The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

The 3 and 4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The 4 band shows extremely sharp lines of a width of ϳ0.003 cm Ϫ1 , while the 3 band exhibits broader lines of a width of 1 cm Ϫ1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.

Methyl iodide is trapped as the monomer and as clusters in the parahydrogen, known as a quantum crystal, at temperatures below about 8 K. UV illumination of the deposited sample at about 5 K causes the dispersal of clusters and the production of the methyl radical, methane, and ethane as evidenced by their infrared absorption spectra. Thermal annealing of the photolyzed sample at temperatures up to 11 K results in the disappearance of the methyl radical, the enhancement of ethane, and the regeneration of methyl iodide. When the initial concentration of the iodide is small, the clusters in the deposited sample are suppressed. For such a sample the UV excitation produces the methyl radical and methane but the formation of ethane is negligibly small. Relevance of the present work to studies of photolysis in gaseous clusters of methyl iodide is discussed.

Small carbon clusters produced by laser ablation of a carbon rod are trapped in solid parahydrogen at 4.8 K. Infrared spectra show the presence of C3, C5, C9, and a few new clusters. The observed vibrational spectra with multiplet structures are tentatively associated with hindered rotation of the clusters. Temperature dependence of the IR spectra reveals the diffusion of C3 and C5 clusters in the crystal at around 8 K, while no diffusion of C9 and the larger clusters is noticed. Any hydrocarbons which might be produced by reactions between the carbon clusters and the substrate hydrogen molecules are not observed both during the deposition and after the thermal annealing.

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Solid parahydrogen is an excellent matrix for matrix-isolation spectroscopy because of its high spectral resolution. Here we describe the rovibrational structure and nuclear spin conversion of CH4 embedded in parahydrogen crystals studied by infrared absorption spectroscopy. The vibration–rotation absorptions of CH4 exhibit time-dependent intensity changes at 4.8 K. These changes are interpreted to be a result of the I=1→I=2 nuclear spin conversion that accompanies the J=1→J=0 rotational relaxation. The half-lifetime of the upper J=1 rotational state is unchanged by the addition of up to 2% orthohydrogen molecules but decreases with more than 10% orthohydrogen molecules. The increase of the decay rate at higher orthohydrogen concentration indicates that the magnetic field gradient across CH4 due to the orthohydrogen molecules mixes the nuclear spin states, which accelerates the conversion.

This work presents a structural and magnetic study of NiFe2O4 nanoparticles. Powder samples with different particle sizes were made by annealing the fine powder at different temperatures. X-ray diffraction, transmission electron microscopy, and low temperature SQUID magnetometry experiments were carried out to characterize the samples. Results support a previously proposed model that the NiFe2O4 nanoparticle has a core/shell structure due to surface disorder. However, a detailed analysis of the data reveals that although the structural disorder in the surface of the particle is the major cause for forming a shell, the superexchange coupling is the driving force for the magnetic configuration, which creates a magnetically immobilized region near the surface region with thicknesses significantly larger than that of the structurally inhomogeneous layer on the surface. Also, the ease of magnetization of the core can be significantly affected. Since the crystalline and magnetic disorders commonly exist in the surface region of magnetic nanoparticles, one has to wisely utilize the exchange coupling in the development of nanomagnetic materials.

To prevent fixation defects or artifacts in the whole bodies of fish caused by conventional fixatives, such as formalin solution, Bouin’s fluid (BF), and Davidson’s fluid (DF), the optimal fixatives and fixing method were examined. An improved method of fixing the whole bodies of fish was examined that makes use of a combination of 20% formalin and BF or DF. The fixatives were examined with four representative tissues, i.e., the gill, liver, intestinal tract, and kidney, to evaluate end points including the appearance of degraded tissues and artifacts caused by each fixative, overall morphological clarity of nuclei, staining intensity, and integrity of the other tissues. The best results were obtained when the fresh whole bodies were initially fixed in 20% formalin (primary fixation) at 4°C for 1 h and subsequently fixed in BF for 5 h at 4°C (secondary fixation). Therefore, the current findings led the authors to conclude that the combination of primary fixation with 20% formalin at 4°C for 1 h and secondary fixation with BF at 4°C for 5 h was suitable for fixation of the whole bodies of fish.