Cerium Tetrafluoride: Sublimation, Thermolysis, and Atomic Fluorine Migration.

Saturated vapor pressure p° and enthalpy of sublimation (ΔsH°) of cerium tetrafluoride CeF4 were determined by means of Knudsen effusion mass spectrometry in the range of 750-920 K. It was discovered that sublimation of cerium tetrafluoride from a platinum effusion cell competes with thermal decomposition to CeF3 in the solid phase, but no accompanying release of fluorine to the gas phase occurs. Thus, fluorine atoms migrate within the surface layer of CeF4(s) to the regions of their irreversible drain. We used scanning electron microscopy to study the distribution of the residual CeF3(s) across the inner surface of the effusion cell after complete evaporation of CeF4(s). It was observed that CeF3 accumulates near the edge of the effusion orifice and near the junction of the lid and the body of the cell, that is, in those regions where the fluorine atoms can migrate to a free platinum surface and thus be depleted from the system. Distribution of CeF3(s) solid particles indicates the ways of fluorine atoms migration providing CeF3(s) formation inside the CeF4(s) surface layer.

Immunological Distinctions between Acellular and Whole-Cell Pertussis Immunizations of Baboons Persist for at Least One Year after Acellular Vaccine Boosting.

While both whole-cell (wP) and acellular pertussis (aP) vaccines have been highly effective at reducing the global pertussis disease burden, there are concerns that compared to wP vaccination, the immune responses to aP vaccination may wane more rapidly. To gain insights into the vaccine elicited immune responses, pre-adult baboons were immunized with either aP or wP vaccines, boosted with an aP vaccine, and observed over a nearly two-year period. Priming with a wP vaccine elicited a more Th17-biased response than priming with aP, whereas priming with an aP vaccine led to a more Th2-biased response than priming with wP. These differences were maintained after aP vaccine boost immunizations. Compared to aP, animals primed with a wP vaccine exhibited greater numbers of pertussis specific memory B cells. While aP and wP vaccine priming initially elicited similar levels of anti-pertussis toxin antibody, titers declined more rapidly in aP vaccine primed animals leading to a 4-fold difference. Both wP and aP vaccine immunization could induce serum bactericidal activity (SBA); however, only one wP vaccine immunization was required to elicit SBA while multiple aP vaccine immunizations were required to elicit lower, less durable SBA titers. In conclusion, when compared to aP vaccine, priming with wP vaccine elicits distinct cellular and humoral immune responses that persist after aP vaccine boosting.

Sonochemically assisted synthesis of zinc-doped maghemite.

Nanoparticles of zinc-doped maghemite were prepared using ultrasonic radiation. As a precursor, a suspension of maghemite in an alkaline aqueous solution of zinc nitrate at pH 9 was sonicated. The zinc-doped maghemite nanoparticles were investigated by X-ray diffraction, Mössbauer spectroscopy, high-resolution electron microscopy (HREM) and SQUID magnetometry. The Mössbauer measurements, which cover the temperature range 4.2 K to room temperature, were acquired in zero field and an applied field of 5 T. The results show that by using ultrasound radiation, zinc Zn2+ can substitute for Fe3+ up to a composition close to zinc ferrite (ZnFe2O4), which has a random distribution of Fe3+ ions over both A and B sublattices in the spinel structure with an inversity parameter of delta=0.322. This leads to a maximum saturation magnetization (Ms) of 64.1 emu/g at 300 K and 73.5 emu/g at 2 K.

Exchange bias in bulk layered hydroxylammonium fluorocobaltate (NH3OH)2CoF4.

The magnetic properties of layered hydroxylammonium fluorocobaltate (NH(3)OH)(2)CoF(4) were investigated by measuring its dc magnetic susceptibility in zero-field-cooled (ZFC) and field-cooled (FC) regimes, its frequency dependent ac susceptibility, its isothermal magnetization curves after ZFC and FC regimes, and its heat capacity. Effects of pressure and magnetic field on magnetic phase transitions were studied by susceptibility and heat capacity measurements, respectively. The system undergoes a magnetic phase transition from a paramagnetic state to a canted antiferromagnetic state exhibiting a weak ferromagnetic behavior at T(C) = 46.5 K and an antiferromagnetic transition at T(N) = 2.9 K. The most spectacular manifestation of the complex magnetic behavior in this system is a shift of the isothermal magnetization hysteresis loop in a temperature range below 20 K after the FC regime-an exchange bias phenomenon. We investigated the exchange bias as a function of the magnetic field during cooling and as a function of temperature. The observed exchange bias was attributed to the large exchange anisotropy which exists due to the quasi-2D structure of the layered (NH(3)OH)(2)CoF(4) material.