A reconfigurable CPW bow-tie antenna using an integrated ferroelectric thin film varactor

A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna consists of a bowtie structure patch radiating element in the inner space of an annulus that is on a nongrounded substrate with a ferroelectric (FE) Barium Strontium Titanate (BST) thin film. The bowtie patch is fed by a coplanar waveguide (CPW) transmission line that also includes a CPW-based BST shunt varactor. Reconfiguration of the compact 8 mm × 8 mm system has been demonstrated by shifting the antenna system’s operating frequency 500 MHz in the 7–9 GHz band by applying a DC voltage bias

Perception of nonnative tonal contrasts by Mandarin-English and English-Mandarin sequential bilinguals

This study examined the role of acquisition order and crosslinguistic similarity in influencing transfer at the initial stage of perceptually acquiring a tonal third language (L3). Perception of tones in Yoruba and Thai was tested in adult sequential bilinguals representing three different first (L1) and second language (L2) backgrounds: L1 Mandarin-L2 English (MEBs), L1 English-L2 Mandarin (EMBs), and L1 English-L2 intonational/non-tonal (EIBs). MEBs outperformed EMBs and EIBs in discriminating L3 tonal contrasts in both languages, while EMBs showed a small advantage over EIBs on Yoruba. All groups showed better overall discrimination in Thai than Yoruba, but group differences were more robust in Yoruba. MEBs’ and EMBs’ poor discrimination of certain L3 contrasts was further reflected in the L3 tones being perceived as similar to the same Mandarin tone; however, EIBs, with no knowledge of Mandarin, showed many of the same similarity judgments. These findings thus suggest that L1 tonal experience has a particularly facilitative effect in L3 tone perception, but there is also a facilitative effect of L2 tonal experience. Further, crosslinguistic perceptual similarity between L1/L2 and L3 tones, as well as acoustic similarity between different L3 tones, play a significant role at this early stage of L3 tone acquisition.Published versio

Directional asymmetries reveal a universal bias in adult vowel perception

published online 21 April 2017Research on cross-language vowel perception in both infants and adults has shown that for many vowel contrasts, discrimination is easier when the same pair of vowels is presented in one direction compared to the reverse direction. According to one account, these directional asymmetries reflect a universal bias favoring “focal” vowels (i.e., vowels whose adjacent formants are close in frequency, which concentrates acoustic energy into a narrower spectral region). An alternative, but not mutually exclusive, account is that such effects reflect an experience-dependent bias favoring prototypical instances of native-language vowel categories. To disentangle the effects of focalization and prototypicality, the authors first identified a certain location in phonetic space where vowels were consistently categorized as /u/ by both Canadian-English and Canadian-French listeners, but that nevertheless varied in their stimulus goodness (i.e., the best Canadian-French /u/ exemplars were more focal compared to the best Canadian-English /u/ exemplars). In subsequent AX discrimination tests, both Canadian-English and Canadian-French listeners performed better at discriminating changes from less to more focal /u/’s compared to the reverse, regardless of variation in prototypicality. These findings demonstrate a universal bias favoring vowels with greater formant convergence that operates independently of biases related to language-specific prototype categorization.This research was supported by NSERC Discovery Grant No. 105397 to L.P. and NSERC Discovery Grant No. 312395 to L.M

Anomalous Behavior Of The Complex Conductivity Of Y_{1-x}Pr_xBa_2Cu_3O_7 Observed With THz Spectroscopy

We have measured the electrodynamic properties of Y_{1-x}Pr_xBa_2Cu_3O_7 single crystal thin films as a function of temperature using coherent THz-time-domain spectroscopy. We obtain directly the complex conductivity $\sigma=\sigma_1+i\sigma_2$, the London penetration depth $\lambda_L$, the plasma frequency $\omega_p$, and the quasiparticle scattering rate $1/\tau$. We find that $1/\tau$ drops exponentially rapidly with $T$ below the critical temperature in {\em all} the superconducting samples, implying that this behavior is a {\em signature} of high-$T_c$ superconductivity. The plasma frequency decreases with increasing Pr content, providing evidence that Pr depletes carriers, leaving the CuO planes {\em underdoped}. Both the conductivity in the THz region and the dc resistivity yield evidence for the opening of a spin gap {\em above} $T_c$.Comment: 9 pages, REVTEX 3.

Classical wave experiments on chaotic scattering

We review recent research on the transport properties of classical waves through chaotic systems with special emphasis on microwaves and sound waves. Inasmuch as these experiments use antennas or transducers to couple waves into or out of the systems, scattering theory has to be applied for a quantitative interpretation of the measurements. Most experiments concentrate on tests of predictions from random matrix theory and the random plane wave approximation. In all studied examples a quantitative agreement between experiment and theory is achieved. To this end it is necessary, however, to take absorption and imperfect coupling into account, concepts that were ignored in most previous theoretical investigations. Classical phase space signatures of scattering are being examined in a small number of experiments.Comment: 33 pages, 13 figures; invited review for the Special Issue of J. Phys. A: Math. Gen. on "Trends in Quantum Chaotic Scattering

Differential cross sections for pion charge exchange on the proton at 27.5 MeV

We have measured pion single charge exchange differential cross sections on the proton at 27.5 MeV incident $\pi^-$ kinetic energy in the center of momentum angular range between $0^\circ$ and $55^\circ$. The extracted cross sections are compared with predictions of the standard pion-nucleon partial wave analysis and found to be in excellent agreement.Comment: ReVTeX v3.0 with aps.sty, 23 pages in e-print format, 7 PostScript Figures and 4 Tables, also available via anonymous ftp at ftp://helena.phys.virginia.edu/pub/preprints/scx.p

Food mechanical properties and isotopic signatures in forest versus savannah dwelling eastern chimpanzees

Chimpanzees are traditionally described as ripe fruit specialists with large incisors but relatively small postcanine teeth, adhering to a somewhat narrow dietary niche. Field observations and isotopic analyses suggest that environmental conditions greatly affect habitat resource utilization by chimpanzee populations. Here we combine measures of dietary mechanics with stable isotope signatures from eastern chimpanzees living in tropical forest (Ngogo, Uganda) and savannah woodland (Issa Valley, Tanzania). We show that foods at Issa can present a considerable mechanical challenge, most saliently in the external tissues of savannah woodland plants compared to their tropical forest equivalents. This pattern is concurrent with different isotopic signatures between sites. These findings demonstrate that chimpanzee foods in some habitats are mechanically more demanding than previously thought, elucidating the broader evolutionary constraints acting on chimpanzee dental morphology. Similarly, these data can help clarify the dietary mechanical landscape of extinct hominins often overlooked by broad C3/C4 isotopic categories

Mobility Edge in Aperiodic Kronig-Penney Potentials with Correlated Disorder: Perturbative Approach

It is shown that a non-periodic Kronig-Penney model exhibits mobility edges if the positions of the scatterers are correlated at long distances. An analytical expression for the energy-dependent localization length is derived for weak disorder in terms of the real-space correlators defining the structural disorder in these systems. We also present an algorithm to construct a non-periodic but correlated sequence exhibiting desired mobility edges. This result could be used to construct window filters in electronic, acoustic, or photonic non-periodic structures.Comment: RevTex, 4 pages including 2 Postscript figure

Willing and able: action-state orientation and the relation between procedural justice and employee cooperation

Existing justice theory explains why fair procedures motivate employees to adopt cooperative goals, but it fails to explain how employees strive towards these goals. We study self-regulatory abilities that underlie goal striving; abilities that should thus affect employees’ display of cooperative behavior in response to procedural justice. Building on action control theory, we argue that employees who display effective self-regulatory strategies (action oriented employees) display relatively strong cooperative behavioral responses to fair procedures. A multisource field study and a laboratory experiment support this prediction. A subsequent experiment addresses the process underlying this effect by explicitly showing that action orientation facilitates attainment of the cooperative goals that people adopt in response to fair procedures, thus facilitating the display of actual cooperative behavior. This goal striving approach better integrates research on the relationship between procedural justice and employee cooperation in the self-regulation and the work motivation literature. It also offers organizations a new perspective on making procedural justice effective in stimulating employee cooperation by suggesting factors that help employees reach their adopted goals

Statistics of Resonances and Delay Times in Random Media: Beyond Random Matrix Theory

We review recent developments on quantum scattering from mesoscopic systems. Various spatial geometries whose closed analogs shows diffusive, localized or critical behavior are considered. These are features that cannot be described by the universal Random Matrix Theory results. Instead one has to go beyond this approximation and incorporate them in a non-perturbative way. Here, we pay particular emphasis to the traces of these non-universal characteristics, in the distribution of the Wigner delay times and resonance widths. The former quantity captures time dependent aspects of quantum scattering while the latter is associated with the poles of the scattering matrix.Comment: 30 pages, 15 figures (submitted to Journal of Phys. A: Math. and General, special issue on "Aspects of Quantum Chaotic Scattering"