Recombination fluorescence in ultracold neutral plasmas

We present the first measurements and simulations of recombination fluorescence in ultracold neutral plasmas. In contrast with previous work, experiment and simulation are in significant disagreement. Comparison with a recombination model suggests that the disagreement could be due to the high energy portion of the electron energy distribution or to large energy changes in electron/Rydberg scattering. Recombination fluorescence opens a new diagnostic window in ultracold plasmas because it probes the deeply-bound Rydberg levels, which depend critically on electron energetics

Control system maintains selected liquid level

Single-sensor control system maintains liquid hydrogen at a preselected desired level within a tank, regardless of boiloff. It calibrates output in percentage. Thus, when the fuel is at the desired level, the system output will indicate 100 percent regardless of what percent of tank capacity the fuel has reached

Infants’ perception of rhythmic patterns

We explored 9-month-old infants perception of auditory temporal sequences in a series of three experiments. In Experiment 1, we presented some infants with tone sequences that were expected to induce a strongly metric framework and others with a sequence that was expected to induce a weakly metric framework or no such framework. Infants detected a change in the context of the former sequences but not in the latter sequence. In Experiment 2, infants listened to a tone sequence with temporal cues to duple or triple meter. Infants detected a change in the pattern with duple meter but not in the pattern with triple meter. In Experiment 3, infants listened to a tone sequence with harmonic cues to duple or triple meter. As in Experiment 2, infants detected a change in the context of the duple meter pattern but not in the context of triple meter. These findings are consistent with processing predispositions for auditory temporal sequences that induce a metric framework, particularly those in duple meter

Effects of deafness on acoustic characteristics of American English tense/lax vowels in maternal speech to infants

Recent studies have demonstrated that mothers exaggerate phonetic properties of infant-directed (ID) speech. However, these studies focused on a single acoustic dimension (frequency), whereas speech sounds are composed of multiple acoustic cues. Moreover, little is known about how mothers adjust phonetic properties of speech to children with hearing loss. This study examined mothers’ production of frequency and duration cues to the American English tense/lax vowel contrast in speech to profoundly deaf (N = 14) and normal-hearing (N = 14) infants, and to an adult experimenter. First and second formant frequencies and vowel duration of tense (/i/, /u/) and lax (/I/, /ʊ/) vowels were measured. Results demonstrated that for both infant groups mothers hyperarticulated the acoustic vowelspace and increased vowel duration in ID speech relative to adult-directed speech. Mean F2 values were decreased for the /u/ vowel and increased for the /I/ vowel, and vowelduration was longer for the /i/, /u/, and /I/ vowels in ID speech. However, neither acoustic cue differed in speech to hearing-impaired or normal-hearing infants. These results suggest that both formant frequencies and vowel duration that differentiate American English tense/lx vowel contrasts are modified in ID speech regardless of the hearing status of the addressee

Effects of simultaneous speech and sign on infants’ attention to spoken language

Objectives: To examine the hypothesis that infants receiving a degraded auditory signal have more difficulty segmenting words from fluent speech if familiarized with the words presented in both speech and sign compared to familiarization with the words presented in speech only. Study Design: Experiment utilizing an infant-controlled visual preference procedure. Methods: Twenty 8.5-month-old normal-hearing infants completed testing. Infants were familiarized with repetitions of words in either the speech + sign (n = 10) or the speech only (n = 10) condition. Results: Infants were then presented with four six-sentence passages using an infant-controlled visual preference procedure. Every sentence in two of the passages contained the words presented in the familiarization phase, whereas none of the sentences in the other two passages contained familiar words.Infants exposed to the speech + sign condition looked at familiar word passages for 15.3 seconds and at nonfamiliar word passages for 15.6 seconds, t (9) = -0.130, p = .45. Infants exposed to the speech only condition looked at familiar word passages for 20.9 seconds and to nonfamiliar word passages for 15.9 seconds. This difference was statistically significant, t (9) = 2.076, p = .03. Conclusions: Infants\u27 ability to segment words from degraded speech is negatively affected when these words are initially presented in simultaneous speech and sign. The current study suggests that a decreased ability to segment words from fluent speech may contribute towards the poorer performance of pediatric cochlear implant recipients in total communication settings on a wide range of spoken language outcome measures

Measurement and simulation of laser-induced fluorescence from non-equilibrium ultracold neutral plasmas

We report new measurements and simulations of laser-induced fluorescence in ultracold neutral plasmas. We focus on the earliest times, when the plasma equilibrium is evolving and before the plasma expands. In the simulation, the ions interact via the Yukawa potential in a small cell with wrapped boundary conditions. We solve the optical Bloch equation for each ion in the simulation as a function of time. Both the simulation and experiment show the initial Bloch vector rotation, disorder-induced heating, and coherent oscillation of the rms ion velocity. Detailed modeling of the fluorescence signal makes it possible to use fluorescence spectroscopy to probe ion dynamics in ultracold and strongly coupled plasmas

Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-alpha system at z_abs~2 toward Q 0551-366

We report the detection of H_2, CI, CI*, CI** and Cl I lines in a near Solar-metallicity ([Zn/H]=-0.13) damped Lyman-alpha (DLA) system at z_abs=1.962 observed on the line of sight to the quasar Q 0551-366. The iron-peak elements, X=Fe, Cr and Mn are depleted compared to zinc, [X/Zn] -0.8, probably because they are tied up onto dust grains. Among the three detected H_2-bearing clouds, spanning 55 km s^-1 in velocity space, we derive a total molecular hydrogen column density N(H_2)=2.6x10^17 cm^-2 and a mean molecular fraction f=2N(H_2)/(2N(H_2)+N(HI))=1.7x10^-3. The depletion of heavy elements (S, Si, Mg, Mn, Cr, Fe, Ni and Ti) in the central component is similar to that observed in the diffuse neutral gas of the Galactic halo. This depletion is approximately the same in the six CI-detected components independently of the presence or absence of H_2. The gas clouds in which H_2 is detected always have large densities, n_H>30 cm^-3, and low temperatures, T_01<~100 K. This shows that presence of dust, high particle density and/or low temperature are required for molecules to be present. The photo-dissociation rate derived in the components where H_2 is detected suggests the existence of a local UV radiation field similar in strength to the one in the Galaxy. Star formation therefore probably occurs near these H_2-bearing clouds.Comment: 9 pages, 7 figures, to appear in A&A; added reference in Sect.

Measurement and simulation of laser-induced fluorescence from non-equilibrium ultracold neutral plasmas

We report new measurements and simulations of laser-induced fluorescence in ultracold neutral plasmas. We focus on the earliest times, when the plasma equilibrium is evolving and before the plasma expands. In the simulation, the ions interact via the Yukawa potential in a small cell with wrapped boundary conditions. We solve the optical Bloch equation for each ion in the simulation as a function of time. Both the simulation and experiment show the initial Bloch vector rotation, disorder-induced heating, and coherent oscillation of the rms ion velocity. Detailed modeling of the fluorescence signal makes it possible to use fluorescence spectroscopy to probe ion dynamics in ultracold and strongly coupled plasmas