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The production of gas-phase complexes by radiative association is a strongly temperature-dependent process, whose modeling offers a good test of theoretical techniques to modeling the kinetics and whose predictability is helpful for temperature extrapolations. The temperature dependence of the low-pressure association rate constants, measured in the Fourier transform ion cyclotron resonance mass spectrometer, was examined for four systems, namely, acetone/(acetone)H+, acetone-d6/(acetone-d6)D+, butanone/(butanone)H+ and NO+/3-pentanone.

The hydrophobic hydration of dimethylsulfoxide (DMSO)/D[sub 2]O was explored using a combination of the high-pressure method and ab initio calculations. The frequencies of the C-H stretching vibration of DMSO increase as the mole fraction of D[sub 2]O increases, while no appreciable changes in spectral shapes are observed upon dilution. Interestingly, the infrared spectra of DMSO/D[sub 2]O observed under high-pressure exhibits dramatic changes, while the new spectral features locating at ∼2942 and ∼3033 cm[sup -1] appear. The spectral changes were attributed to the combined effect of C-H-O hydrogen bonding between C-H in DMSO and oxygen atom in D[sub 2]O, a phase change, pressure increase, etc. Ab initio calculation results, forecasting the frequency shift of the C-H stretching vibration as C-H-O is interacting via hydrogen bonding, are discussed. The reorganization of the hydrogen-bond network or geometry may be responsible for spectral changes as the pressure was elevated. [ABSTRACT FROM AUTHOR]

Various aspects of the theory and modeling of ion–molecule radiative association are discussed. A general formalism for evaluating the effective rate constant for radiative and collisional association is reviewed. The implementation of variable reaction coordinate transition state theory estimates within this formalism is described. A detailed discussion is given of the limiting cases of high and low stabilization efficiency. The basic validity of the algorithm is illustrated through sample calculations for the high efficiency limit. The low efficiency limit allows for the determination of binding energies which are independent of any transition state model. The relation between the predicted and observed temperature dependence in the low efficiency limit is explored. Sample calculations employing the general formalism illustrate the usefulness of this modeling in estimating the binding energy of the complex. Modest levels of quantum chemistry (e.g., MP2/6-31G*) are found to provide satisfactory estimates of the vibrational frequencies and intensities required in the modeling. Overall, the modeling provides estimated binding energies for the protonated acetone dimer, NO+...3-pentanone, and Al+...C6H6 complexes which agree with the available literature values to within 2 kcal/mol. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. In this study, we investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. Downlink power control scheme and two power control methods for uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for microcell are also noted, such as more power transmitted by a microcell base station (BS) should be paid if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by uplink and downlink, respectively. With downlink power control, microcellular capacity can be increased. However, combining of downlink power control for microcell and C/I uplink power control for macrocell causes the overall system capacity to significantly increase. Index Terms - Blocking probability, hierachical layer of cells, homogeneous structure, power control, service hole area.

The fine water droplet size spray is recognized as a perfect fire suppression media for most fire accidents. Due to the undissolvable property with water for common use petrochemical substances, such as methanol, diesel and heptane, the water droplet size may severely influence the liquid fire extinguished effect with water spray. Therefore, an appropriate water droplet size range shall be understood for better fire extinguished effect design. An experimental program was investigated using laser particle diameter analyzer (PDA) to examine the test water droplet size under six different water supply pressures. A single water spray head was installed under the ceiling at a constant distance. The experimental results show that a water droplet size less than 700 μm may provide a better liquid pool fire extinguished effect for one liter liquid under a constant water flow rate test condition. However, it should be noted that the results are limited to the experimental conditions. [ABSTRACT FROM AUTHOR]