Actively Controlled Frequency-Agile Fano-Resonant Metasurface for Broadband and Unity Modulation

The active control to the local resonant mode of metasurface is a promising route for improving the operation bandwidth limitation of metasurface. Here, we propose and experimentally demonstrated the active tunabilities in a frequency-agile Fano-resonant metasurface. The metasurface with a pair of asymmetric split ring resonators is integrated with double varactor diodes for active control of the sharp Fano resonance. It is found that the sharp Fano-type spectrum appears due to the near-field interferences between the collective electric and magnetic dipole modes. The physical insight is revealed through local field analysis, multipole decomposition and temporal coupled-mode theory. It is also found that the metasurface can be employed as a broadband and unity modulator. Hopefully, our results could inspire sophisticated electrically controlled photonic devices with novel functions.

Uncertainty in tuning evaluation with low-register complex tones of orchestra instruments

The relationship between perceived pitch and harmonic spectrum in complex tones is ambiguous. In this study, 31 professional orchestra musicians participated in a listening experiment where they adjusted the pitch of complex low-register successively presented tones to unison. Tones ranged from A0 to A2 (27.6–110 Hz) and were derived from acoustic instrument samples at three different dynamic levels. Four orchestra instruments were chosen as sources of the stimuli; double bass, bass tuba, contrabassoon, and contrabass clarinet. In addition, a sawtooth tone with 13 harmonics was included as a synthetic reference stimulus. The deviation of subjects’ tuning adjustments from unison tuning was greatest for the lowest tones, but remained unexpectedly high also for higher tones, even though all participants had long experience in accurate tuning. Preceding studies have proposed spectral centroid and Terhardt’s virtual pitch theory as useful predictors of the influence of the envelope of a harmonic spectrum on the perceived pitch. However, neither of these concepts were supported by our results. According to the principal component analysis of spectral differences between the presented tone pairs, the contrabass clarinet-type spectrum, where every second harmonic is attenuated, lowered the perceived pitch of a tone compared with tones with the same fundamental frequency but a different spectral envelope. In summary, the pitches of the stimuli were perceived as undefined and highly dependent on the listener, spectrum, and dynamic level. Despite their high professional level, the subjects did not perceive a common, unambiguous pitch of any of the stimuli. The contrabass clarinet-type spectrum lowered the perceived pitch.

The influence of an interfacial hBN layer on the fluorescence of an organic molecule

We investigated the ability of a single layer of hexagonal boron nitride (hBN) to decouple the excited state of the organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) from the supporting Cu(111) surface by Raman and fluorescence (FL) spectroscopy. The Raman fingerprint-type spectrum of PTCDA served as a monitor for the presence of molecules on the surface. Several broad and weak FL lines between 18,150 and 18,450 cm−1 can be detected, already from the first monolayer onward. In contrast, FL from PTCDA on a bare Cu(111) surface is present only from the second PTCDA layer onward. Hence, a single layer of hBN decouples PTCDA from the metal substrate to an extent that a weak radiative FL decay of the optical excitation can occur. The different FL lines can be ascribed to different environments of the adsorption sites, namely molecules adsorbed at surface defects, in large ordered domains, and located in the second layer.

Asymmetrical nebula of the M33 variable GR290 (WR/LBV)

Context. GR 290 (M 33 V0532 = Romano’s star) is a luminous M 33 object undergoing photometric variability typical for luminous blue variable stars. It lies inside the Wolf-Rayet region in the Hertzsprung-Russell diagram and possesses a WN8-type spectrum at the light minima. Analysis of Gran Telescopio Canarias spectra obtained in 2016 led to the conclusion that it is surrounded by an unresolved H II region formed mostly of ejected material from the central star and revealed the presence of a second, more extended asymmetrical emission region. Aims. The aim of this paper is to further explore the structure of the nearby environment of GR 290. Methods. Long-slit spectra of GR 290 were obtained with three slit orientations in the visual and red spectral regions. The emission-line distribution for each slit was analyzed. Results. We confirm the presence of an asymmetric H II region that extends ~50 pc to the south; ~30 pc to the north, and southeast; ~20 pc to the east and northwest; and ~10 pc to the west. We also present the first spectrum to be acquired of a star belonging to the neighboring OB 88 association, J013501.87+304157.3, which we classify as a B-type supergiant with a possible binary companion.

A new and unusual LBV-like outburst from a Wolf–Rayet star in the outskirts of M33

ABSTRACT MCA-1B (also called UIT003) is a luminous hot star in the western outskirts of M33, classified over 20 yr ago with a spectral type of Ofpe/WN9 and identified then as a candidate luminous blue variable (LBV). Palomar Transient Factory data reveal that this star brightened in 2010, with a light curve resembling that of the classic LBV star AF And in M31. Other Ofpe/WN9 stars have erupted as LBVs, but MCA-1B was unusual because it remained hot. It showed a WN-type spectrum throughout its eruption, whereas LBVs usually get much cooler. MCA-1B showed an almost four-fold increase in bolometric luminosity and a doubling of its radius, but its temperature stayed ≳29 kK. As it faded, it shifted to even hotter temperatures, exhibiting a WN7/WN8-type spectrum, and doubling its wind speed. MCA-1B is reminiscent of some supernova impostors, and its location resembles the isolated environment of SN 2009ip. It is most similar to HD 5980 (in the Small Magellanic Cloud) and GR 290 (also in M33). Whereas these two LBVs exhibited B-type spectra in eruption, MCA-1B is the first clear case where a Wolf–Rayet (WR) spectrum persisted at all times. Together, MCA-1B, HD 5980, and GR 290 constitute a class of WN-type LBVs, distinct from S Doradus LBVs. They are most interesting in the context of LBVs at low metallicity, a possible post-LBV/WR transition in binaries, and as likely Type Ibn supernova progenitors.

Thermal neutron scattering data for liquid molten salt LiF-BeF2

Ab initio molecular dynamics (AIMD) methods were used to calculate the density of states (DOS) for liquid molten salt Li2BeF4 (LiF-BeF2) in different temperatures. The Egelstaff and Schofield effective width model was used to obtain the diffusion-type spectrum of the DOS and the corresponding partial s (α, β). Finally, the thermal neutron scattering data for liquid molten salt LiF-BeF2 were given.

TASK-SPECIFIC METACOGNITIVE ACCURACY DECLINES ACROSS THE DEMENTIA-ALZHEIMER’S TYPE SPECTRUM

Subjective cognitive complaints (SCCs) remain part of the diagnostic criteria for amnestic mild cognitive impairment (aMCI), the prodromal stage of dementia - Alzheimer’s type (DAT), despite weak relationships between self-reported and objectively-measured functioning. Most metacognitive measures focus on ratings of global retrospective memory rating only; greater subtlety in measurement of SCCs is required. Similarly, it is critical to identify the disease stage at which the clinical utility of SCCs is nullified by impaired insight. This study aims to evaluate group differences in (a) task-specific metacognitive ratings, and (b) the accuracy of these ratings in individuals diagnosed as cognitively intact (CI), with aMCI, or with DAT. 99 older adults (M-age = 69.43, SD-age = 6.98; M-edu = 15.54, SD-edu = 2.47; CI: n = 50, aMCI: n = 34, DAT: n = 15) enrolled in the University of Michigan Memory and Aging Project rated their performance on the Object Location Touchscreen Task (OLTT), an ecologically valid memory measure. One-way analysis of variance (ANOVA) revealed that individuals with aMCI-multiple domain or DAT rated their memory performance similarly to CI individuals, though the aMCI-single domain group rated themselves as more impaired. Bivariate Pearson’s r correlations demonstrated a decline in the strength of the relationship between task-specific metacognitive ratings and actual OLTT memory performance with increasing diagnostic severity. These findings suggest a decline in insight on task-specific memory ratings across the DAT spectrum, and call into question the use of self-reported SCCs as a diagnostic tool in later stages of disease progression.