Training the perception of Hindi dental and retroflex stops by native speakers of American English and Japanese

Perception of second language speech sounds is influenced by one's first language. For example, speakers of American English have difficulty perceiving dental versus retroflex stop consonants in Hindi although English has both dental and retroflex allophones of alveolar stops. Japanese, unlike English, has a contrast similar to Hindi, specifically, the Japanese /d/ versus the flapped /r/ which is sometimes produced as a retroflex. This study compared American and Japanese speakers' identification of the Hindi contrast in CV syllable contexts where C varied in voicing and aspiration. The study then evaluated the participants' increase in identifying the distinction after training with a computer-interactive program. Training sessions progressively increased in difficulty by decreasing the extent of vowel truncation in stimuli and by adding new speakers. Although all participants improved significantly, Japanese participants were more accurate than Americans in distinguishing the contrast on pretest, during training, and on posttest. Transfer was observed to three new consonantal contexts, a new vowel context, and a new speaker's productions. Some abstract aspect of the contrast was apparently learned during training. It is suggested that allophonic experience with dental and retroflex stops may be detrimental to perception of the new contrast.     

Chloride binding by a polyimidazolium macrocycle detected via fluorescence,NMR, and X-ray crystallography

Herein, we describe a macrocyclic polyimidazolium receptor that is preorganized for the binding of anionic guests, and particularly chloride. Additionally, diphenylimidazolium units were incorporated into this structure to enhance photophysical properties that were exploited for signal transduction of binding. In subsequent fluorescence binding studies, this receptor was found to bind a range of halides as well as phosphate with high affinity (K_a=1.8×10⁴, and 1.5×10⁴ for phosphate and chloride, respectively) in a competitive solvent mixture (1:1 water/acetonitrile). Results under these conditions were fitted to 1:1 binding curves, and indicated modest selectivity of the host for phosphate and chloride over other halides. Binding studies were also performed using ¹H NMR spectroscopy, during which the imidazolium C–H signal was observed to shift downfield upon titration with anions. These experiments were run in less polar solvent (1:9 water/acetonitrile), and could not be fitted to a 1:1 binding curve, suggesting higher order aggregates in this environment. Binding was further probed in the solid state by obtaining an X-ray crystal structure of receptor–iodide complex. In the resulting structure, two iodides were found to bind through interactions with two polyimidazolium hydrogens each. These results show that the described macrocycle is effective for anion-binding in competitive solvent, with modest selectivity for chloride over other halides, and that the nature of the binding interactions varies depending upon the solvent environment.     

A plane layered model to estimate in situ ultrasound exposures

Determination of in situ ultrasound exposures in experimental animals and patients is necessary to assess any potential hazard of ultrasound implied by reported biological effects in animals. A layered model was used to calculate total attenuation of ultrasound pulses as they passed through tissue layers to an organ site, thus enabling calculation of in situ intensities from free-field transducer emissions. The model assumes plane homogeneous layers of tissue of known thickness, attenuation and acoustic impedance. Calculations based on the model, compared with in situ measurements in a human cadaver specimen, were accurate to within approximately +/- 3 dB. We then calculated in situ clinical exposures using published obstetric B-scans. Total attenuation to the fetus averaged approximately 11 dB at 3.5 MHz.     

Resolved line profiles of atomic oxygen resonance lamps used in the upper atmosphere

Line profiles of the 130-nm OI(³P-³S) resonance triplet emitted by r.f. excited helium/ oxygen lamps have been resolved using a photoelectric echelle spectrometer. These profiles have been reproduced using a self-absorbed double-Gaussian spectral distribution in which the relative amplitudes of the Gaussian components are functions of the oxygen and helium partial pressures in the lamps. Reasons for the form of the observed spectral distribution are suggested and the importance of the spectrometer measurements to studies of atomic oxygen in the upper atmosphere involving this type of lamp illustrated.     

Evidence for anchimeric assistance in the expulsion of bromine from ring-substituted β-phenylethyl bromides: When is a simple cleavage a rearrangement?

Using the principles of the quasi-equilibrium theory, substituent effects, deuterium labeling and comparison of compound behavior, we provide strong evidence for aryl participation in the expalsion of Br· from the molecular ion of β-phenylethyl bromide and eleven of its ringsubstitued derivatives. This reaction shows a kinetic behavior which is typical of rearrangements, its activation energy is lower than that of similar reactions where participation is partially or completely precluded and substitute effects are not only consistent with a particular process, but are also consistent with those predicted from solution chemistry.     

Off-axis line profiles of atomic-oxygen resonance lamps used in the upper atmosphere

Line profiles of the 130-nm OI (³P-³S) resonance triplet emitted in an off-axis direction by radio-frequency excited helium/oxygen lamps have been investigated using a line-absorption technique. The lamps concerned are of a type widely used in studies of the upper-atmospheric atomic-oxygen distribution. Resonance radiation emitted off-axis by these lamps is found to be more strong absorbed by $\text{O(}{}^3\text{P)}$ than that emitted on-axis, in a manner consistent with (a) a self-absorbed double-Gaussian spectral distribution model developed previously and (b) simple geometric considerations. Attention is drawn to potential difficulties in the interpretation of upper-atmospheric atomic-oxygen measurements if an appreciable amount of off-axis radiation from these lamps is employed.     

Convergence of the bertaut series and the calculation of the electrostatic energy of an extended crystalline lattice

Computations are reported which enable the prediction of the necessary truncation of the Bertaut series for various charge density functions consistent with various degrees of convergence. The results are sufficiently extensive to be applicable to almost all lattices.     

The centenary of powered flight: The next 100 years

Experimental Techniques -     

A Systems Approach to Management

A procedure is outlined for deciding the mix of price and variable non-price features, such as quality, delivery, service or financing, to be included in a bid. The level of each non-price feature is set independently by comparing incremental spending against the alternative price reduction and basing the choice on value to the faction in the customer organization expected to dominate in the choice of the successful bid. Divergence from competition on all non-price features, both fixed and variable, is then taken into account in setting price by calculating a net price equivalent of feature differences as against each competitor. For any given markup the probability of success against a competitor over whom there is a net advantage is the same as that for an equivalently lower markup were price to be the sole basis for allocating the order.