The effect of perceived speaker age on the perception of PIN and PEN vowels in Houston, Texas

In a study of native listeners\u27 implicit knowledge of the social distribution of a phonological variable we found that the perceived distribution does not completely match the findings of production surveys of the same variable in the same community. This presents an interesting challenge to models of linguistic variation based exclusively on production data, and questions how the distribution of sociolinguistic variables is best defined. The linguistic phenomenon we are investigating is the \u27unmerger\u27 of pre-nasal /i/ and /e/ among Anglo Houstonians. This long-standing feature of Southern American English is increasingly losing ground in large metropolitan centers of the South (e.g. Tillery and Bailey 2004). We conducted a speech perception experiment to measure the degree to which Houstonians expect Anglo speakers of three different age groups to participate in the merger. The experiment was conducted using a head-mounted eye-tracker, which monitored the participants\u27 eye movements as they selected on a computer screen the lexical items which they heard (Tanenhaus et al. 2000). Of particular interest were participants\u27 eye fixations on /eN/ and /iN/ competitors, i.e. words which are temporarily ambiguous with the target word in a merged production system. We interpret a greater amount of looks to the competitor as an indicator of the listener\u27s readiness to assume that the speaker may have a merged system. The results show that, as predicted, listeners are more likely to assume a merged system when listening to an old speaker than when listening to a middle-aged speaker. However, we find no significant difference between the perception of a middle-aged and a young speaker. These results generally corroborate our recent production surveys in Houston (Gentry 2006; Pantos 2006), which show the merger to be positively correlated with age. However, there is a discrepancy between our participants’ perception and the actual production of Houstonians in the middle-aged group. Although, in production terms, native Houstonians in this group pattern with old speakers in participating in the merger, listeners expect a middle-aged speaker to pattern with a young speaker in being less merged. We suggest that this mismatch is due to recent demographic changes in Houston, with large numbers of non-Southern Anglo speakers moving into the Houston metropolitan area in the course of the Sunbelt migration (Thomas 1997; Klineberg 2006). Native listeners who are exposed to this linguistically mixed population apparently associate merged vowels specifically only with the oldest speakers, even though some younger speakers are also merged. Our study adds to previous research on the perception of vowel merger, including near-merger (Di Paolo and Faber 1990, Labov et al. 1991, inter alia) by providing additional evidence for the role of perceived speaker dialect as a potentially disambiguating factor in speech perception (Hay et al. 2006). Our findings have broad implications for the study of language variation as they challenge sociolinguists to consider whether the variation we seek to describe resides in the “objective” production of speakers native to a community, or rather in the “subjective” experience of its native listeners

Influence of microscopic and macroscopic effects on attosecond pulse generation using two-color laser fields

Attosecond pulses and pulse trains generated by high-order harmonic generation are finding broad applications in advanced spectroscopies and imaging, enabling sub-femtosecond electron dynamics to be probed in atomic, molecular and material systems. To date, isolated attosecond pulses have been generated either by using very short few-cycle driving pulses, or by using temporal and polarization gating, or by taking advantage of phase-matching gating. Here we show that by driving high harmonics with a two-color linearly polarized laser field, the temporal window for time-gated phase matching is shorter than for the equivalent singe-color driving laser. As a result, we can generate quasi-isolated attosecond pulses with a peak width of ∼ 450 as using relatively long 26 femtosecond laser pulses. Our experimental data are in good agreement with theoretical simulations, and show that the phase matching window decreases by a factor of 4 - from four optical cycles in the case of a single-color fundamental driving laser, to one optical cycle in the case of two-color (ω-2ω) laser drivers. Finally, we also demonstrate that by changing the relative delay between the two-color laser fields, we can control the duration of the attosecond bursts from 450 as to 1.2 fs.National Science Foundation (NSF) (1125844); Air Force Office of Scientific Research (FA9550-16-1-0121); REA (328334); Junta de Castilla y León (SA046U16); MINECO (FIS2013-44174-P, FIS2016-75652-P)

Resolution of the type material of the Asian elephant, Elephas maximus Linnaeus, 1758 (Proboscidea, Elephantidae)

The understanding of Earth’s biodiversity depends critically on the accurate identification and nomenclature of species. Many species were described centuries ago, and in a surprising number of cases their nomenclature or type material remain unclear or inconsistent. A prime example is provided by Elephas maximus, one of the most iconic and well-known mammalian species, described and named by Linnaeus (1758) and today designating the Asian elephant. We used morphological, ancient DNA (aDNA), and high-throughput ancient proteomic analyses to demonstrate that a widely discussed syntype specimen of E. maximus, a complete foetus preserved in ethanol, is actually an African elephant, genus Loxodonta. We further discovered that an additional E. maximus syntype, mentioned in a description by John Ray (1693) cited by Linnaeus, has been preserved as an almost complete skeleton at the Natural History Museum of the University of Florence. Having confirmed its identity as an Asian elephant through both morphological and ancient DNA analyses, we designate this specimen as the lectotype of E. maximus

Bright, single helicity, high harmonics driven by mid-infrared bicircular laser fields

[EN]High-harmonic generation (HHG) is a unique tabletop light source with femtosecond-to-attosecond pulse duration and tailorable polarization and beam shape. Here, we use counter-rotating femtosecond laser pulses of 0.8 µm and 2.0 μm to extend the photon energy range of circularly polarized high-harmonics and also generate single-helicity HHG spectra. By driving HHG in helium, we produce circularly polarized soft x-ray harmonics beyond 170 eV—the highest photon energy of circularly polarized HHG achieved to date. In an Ar medium, dense spectra at photon energies well beyond the Cooper minimum are generated, with regions composed of a single helicity—consistent with the generation of a train of circularly polarized attosecond pulses. Finally, we show theoretically that circularly polarized HHG photon energies can extend beyond the carbon K edge, extending the range of molecular and materials systems that can be accessed using dynamic HHG chiral spectro-microscopiesDepartment of Energy BES (DE-FG02-99ER14982); Air Force Office of Scientific Research (FA9550-16-1-0121); National Science Foundation (DGE-1144083, DGE-1650115); European Research Council (8511201); Ministerio de Ciencia, Innovación y Universidades (PID2019-106910GB-100); Junta de Castilla y León (SA287P18); Ramón y Cajal contract (RYC-2017-22745)

Helicity-Selective Enhancement and Polarization Control of Attosecond High Harmonic Waveforms Driven by Bichromatic Circularly Polarized Laser Fields

source of bright, circularly polarized, extreme ultraviolet, and soft x-ray beams, where the individual harmonics themselves are completely circularly polarized. Here, we demonstrate the ability to preferentially select either the right or left circularly polarized harmonics simply by adjusting the relative intensity ratio of the bichromatic circularly polarized driving laser field. In the frequency domain, this significantly enhances the harmonic orders that rotate in the same direction as the higher-intensity driving laser. In the time domain, this helicity-dependent enhancement corresponds to control over the polarization of the resulting attosecond waveforms. This helicity control enables the generation of circularly polarized high harmonics with a user-defined polarization of the underlying attosecond bursts. In the future, this technique should allow for the production of bright highly elliptical harmonic supercontinua as well as the generation of isolated elliptically polarized attosecond pulses.H. K. and M. M. graciously acknowledge support from the Department of Energy BES Award No. DE-FG02- 99ER14982 for the experimental implementation, as well as a MURI grant from the Air Force Office of Scientific Research under Award No. FA9550-16-1-0121 for the theory. J. E. and C. M. acknowledge support from National Science Foundation Graduate Research Fellowships (Grant No. DGE-1144083). C. H.-G. acknowl- edges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007-2013), under REA Grant No. 328334, from Junta de Castilla y León (Project No. SA046U16) and Spanish Ministerio de Economía y Competitividad, MINECO (Projects No. FIS2013-44174-P and No. FIS2016-75652-P). Part of this work utilized the Janus supercomputer, which is sup- ported by the U.S. National Science Foundation (Grant No. CNS-0821794) and the University of Colorado Boulder

Phase matching of noncollinear sum and difference frequency high harmonic generation above and below the critical ionization level

We investigate the macroscopic physics of noncollinear high harmonic generation (HHG) at high pressures. We make the first experimental demonstration of phase matching of noncollinear high-order-difference-frequency generation at ionization fractions above the critical ionization level, which normally sets an upper limit on the achievable cutoff photon energies. Additionally, we show that noncollinear high-order-sum-frequency generation requires much higher pressures for phase matching than single-beam HHG does, which mitigates the short interaction region in this geometry. We also dramatically increase the experimentally realized cutoff energy of noncollinear circularly polarized HHG, reaching photon energies of 90 eV. Finally, we achieve complete angular separation of high harmonic orders without the use of a spectrometer.Department of Energy BES Award DE-FG02-99ER14982. MURI grant from the Air Force Office of Scientific Research under Award Number FA9550-16-1-0121. National Science Foundation Graduate Research Fellowship (DGE-1144083). Junta de Castilla y León (Project SA046U16) and Spanish MINECO (FIS2013-44174-P, FIS2016-75652-P)

Tomographic reconstruction of circularly polarized high-harmonic fields: 3D attosecond metrology

Bright, circularly polarized, extreme ultraviolet (EUV) and soft x-ray high-harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. Although the resulting circularly polarized harmonics consist of relatively simple pairs of peaks in the spectral domain, in the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency, and polarization. We extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with circularly polarized high-harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date.This work was done at JILA. We gratefully acknowledge support from the NSF through the Physics Frontiers Centers Program with grant no. PHY1125844 and the Gordon and Betty Moore Foundation EPiQS (Emergent Phenomena in Quantum Systems) Initiative through Grant GBMF4538 to M.M. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the European Union Seventh Framework Programme for Research and Technological Development (2007–2013), under Research Executive Agency grant agreement no. 328334. R.K. acknowledges the Swedish Research Council (VR) for financial support. A.J.-B. was supported by grants from the U.S. NSF (grant nos. PHY-1125844 and PHY-1068706). C.H.-G. and L.P. acknowledge support from Junta de Castilla y León (project SA116U13) and MINECO (Ministerio de Econom a y Competitividad) (FIS2013-44174-P and FIS2015-71933-REDT). This work used the Janus supercomputer, which is supported by the U.S. NSF (grant no. CNS-0821794) and the University of Colorado, Boulder. P.G. acknowledges support from the Deutsche Forschungsgemeinschaft (no. GR 4234/1-1)

Erratum: Non-collinear generation of angularly isolated circularly polarized high harmonics.

[EN]In the version of this Article originally published the blue dashed line was mislabelled in the legend in Fig. 3d and the label should have read i Evert. This has now been corrected in the online versions of the Article