Magnetic susceptibility studies of the spin-glass and Verwey transitions in magnetite nanoparticles

Magnetite nanostructured powder samples were synthesized by aging chemical method. Phase, structural, and magnetic properties were characterized. X-ray diffraction patterns showed cubic magnetite pure phase, with average crystallite size, , equal to 40 nm. Susceptibility measurements showed the well-known Verwey transition at a temperature of 90 K. The decrease of Verwey transition temperature, with respect to the one reported in literature (125 K) was attributed to the low average crystallite size. Moreover, the spin-glass like transition was observed at 35 K. Activation energy calculated from susceptibility curves, with values ranging from 6.26 to 6.93 meV, showed a dependence of spin-glass transition on frequency. Finally, hysteresis loops showed that there is not an effect of Verwey transition on magnetic properties. On the other hand, a large increase of coercivity and remanent magnetization at a temperature between 5 and 50 K confirmed the presence of a magnetic transition at low temperatures

Synthesis of Hierarchical Dorsal Spine Ag

Silver sulfide hierarchical structures with unique dorsal spine morphology were successfully synthesized on mechanically deformed silver substrates by simple solid-vapor reactions. It has been found that it is possible to change the structures morphology by changing the reagent gas composition. The carbon monoxide (CO) presence in a reactive sulfur atmosphere was found to be the key for growing the dorsal spine structures. In all cases, the Ag2S structures grew on the edge of the silver substrates where high plastic deformation occurred

Superparamagnetic response of zinc ferrite incrusted nanoparticles

Zinc ferrite is synthesized via mechano-activation, followed by thermal treatment. Spinel ZnFe2O4 single phase is confirmed by X-ray diffraction. SEM micrographs show large particles with average particle size 〈Dpart〉 = 1 μm, with particles in intimate contact. However, TEM micrographs show incrusted nanocrystallites at the particles surface, with average nanocrystallite size calculated as 〈Dinc〉 ≈ 5 nm. The blocking temperature at 118 K in the ZFC-FC curves indicates the presence of a superparamagnetic response which is attributable to the incrusted nanocrystallites. Moreover, the hysteresis loops show the coexistence of superpara- and paramagnetic responses. The former is observable at the low field region; meanwhile, the second one is responsible of the lack of saturation at high field region. This last behavior is related to a paramagnetic contribution coming from well-ordered crystalline microdomains. The hysteresis loops are analyzed by means of two different models. The first one is the susceptibility model used to examine separately the para- and superparamagnetic contributions. The fittings with the theoretical model confirm the presence of the above mentioned magnetic contributions. Finally, using the Langevin-based model, the average superparamagnetic diameter 〈DSPM〉 is calculated. The obtained value 〈DSPM〉 = 4.7 nm (∼5 nm) is consistent with the average nanocrystallite size observed by TEM.Authors would like to acknowledge to the Universidad Autónoma de Ciudad Juárez, México and Instituto de Magnetismo Aplicado, UCM, Spain for the support given to this research work. This research was supported by UACJ research fund and CONACYT-FOMIX project with Registry No. CHIH-2011-C03-174099

Initial invasive or conservative strategy for stable coronary disease

BACKGROUND Among patients with stable coronary disease and moderate or severe ischemia, whether clinical outcomes are better in those who receive an invasive intervention plus medical therapy than in those who receive medical therapy alone is uncertain. METHODS We randomly assigned 5179 patients with moderate or severe ischemia to an initial invasive strategy (angiography and revascularization when feasible) and medical therapy or to an initial conservative strategy of medical therapy alone and angiography if medical therapy failed. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest. A key secondary outcome was death from cardiovascular causes or myocardial infarction. RESULTS Over a median of 3.2 years, 318 primary outcome events occurred in the invasive-strategy group and 352 occurred in the conservative-strategy group. At 6 months, the cumulative event rate was 5.3% in the invasive-strategy group and 3.4% in the conservative-strategy group (difference, 1.9 percentage points; 95% confidence interval [CI], 0.8 to 3.0); at 5 years, the cumulative event rate was 16.4% and 18.2%, respectively (difference, 121.8 percentage points; 95% CI, 124.7 to 1.0). Results were similar with respect to the key secondary outcome. The incidence of the primary outcome was sensitive to the definition of myocardial infarction; a secondary analysis yielded more procedural myocardial infarctions of uncertain clinical importance. There were 145 deaths in the invasive-strategy group and 144 deaths in the conservative-strategy group (hazard ratio, 1.05; 95% CI, 0.83 to 1.32). CONCLUSIONS Among patients with stable coronary disease and moderate or severe ischemia, we did not find evidence that an initial invasive strategy, as compared with an initial conservative strategy, reduced the risk of ischemic cardiovascular events or death from any cause over a median of 3.2 years. The trial findings were sensitive to the definition of myocardial infarction that was used

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline