Redistribution of population among the higher levels of Na atoms in an H2-O2-Ar flame

A substantial fraction of the population of Na-atoms in an H₂-O₂-Ar flame is found to be distributed among the higher levels as a result of two-photon laser excitation, spontaneous emission and collisions with flame gas atoms and molecules. Several population inversions are observed. From the laser-excited level upwards, a partial Boltzmann equilibrium, corresponding to the flame temperature, has been found in some cases. Estimates of weighted average rate-constants for collisional energy transfer from groups of higher levels to the 3P-level are given. Some level-pairs appear to be strongly coupled to each other.     

Electronic-excitation transfer collisions in flames-III: Cross sections for quenching and doublet mixing of Rb(52P32, 12) doublet by N2, O2, H2 and H2O

Weighted average quenching cross sections for the Rb(5²P) doublet by N₂ and H₂O were determined in flames with temperatures ranging from 1500 to 2500 K by measuring the fluorescence efficiency. The values found are $\text{(σ}{}_{\mathrm{qu}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (19±2)}\text{A}\text{?}{}^2$ and over the entire temperature range. At a temperature of 1720 K, mixing cross sections were obtained for the same doublet with N₂, H₂, O₂ and H₂O molecules. The cross sections found are: $\text{σ}{}_{21}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (60±12)}\text{A}\text{?}{}^2$, $\text{σ}{}_{12}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= 99±20)}\text{A}\text{?}{}^2$; , $\text{(σ}{}_{21}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 30}\text{A}\text{?}{}_2$, $\text{(σ}{}_{12}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 50}\text{A}\text{?}{}^2\text{;}$, . The ratios σ₁₂/σ₂₁ were measured independently and were found to agree with the detailed- balance condition within 3 per cent. A critical comparison of the flame values with previous literature data on N₂-cross sections shows that both mixing and quenching cross sections are temperature dependent in the range from 300 to 2500 K.     

Experimental characteristics of direct current and high frequency boosted hollow cathode lamps

Two types of boosted output hollow cathode lamps, viz. direct current and high frequency boosted lamps, were investigated and the characteristics compared. Both lamps are demountable and use the same water-cooled cathode holder. Remarkably similar results were obtained for both types of booster discharges with respect to intensity enhancement of various spectral lines of a number of elements, and with respect to line widths, which were measured with a Fabry-Perot interferometer for strontium only. The interferometer measurements also revealed that although the gain in total intensity for Sr is only about a factor of 8, the gain in intensity at line centre is approximately a factor 40. Although the intensity enhancement caused by the booster discharges is relatively small (～ a factor of 10) for resonance lines in the visible region, the absolute intensities of these lines are much higher than those of lines in the ultraviolet.     

Thermoelectric power generation in a thermoacoustic refrigerator

Commercially available solid-state thermoelectric devices may be used for their electrical power generation capabilities when coupled to a thermoacoustic refrigerator or heat pump. General performance characteristics as well as bulk thermal conductivity for a selection of thermoelectric elements was first found by using a two-plate apparatus to maintain a constant temperature difference across the element. Further studies of an element’s performance when placed in series with the thermoacoustic refrigerator’s heat exchangers will be presented. Design considerations for using thermoelectric elements in a no-moving parts electrical power generation scheme will be discussed.     

Determination of rates of collision-induced vibrational and intramultiplet transitions for YO(A2II) molecules in Ar- and N2-diluted flames

Rate contants for single-step collisional transitions between specified vibrational and electronic-doublet levels of YO(A²II) molecules were determined under multiple-collision conditions at constant total gas pressure. We recorded simultaneously the thermal emission spectrum and the fluorescence spectra induced by a cw dye laser tuned successively at various vibronic transitions. We used premixed N₂-diluted or Ar-diluted H₂-O₂ flames at 1 atm and = 2350 K, containing YO vapour. Relative rate constants (normalized to the quenching plus radiative de-excitation rate constants) were obtained by solving a set of simultaneous master equations involving the stationary laser-induced population increments. Absolute rate constants were derived therefrom by determining indirectly the fluorescence efficiency. Exoergic doublet-mixing collisions appeared to have greater probabilities than Δv = ?1 or ?2 transitions and were about equally probable as quenching collisions. Ar and N₂ were about equally efficient as collision partner. The rate constants of each process and of its reverse were compared with detailed-balance. The rotational levels in the pumped band appeared to preserve the e/f symmetry index partially.     

A theoretical investigation of the interaction between substituted carbonyl derivatives and water: Open or cyclic complexes?

The structures and binding energies of complexes between substituted carbonyl bases and water are the B3LYP/6‐311++G(d,p) computational level. The calculations also include the proton affinity (PA) of the O of the C?O group, the deprotonation enthalpies (DPE) of the CH bonds along a natural bond orbital analysis. The calculations reveal that stable open C?O···H_wO_w as well as cyclic CH···O_wH_w···O?C complexes are formed. The binding energies for the open complexes are linearly related to the PAs, whereas the binding energies for the cyclic complexes depend on both the PA and DPE. Different indicators of hydrogen bonds strength such as electron charge density, intramolecular and intermolecular hyperconjugation energy, occupation of orbitals, and charge transfer show significant differences between open and cyclic complexes. The contraction of the CH bond of the formyl group and the corresponding blue shift of the ν(CH) vibration are explained by the classical trans lone pair effect. In contrast, the elongation or contraction of the CH₃ group involved in the interaction with water results from the variation of the orbital interaction energies from the σ(CH) bonding orbital to the σ* and π* antibonding orbitals of the C?O group. The resulting blue or red shifts of the ν(CH₃) vibrations are calculated in the partially deuterated isotopomers. © 2012 Wiley Periodicals, Inc.     

Rupture of thin liquid films induced by impinging air-jets

Thin liquid films on partially wetting substrates are subjected to laminar axisymmetric air-jets impinging at normal incidence. We measured the time at which film rupture occurs and dewetting commences as a function of diameter and Reynolds number of the air-jet. We developed numerical models for the air flow as well as the height evolution of the thin liquid film. The experimental results were compared with numerical simulations based on the lubrication approximation and a phenomenological expression for the disjoining pressure. We achieved quantitative agreement for the rupture times. We found that the film thickness profiles were highly sensitive to the presence of minute quantities of surface-active contaminants.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.