Multiple hindered rotators in a gyroscope-inspired tribenzylamine hemicryptophane

A gyroscope-inspired tribenzylamine hemicryptophane provides a vehicle for exploring the structure and properties of multiple p-phenylene rotators within one molecule. The hemicryptophane was synthesized in three steps in good overall yield using mild conditions. Three rotator-forming linkers were cyclized to form a rigid cyclotriveratrylene (CTV) stator framework, which was then closed with an amine. The gyroscope-like molecule was characterized by (1)H NMR and (13)C NMR spectroscopy, and the structure was solved by X-ray crystallography. The rigidity of the two-component CTV-trismethylamine stator was investigated by (1)H variable-temperature (VT) NMR experiments and molecular dynamics simulations. These techniques identified gyration of the three p-phenylene rotators on the millisecond time scale at -93 °C, with more dynamic but still hindered motion at room temperature (27 °C). The activation energy for the p-phenylene rotation was determined to be ~10 kcal mol(-1). Due to the propeller arrangement of the p-phenylenes, their rotation is hindered but not strongly correlated. The compact size, simple synthetic route, and molecular motions of this gyroscope-inspired tribenzylamine hemicryptophane make it an attractive starting point for controlling the direction and coupling of rotators within molecular systems.     

Mixing enhancement in a multi-stream injection nozzle

We present quantitative analysis of image sequences of multi-stream injection nozzle flows with several different injection geometries in an experiment simulating mixing in a chemical oxygen-iodine laser. To visualize mixing, image sequences were acquired with planar laser-induced fluorescence (PLIF) in iodine that was injected into the main flow. The injection nozzle consisted of a slot, ejector, and injector block, with rows of ejector and injector holes along the slot length. The ejector flow exits in an underexpanded state so that upon expanding it forces the slot and injector flows together to enhance mixing. For this study, the diameter and geometry of ejector holes were varied to assess their effect on mixing. Two configurations of ejector holes were used, each with two different diameters for a total of four cases with data collected at downstream stations. We carry out a quantitative mixing analysis for these configurations, using two methods to quantify the mixing. The first method considers the statistics of the PLIF image intensity histograms, which are bimodal for poorly-mixed flows and have a single peak in well-mixed flows. The second method quantifies the properties of the mixing interface. Our analysis shows that two injection schemes significantly enhance mixing by stretching the mixing interface.     

Singing power ratio: Quantitative evaluation of singing voice quality

This paper presents a parameter for objectively evaluating singing voice quality. Power spectrum of vowel sound / a / was analyzed by Fast Fourier Transform. The greatest harmonics peak between 2 and 4 kHz and the greatest harmonics peak between 0 and 2 kHz were identified. Power ratio of these peaks, termed singing power ratio (SPR), was calculated in 37 singers and 20 nonsingers. SPR of sung / a / in singers was significantly greater than in nonsingers. In singers, SPR of sung / a / was significantly greater than that of spoken / a /. By digital signal processing, power spectrum of sung / a / was varied, and the processed sounds were perceptually analyzed. SPR had a significant relationship with perceptual scores of “ringing” quality. SPR provides an important quantitative measurement for evaluating singing voice quality for all voice types, including soprano.     

Ninhydrin as a building block for yohimbanones, β-carbolines, and oxyprotoberberines

Condensation of ninhydrin with tryptamide or tryptamine followed by Lewis acid-induced rearrangement provided yohimbanones that were readily converted to β-carbolines via oxidative ring cleavage. The analogous condensation-rearrangement with 3,4-dimethoxyphenethylamine and ninhydrin afforded an oxyprotoberberine, which was further oxygenated at the 13a position.     

Mental Computation of Students in a Reform-Based Mathematics Curriculum

Traditional school instruction in mathematics has generally produced students who are poor at mental computation and exhibit a weak sense of number and mathematical operations. In this study, fifth graders who had been in a reform-based mathematics curriculum since kindergarten were given a whole-class test on mental computation problems. Baseline data with students in traditional mathematics curricula were used as a comparison. The students in this reform-based mathematics curriculum performed much higher than the comparison group on all but one problem, and on most problems, this difference was substantial. Additionally, a student preference survey indicated that students in the reform curriculum were more likely to consider the calculator as an option than were the baseline group. They were also more able to recognize problems that did not lend themselves to mental computation. Individual interviews indicated that experiences in the primary grades with “invented” algorithms and discussing alternative solutions led to a better ability to compute mentally and a stronger number sense.     

Limits on spurious contributions to integrated crosssections for photoexcitation and de-excitation of isomers

The large values of integrated cross sections for the excitation and de-excitation of nuclear isomers in (γ, γ′) reactions provide strong encouragement for the feasibility of an optically pumped gamma-ray laser. For this reason, sources of possible spurious contamination of the measurements were carefully considered. This paper reviews an analysis of possible sources as well as experimental limits on contamination of the isomeric yields. The question of spurious contributions from (n, γ) or (n, n′) reactions was examined by estimating the level of thermal, epithermal and fast neutron fluxes based on possible source material in the accelerator environments. Such possibilities were severely reduced by the range of photon energies employed in the studies of 1.5-6 MeV. The expected fluxes were below levels necessary to produce significant isomeric yields in this energy range. Next, experiments were conducted in accordance with standard neutron activation-foil techniques to directly measure any fluxes of neutrons in the accelerator environments. Measurements for fast neutron fluxes were completely negative under even the most likely conditions with a 6 MeV medical linac. Measurable fluxes of thermal and epithermal neutrons were obtained. However, in typical cases the amount of isomeric activation due to “slow” neutrons was 1% of the total activation and 6% in the worst case based on measured fluxes and known values of cross sections. This revised version was published online in August 2006 with corrections to the Cover Date.     

A note on levene's tests for equality of variances

Consider testing for equality variances in a one-way analysis of variance. Levene's test is the usual F-test for equality of means computed on psuedo-observations, which one defines as the absolute deviations of the data points from an estimate of the group ‘center’. We show that, asymptotically, Levene's test has the correct level whenever the estimate of group ‘center’ is an estimate of group median. This explains why published Monte-Carlo studies have found that Levene's original proposal of centering at the sample mean has the correct level only for symmetric distributions, while centering at the sample median has correct level even for asymmetric distributions. Generalizations are discussed.     

Shock initiated ignition in COS?O2?Ar mixtures

The ignition of COS + O₂ mixtures diluted in argon was studied behind reflected shocks in a single-pulse shock tube over the temperature range of 1100–1700°K. Ignition delay times and the distribution of reaction products before and after ignition were determined experimentally. From a total of 63 tests run at varying initial conditions, the following correlation for the induction times was derived: where β₁ = +0.30, β₂ = 1.12, and E = 16.9 kcal/mole. Using a reaction scheme of 14 steps, the following values were obtained by a computer modeling of the induction times: β₁ = +0.22, β₂ = 1.55, and E = 17.3 kcal/mole. The calculations showed that the reaction COS + S → CO + S₂ caused the inhibiting effect of the COS. The reaction COS → O ± CO₂ + S has a very strong accelerating effect, whereas the parallel channel COS + O → CO + SO shows the opposite effect. It was also shown that the reaction O + S₂ → SO + O is very slow and does not contribute to the overall oxidation reaction. It is suggested that the rate constant given to the four-center reaction COS + SO → CO₂ + S₂, that is, 10¹¹ cm³/mole · sec at 300°K is incorrect. This constant is not much higher than 10⁸ cm³/mole · sec at 1300°K.