transitions. In this paper we describe an iterative method based on the knowledge of the complex zeros of the energy probability distribution to study the critical behavior of the system. The method is general with advantages over most conventional techniques since it does not need to identify any order parameter a priori. The critical temperature and exponents can be obtained with good precision. We apply the method to study the Fully Frustrated Planar Rotator (FFPR) and the Anisotropic Heisenberg (FFXY) models in two dimensions. We show that both models are in a new universality class with T PR = 0.45286 (32) and T XY = 0.36916 (16) respectively and the transition exponent ν = 0.824 (30) ( 1 ν = 1.22 (4) ). [ABSTRACT FROM AUTHOR]

(La0.8Ca0.2)1−xBixFeO3 (x = 0.0, 0.1, and 0.2) compounds were prepared by the sol-gel method, using the citric acid route. Structural and microstructural characteristics of the samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Mössbauer spectroscopy was also used for magnetic characterization and structural confirmation of X-ray data. Refinement of XRD patterns indicated that the compounds crystallize in an orthorhombic structure, Pnma space group. The SEM measurements showed that the morphology of the samples is characterized by the existence of large agglomerates, while TEM confirmed the fine particle size. Raman spectra revealed that, when increasing temperature, the level of oxygen species adsorbed at the surface of the particles increases progressively. Room temperature Mössbauer spectroscopy data revealed the existence of two octahedral magnetic sites in the structure of the compounds, which is compatible with XRD data, and a small percentage of a paramagnetic phase in the samples, which increases with Bi-content. [ABSTRACT FROM AUTHOR]

Polycrystalline perovskite AMn1−xTiO3 with A = La0.5Pr0.2Sr0.3 (x = 0.0 and 0.1) have been prepared using solid-state reaction method. X-ray powder diffraction and Rietveld refinement revealed that all samples crystallize in a rhombohedral structure with space group R 3 ̄ c From M–T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. The Curie temperature (TC) decreases from 280 to 123 K when the percentage of Ti increases to 10%. The values of the magnetization M(H) decrease when increasing the Ti content. Moreover, the magnetocaloric effect (MCE) was estimated in terms of isothermal entropy change (−ΔSM) using the M(T, μ0H) data and employing the thermodynamic Maxwell equation. In addition, using a phenomenological model, we determine magnetocaloric effect from the calculation of magnetization as a function of temperature under different external magnetic fields. Also, we can determine the relative cooling power (RCP) and the specific heat which varies from 2.803 to 7.354 J/(kg/K) for the undoped sample from M(T, μ0H) data at different magnetic fields theoretically. [ABSTRACT FROM AUTHOR]

Structural studies of Zn2+Fe 2 3 + (P2O7)2 and Cu0.5Zn0.5Fe2(P2O7)2 were made using powder X-ray diffraction and refined by Rietveld method. Both phosphates crystallize in an orthorhombic structure with Pnma space group. Magnetometry measurements showed that below TN = 5.6 (1), Zn2+Fe 2 3 + (P2O7)2 becomes antiferromagnetic and the TN = 14 K is attributed to Cu0.5Zn0.5Fe2(P2O7)2. Mössbauer studies at room temperature and low temperature were performed in both samples. [ABSTRACT FROM AUTHOR]

Topological phase transitions such as the Berezinskii-Kosterlitz-Thouless (BKT) transition are difficult to characterize due to the difficulty in defining an appropriate order parameter or to unravel its critical properties. In this paper, we discuss the application of a newly introduced numerical algorithm that was inspired by the Fisher zeros of the partition function and is based on the partial knowledge of the zeros of the energy probability distribution (EPD zeros). This iterative method has proven to be quite general, furnishing the transition temperature with great precision and a relatively low computational effort. Since it does not need the a priori knowledge of any order parameter it provides an unbiased estimative of the transition temperature being convenient to the study of this kind of phase transition. Therefore, we applied the EPD zeros approach to the 2D XY model, which is well known for showing a BKT transition, in order to demonstrate its effectivity in the study of the BKT transition. Our results are consistent with the real and imaginary parts of the pseudo-transition temperature, T(L), having a different asymptotic behavior, which suggests a way to characterize a BKT like transition. [ABSTRACT FROM AUTHOR]

Coordination compounds of heavier lanthanides with terephthalate ligand have been synthesized and characterized employing simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), TG coupled to FTIR, elemental analysis and complexometry. The results from complexometry with EDTA and from TG curves allowed to establish the stoichiometry of these compounds, which are in agreement with the Ln2(TFTa)3·nH2O general formula where Ln represents trivalent lanthanides or yttrium, TFTA is terephthalate and n = 4 (Er, and Y); 4.5 (Tb, Dy, Ho and Tm); 5 (Yb) and 6.5 (Lu). The thermal decomposition of the anhydrous compounds occurs in two or three consecutive and/or overlapping steps, with the formation of the respective oxides: Tb4O7 and Ln2O3 (Ln = Dy to Lu and Y). The TG-FTIR of the evolved gases obtained from the thermal decomposition of the synthesized compounds, identified the formation of CO2 and water as main gaseous products. The FTIR results also led to information about the type of coordination of the isolated compounds which suggest that the lanthanides are linked to the carboxylate groups by a bridging bond. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has been used in a large range of technological applications, from light-emitting diodes (LEDs) and solar cells to cancer diagnosis and treatment agents. In the last decades, however, a novel antimicrobial property for ZnO particles has been explored, making this oxide an interesting material to be incorporated or deposited on biomaterials, for example in coatings over metallic implants. In this scenario, ZnO physico-chemical properties, mainly particles’ size and morphology, will play fundamental role on its performance. Thus, in this work, two different procedures of a chemical synthesis route named sonochemistry were used to achieve different morphologies/sizes of ZnO. Then, the obtained particles were used to evaluate possible cytotoxic effects against MC3T3-E1 mouse pre-osteoblasts (bone cells). The obtained results indicated that the sonochemical route is an effective way to produce different ZnO morphologies and the way in which these particles interact with osteoblasts (directly or indirectly) may completely influence their cytotoxicity. [ABSTRACT FROM AUTHOR]

Elemental powder mixtures of Fe, Co and Sn of initial compositions FeCoSn(2 ≤y ≤ 26) are ball-milled at high-energy. They yield metastable alloys which are predominantly composed of a supersaturated bcc Fe-Co-Sn phase. The amount of tin dissolved in it is at least ˜15 at.% in the dynamical conditions of milling which were selected. A recently discovered stannide, CoSn, passed hitherto unobserved in Co-Sn binary phase diagrams. It forms at Co-Sn interfaces at very short milling times, 0.5h, thanks to the high-diffusivity of cobalt in tin. Finally, neutron diffraction and Sn Mössbauer spectroscopy show that metastable B2 ordering develops in as-milled alloys, for y ≤ 26, when they are further annealed at modest temperature, here for 15h at 675K. The tendency to long-range order in ternary Fe-Co-Sn bcc alloys is thus observed in metastable alloys. [ABSTRACT FROM AUTHOR]

Recent interest in Fe-Co-Sn alloys stems from Heusler alloys. A CoFeSn Heusler alloy is found to be unstable relative to other phases from ab initio calculations. However, it may be synthesized by non-equilibrium techniques. The present work focuses similarly on metastable ordered phases in ternary Fe-Co-Sn alloys. First, disordered phases of Sn in near-equiatomic Fe-Co are prepared by high-energy ball-milling. As-milled powders are then annealed to possibly produce long-range ordered phases. As-milled powders, of overall composition FeCoSn (2 ≤ x ≤ 34), consist of a single supersaturated bcc phase for x < ~15 at.%. For larger values of x, they are primarily composed of a bcc phase, whose tin content still increases up to ~26 at.%, and of extra phases, which include hexagonal (Fe,Co)Sn. Neutron diffraction patterns and Sn Mössbauer spectra prove that bcc phases of as-milled alloys order to CsCl (B2)-type structures for x ≤ 26 when annealed at 673 K. In addition, Sn Mössbauer spectra reveal that a Sn content of ~15 at.% marks the separation between domains with different short-range orders. From previous and present results, metastable B2 ordering of Sn-rich Co-Fe-Sn alloys is concluded to occur over a significant concentration range. [ABSTRACT FROM AUTHOR]

Fe Mössbauer spectroscopy (MS) and X-ray fluorescence spectroscopy (XRF) were used to determine the identity of iron(III) oxides in surface (top 30 cm ) and subsurface (> 30 cm - 500 cm)sediments from the Helgoland mud area in the German Bight of the North Sea. A 500 cm-long sediment core was cut in 25cm sections while only the top 10 cm of a 30 cm-long sediment core was sampled. Using a MIMOS spectrometer, MS spectra were recorded at 293K (RT) in backscattering geometry. At 80K and 5.5K, MS analysis was carried out in transmission geometry. At RT and 80K only illite was observed, but at 5.5K lepidocrocite was revealed in the MS spectra. The relation between Fe(III) and Fe(II) doublets of illite did not significantly vary with depth, but the relative amount of lepidocrocite increased with depth reaching about 24 % of iron phases, as revealed by MS. XRF measurements showed that the amount of Fe in the sediments varied with depth but was always less than 4 % of total elemental composition. The main component of the sediment was silica and its depth profile alternated with those of other elements, especially aluminium and iron. It was observed that elevated concentrations of dissolved iron in the subsurface sediment of the Helgoland mud area correlated with the depth-wise distribution of distinct microbial populations presumably due to microbial reduction of excess bioavailable iron minerals such as lepidocrocite. These results are thus, important in the context of microbe-mineral interactions in marine sediments as iron oxides are an electron acceptor for microbial anaerobic respiration. [ABSTRACT FROM AUTHOR]

The painting of a rich Jewish merchant 'Bildnis eines jüdischen Kaufmanns' from the Netherlands is dated presumably to the 16 century. After a vivid historical background, i.e. robbed by the Nazis by order of Hermann Göring, it was recently discovered on an Austrian flea market. Different analysis methods were combined to identify the time of the production of this historically interesting looted art. Non-destructive MIMOS II Fe-57 Mössbauer spectroscopy was utilised for mesurements in selected spots. This mainly revealed haematite ( α-FeO) in the red curtain. In spots of the brown jacket Mössbauer spectra indicated the presence of mainly Iron(III) in super-paramagnetic oxide or oxide-hydroxide. Consecutively SEM measurements revealed a restoration by partly over-painting. The elementary composition of the pigments was examined by a portable-X-ray fluorescence. μ-XRF analysis for element distribution at different areas was performed. The look into a crack showed Zinc-white at the bottom of the crack. Traces of Titanium-white could be found within some locations on the surface of the painting. In terms of provenance of the artwork, the presence of Zink-white suggests that the painting was painted around the 19 century. Titanium-white indicates a reconstruction during the 20 century, approximately between 1917 and 1958. [ABSTRACT FROM AUTHOR]

During the years 2004-2007 many Roman amphora sherds were found in the sea near Cortiçais, off the southern coast of the Peniche peninsula on the Atlantic coast of Portugal. The amphorae are of the Haltern 70 type and stem from a shipwreck that has been dated to the time of the emperor Augustus, between about 15 BC and 15 AD. They were produced in the Roman Province of Baetica in the south of Spain and used to transport wine and other staple foods by sea to other Roman settlements. We have studied several fragments of these amphorae by Fe Mössbauer spectroscopy and X-ray diffraction in order to look for changes in the ceramic material caused by two millennia of exposure to sea water. For comparison Mössbauer data on a Haltern 70 type amphora handle excavated on land at the site of Castro do Vieito in the north of Portugal were used. The fragments on which we report here are a body sherd and two handles. The sherds show a visible layer structure. The different layers were studied separately. The Mössbauer spectra of the buff surface layers indicate that up to about 60 % of the iron is present as very fine goethite particles, which are superparamagnetic at RT but exhibit magnetically split spectra at 4.2 K. Their blocking temperature is around or even below 50 K. The goethite is too fine grained to be detected by X-ray diffraction. Re-firing experiments confirm the presence of goethite, which is found to convert to hematite between 300 and 600 C. The results show that the iron in the silicate matrix of the ceramic material converts to goethite under the prolonged influence of the sea water, mainly in the outermost several millimetres and apparently depending on the nature of the ceramic material. [ABSTRACT FROM AUTHOR]

A library of microorganisms originating from various marine environments in French Polynesia was screened for polyhydroxyalkanoate producing bacteria. No significant connection was found between the geo-ecological source of bacteria and their ability to produce polyhydroxyalkanoate. A bacterial strain designated as Enterobacter FAK 1384 was isolated from a shark jaw. When grown on coprah oil, this bacterium produces a PHA constituting of 62 mol % 3-hydroxydecanoate and lower amount of 12 mol % 3-hydroxydodecenoate and of 7.6 mol % 3-hydroxydodecanoate. These interesting properties make this mcl-PHA a good candidate for further exploitations in many industrial sectors, as in film and coating manufacturing, as well as for biomedical applications. [ABSTRACT FROM AUTHOR]

The knowledge of Hg concentrations in fish is of considerable interest since these organisms are a major source of protein to coastal human populations and fishing communities. The main source of human exposure to Hg contamination occurs through the consumption of fish. In this paper, we compare Hg concentration in 13 fish species from Jaguaribe River lower basin and an adjacent coastal region in the northeastern coast of Brazil. We sampled fish from three stretches of the river: fluvial, estuarine, and marine regions. We tested the hypothesis that Hg concentration in muscle tissue vary according to species, location, and trophic level. Significant differences were observed among species and trophic level, but these could not be observed among the regions studied. As expected, the highest concentrations were observed in carnivorous fish (5.6-107.5; 26.9 ± 18.8 ng g). Hg concentrations observed in this study are similar to those observed in regions of low environmental contamination. We estimated Hg intake to vary between 0.02 and 0.22 ng Hg kg body weight week, for the average body weight of 56.7 kg, which was considered as low exposure and therefore, a low risk to consumers of fish from the regions studied. [ABSTRACT FROM AUTHOR]

Indigenous, introduced and farmed fish species were collected from the Jaguaribe Basin, NE Brazil to assess total and methyl mercury concentrations in muscle tissue and to determine its relationship with fish origin. The results obtained from introduced species were compared to the Hg content of their original area of occurrence, which is located in the Amazon region. Farmed and wild individuals of Oreochromis niloticus (tilapia) were also compared. Introduced species presented lower Hg contents compared to their Amazonian counterparts. Wild individuals of O. niloticus also presented higher Hg contents than farmed individuals with similar sizes. However, methyl Hg concentrations were not significantly different between the two groups. Total Hg and methyl Hg concentrations were higher in carnivorous species, especially those from the Amazon region, and surpassed the Brazilian guidelines for fish consumption. Based on their Hg content, Jaguaribe basin fish do not pose a significant threat to human consumption. [ABSTRACT FROM AUTHOR]

The long lost painting 'Trumpeting Putto' was discovered and now is not only in the focus of art historian, but has also scientific interest too. We underwent this rare case of an inorganic layered artwork a non-destructive material investigation by employing Raman and MIMOSII Fe-57 Mössbauer spectroscopy. First results indicate several layers, where two layers of different pigments are on an inorganic background layer stabilised by a metallic wire within a wooden frame structure [ABSTRACT FROM AUTHOR]