Terahertz Quantum Cascade Laser With Efficient Coupling and Beam Profile

Quantum cascade lasers (QCLs) are unipolar semiconductor lasers, where the wavelength of emitted radiation is determined by the engineering of quantum states within the conduction band in coupled multiple-quantum-well heterostructures to have the desired energy separation. The recent development of terahertz QCLs has provided a new generation of solid-state sources for radiation in the terahertz frequency range. Terahertz QCLs have been demonstrated from 0.84 to 5.0 THz both in pulsed mode and continuous wave mode (CW mode). The approach employs a resonant-phonon depopulation concept. The metal-metal (MM) waveguide fabrication is performed using Cu-Cu thermo-compression bonding to bond the GaAs/AlGaAs epitaxial layer to a GaAs receptor wafer

Go viral or go broadcast? Characterizing the virality and growth of cascades

Quantifying the virality of cascades is an important question across disciplines such as the transmission of disease, the spread of information and the diffusion of innovations. An appropriate virality metric should be able to disambiguate between a shallow, broadcast-like diffusion process and a deep, multi-generational branching process. Although several valuable works have been dedicated to this field, most of them fail to take the position of the diffusion source into consideration, which makes them fall into the trap of graph isomorphism and would result in imprecise estimation of cascade virality inevitably under certain circumstances. In this paper, we propose a root-aware approach to quantifying the virality of cascades with proper consideration of the root node in a diffusion tree. With applications on synthetic and empirical cascades, we show the properties and potential utility of the proposed virality measure. Based on preferential attachment mechanisms, we further introduce a model to mimic the growth of cascades. The proposed model enables the interpolation between broadcast and viral spreading during the growth of cascades. Through numerical simulations, we demonstrate the effectiveness of the proposed model in characterizing the virality of growing cascades. Our work contributes to the understanding of cascade virality and growth, and could offer practical implications in a range of policy domains including viral marketing, infectious disease and information diffusion.Comment: 10 pages, 15 figures, 1 tabl

Divergent Effects of PERK and IRE1 Signaling on Cell Viability

Protein misfolding in the endoplasmic reticulum (ER) activates a set of intracellular signaling pathways, collectively termed the Unfolded Protein Response (UPR). UPR signaling promotes cell survival by reducing misfolded protein levels. If homeostasis cannot be restored, UPR signaling promotes cell death. The molecular basis for the switch between prosurvival and proapoptotic UPR function is poorly understood. The ER-resident proteins, PERK and IRE1, control two key UPR signaling pathways. Protein misfolding concomitantly activates PERK and IRE1 and has clouded insight into their contributions toward life or death cell fates. Here, we employed chemical-genetic strategies to activate individually PERK or IRE1 uncoupled from protein misfolding. We found that sustained PERK signaling impaired cell proliferation and promoted apoptosis. By contrast, equivalent durations of IRE1 signaling enhanced cell proliferation without promoting cell death. These results demonstrate that extended PERK and IRE1 signaling have opposite effects on cell viability. Differential activation of PERK and IRE1 may determine life or death decisions after ER protein misfolding

Universality of preference behaviors in online music-listener bipartite networks: A Big Data analysis

We investigate the formation of musical preferences of millions of users of the NetEase Cloud Music (NCM), one of the largest online music platforms in China. We combine the methods from complex networks theory and information sciences within the context of Big Data analysis to unveil statistical patterns and community structures underlying the formation and evolution of musical preference behaviors. Our analyses address the decay patterns of music influence, users' sensitivity to music, age and gender differences, and their relationship to regional economic indicators. Employing community detection in user-music bipartite networks, we identified eight major cultural communities in the population of NCM users. Female users exhibited higher within-group variability in preference behavior than males, with a major transition occurring around the age of 25. Moreveor, the musical tastes and the preference diversity measures of women were also more strongly associated with economic factors. However, in spite of the highly variable popularity of music tracks and the identified cultural and demographic differences, we observed that the evolution of musical preferences over time followed a power-law-like decaying function, and that NCM listeners showed the highest sensitivity to music released in their adolescence, peaking at the age of 13. Our findings suggest the existence of universal properties in the formation of musical tastes but also their culture-specific relationship to demographic factors, with wide-ranging implications for community detection and recommendation system design in online music platforms.Comment: 23 pages, 15 Figures, 4 Table

Reticular pseudodrusen in late-onset retinal degeneration

PURPOSE: To characterize the association of reticular pseudodrusen (RPD) with late-onset retinal degeneration (L-ORD) using multimodal imaging. DESIGN: Prospective, two-center, longitudinal case series. SUBJECTS: Twenty-nine cases with L-ORD. METHODS: All subjects were evaluated within a three-year interval with near-infrared reflectance, fundus autofluorescence, and spectral-domain optical coherence tomography. In addition, a subset of patients also underwent indocyanine green angiography, fundus fluorescein angiography, mesopic microperimetry, and multifocal electroretinography. Main outcome measures: Prevalence, topographic distribution, and temporal phenotypic changes of RPD in L-ORD. RESULTS: A total of 29 molecularly confirmed L-ORD cases were included in this prospective study. RPD was detected in 18 cases (62%) at baseline, of which 10 were male. The prevalence of RPD varied with age. The mean age of RPD patients was 57.3±7.2 years. RPD was not seen in cases below the fifth decade (n=3 patients) or in the eighth decade (n=5 patients). RPD were found commonly in the macula with relative sparing of the fovea and were also identified in the peripheral retina. The morphology of RPD changed with follow-up. Two cases (3 eyes) demonstrated RPD regression. CONCLUSIONS: RPD is found frequently in cases with L-ORD and at a younger age than in individuals with AMD. RPD exhibits quick formation and collapse, change in type and morphology with time, relative foveal-sparing, and also has a peripheral retinal location in L-ORD

Anharmonicity-induced isostructural phase transition of Zirconium under pressure

We have performed a detailed x-ray diffraction structural study of Zr under pressure and unambiguously identify the existence of a first-order isostructural bcc-to-bcc phase transition near 58 GPa. First-principles quantum molecular dynamics lattice dynamics calculations support the existence of this phase transition, in excellent agreement with experimental results, triggered by anharmonic effects. Our results highlight the potential ubiquity of anharmonically driven isostructural transitions within the periodic table under pressure and calls for follow-up experimental and theoretical studies

Speckle Space-Time Covariance in High-Contrast Imaging

We introduce a new framework for point-spread function (PSF) subtraction based on the spatio-temporal variation of speckle noise in high-contrast imaging data where the sampling timescale is faster than the speckle evolution timescale. One way that space-time covariance arises in the pupil is as atmospheric layers translate across the telescope aperture and create small, time-varying perturbations in the phase of the incoming wavefront. The propagation of this field to the focal plane preserves some of that space-time covariance. To utilize this covariance, our new approach uses a Karhunen-Lo\'eve transform on an image sequence, as opposed to a set of single reference images as in previous applications of Karhunen-Lo\'eve Image Processing (KLIP) for high-contrast imaging. With the recent development of photon-counting detectors, such as microwave kinetic inductance detectors (MKIDs), this technique now has the potential to improve contrast when used as a post-processing step. Preliminary testing on simulated data shows this technique can improve contrast by at least 10-20% from the original image, with significant potential for further improvement. For certain choices of parameters, this algorithm may provide larger contrast gains than spatial-only KLIP.Comment: Accepted to A