[en] This paper presents an investigation on the heat transfer characteristics associated with liquid-gas Taylor flows in mini channels incorporating microencapsulated phase change materials (MPCM). Taylor flows have been shown to result in heat transfer enhancements due to the fluid recirculation experienced within liquid slugs which is attributable to the alternating liquid slug and gas bubble flow structure. Microencapsulated phase change materials (MPCM) also offer significant potential with increased thermal capacity due to the latent heat required to cause phase change. The primary aim of this work was to examine the overall heat transfer potential associated with combining these two novel liquid cooling technologies. By investigating the local heat transfer characteristics, the augmentation/degradation over single phase liquid cooling was quantified while examining the effects of dimensionless variables, including Reynolds number, liquid slug length and gas void fraction. An experimental test facility was developed which had a heated test section and allowed MPCM-air Taylor flows to be subjected to a constant heat flux boundary condition. Infrared thermography was used to record high resolution experimental wall temperature measurements and determine local heat transfer coefficients from the thermal entrance point. 30.2% mass particle concentration of the MPCM suspension fluid was examined as it provided the maximum latent heat for absorption. Results demonstrate a significant reduction in experimental wall temperatures associated with MPCM-air Taylor flows when compared with the Graetz solution for conventional single phase coolants. Total enhancement in the thermally developed region is observed to be a combination of the individual contributions due to recirculation within the liquid slugs and also absorption of latent heat. Overall, the study highlights the potential heat transfer enhancements that are attainable within heat exchange devices employing MPCM Taylor flows.

[en] The crystal packing of a number of styryl dyes of the pyridine series is analyzed. The structures of three dyes and three [2 + 2] photocycloaddition (PCA) products, 1,2,3,4-tetrasubstituted cyclobutanes, obtained in single crystals are determined by X-ray diffraction. Stacks of planar organic cations are characteristic of styryl dye packings. The proceeding of the PCA reaction as a single crystal-to-single crystal transformation in the syn head-to-head stacks is in principle impossible. The syn head-to-tail stacking packings are favorable for the PCA reactions resulting in the centrosymmetric rctt isomers of cyclobutane. The stacking packings, in which molecules are related by the twofold axes (the anti arrangement of molecules), are also favorable for PCA in single crystals. In this case, the products are the rtct isomers of cyclobutane. The presence of the I^- counterions in a packing is a factor impeding the PCA reaction, because the secondary I-H-C bonds increase the rigidity of the crystal lattice. The conditions necessary for proceeding the PCA reactions in styryl dyes as single crystal-to-single crystal processes are as follows: (1) the stacks split into pairs of organic cations (dimers) with the d distances within 4.2 A in a dimer and d exceeding 4.2 A between the dimers; and (2) the dimers are surrounded by flexible shells consisting of anions, solvate molecules, or flexible moieties of the organic cations themselves.

[en] Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of ¹³²Sn, ¹³⁰Sn, and ¹³⁴Te and deuterated polyethylene targets. Preliminary results are presented. The Q-value spectra for ¹³³Sn, ¹³¹Sn and ¹³⁵Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf_7/2 nature of the ground state of ¹³³Sn, and 2p_3/2 for the 3.4 MeV state in ¹³¹Sn.

[en] The nature and the mechanism of the magnetic hysteresis for the thermal spin crossover exhibited by an iron (II) compound is investigated by means of variable-temperature powder and single-crystal x-ray diffraction. The unit cell temperature dependence clearly evidences the amplitude of the strong structural rearrangement that accompanies the spin crossover-corresponding to a variation of 8.6% for one of the unit cell parameters-as well as the structural hysteresis width. In this regard, the present x-ray study reveals significant differences in the spin crossover features according to the nature of the sample-powder or single crystal-that should be taken into account in the analysis of physical properties. Concerning the interplay between structural and magnetic transitions, quenching effects show that the structural transition and the spin crossover are indissociable. Furthermore, investigations of the mechanism itself of the thermal spin crossover confirm the presence of spin-like domains in the conversion region, either in the cooling or in the warming loops. The non-dependence with temperature of these domains inside the hysteresis loop demonstrates the stability of the microscopic and macroscopic structures in the corresponding thermodynamic conditions. This result is of interest in the context of the potential use of hysteresis loops to obtain high-temperature photo-conversion

[en] The ²⁸Si(p,t)²⁶Si reaction has been studied to resolve a controversy surrounding the properties of the ²⁶Si level at 5.914 MeV and its contribution to the ²⁵Al(p,γ)²⁶Si reaction rate in novae, which affects interpretations of galactic ²⁶Al observations. Recent studies have come to contradictory conclusions regarding the spin of this level (0⁺ or 3⁺), with a 3⁺ assignment implying a large contribution by this level to the ²⁵Al(p,γ)²⁶Si reaction rate. We have extended our previous study [Bardayan et al., Phys. Rev. C 65, 032801(R) (2002)] to smaller angles and find the angular distribution of tritons populating the 5.914-MeV level in the ²⁸Si(p,t)²⁶Si reaction to be consistent with either a 2⁺ or 3⁺ assignment. We have calculated reaction rates under these assumptions and used them in a nova nucleosynthesis model to examine the effects of the remaining uncertainties in the ²⁵Al(p,γ)²⁶Si rate on ²⁶Al production in novae