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In this paper a novel optical vector network analyzer (OVNA) utilizing a distributed feedback semiconductor optical amplifier (DFB-SOA) is introduced. The proposed OVNA is implemented by converting the transmission response of the optical device under test (ODUT) into the electrical domain. The main principle of the OVNA is predicated on the optical carrier restoration facilitated by the wavelength-selective amplification attribute of the DFB-SOA. The implemented OVNA effectively determined the transmission spectrum of an optical filter possessing a passband of 9-GHz bandwidth, achieving a commendable resolution of 25 MHz in the measurement process. The dynamic range of the OVNA can be broadened by adjust the driven current under the DFB-SOA. Additionally, the detection range of our system can be expanded through the utilization of broadband optoelectronic devices. Furthermore, the OVNA possesses considerable potential for integration onto a single chip. [ABSTRACT FROM AUTHOR]

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

Slackwater deposits representing past flood events provide a robust means to extend systematic gage records further back in time, place historic floods in a longer-term context, and reduce uncertainties in flood hazard analysis. The identification and application of slackwater deposits in riverine paleoflood hydrology has traditionally been limited to arid bedrock-controlled environments and periglacial environments. In this study, we utilize methods developed in humid alluvial settings and apply them to slackwater deposits, one of the first studies to do so. This novel approach uses sediment texture and geochemistry to distinguish slackwater deposits from in situ material in a temperate alluvial setting. We identify multiple slackwater deposits in two rock shelters situated on bluffs adjacent to the lower Ohio River. Flood age estimates are based on optically stimulated luminescence (OSL) dating, and discharge estimates are based on a 1D HEC-RAS model. The uppermost slackwater deposit at both sites corresponds to the AD 1937 historic flood of record (∼31,400 m3/s), while another slackwater deposit identified only at the lower elevation site corresponds to a paleoflood that occurred around AD 1650 with a discharge of ∼23,900 m3/s. Our findings imply that the AD 1937 flood represents the largest magnitude flood on the lower Ohio River in at least the last 400 years. Inclusion of the paleoflood into a flood frequency analysis for the Ohio River at Louisville reduces uncertainties in large flood quantiles by ∼50%. [ABSTRACT FROM AUTHOR]

竞争战略在美国对外政策中占有重要地位，尤其在和主要对手的较量中，美国善于运用这一战略并曾收到较大成效，其中最显著的案例就是在美苏冷战中的充分运用。在美国学界和战略界的推动下，竞争战略理念在美对外战略中快速回归，也成为特朗普政府对华政策调整的重要理论依据。近来美国不断强化对华战略竞争与遏制的舆论动员，设置涉华议题，为强化对华战略竞争与遏制提供法律依据，并在等多个领域出手，全面强化对华战略竞争压力，甚至更多地利用台湾、香港局势的发展变化来牵制中国。面对咄咄逼人的竞争态势，中国既需抓住关键也需把握全局，既要坚守底线也要进退有据，有效管控中美竞争，化解战略压力拓展战略主动；而在竞争中更须切实提升国家治理能力和水平，筑牢战略竞争的国内基础，同时也要积极顺应世界变局，因势利导努力牵引中美关系的发展方向。 【关键词】战略竞争 中美关系 竞争管控 制衡能力 因势利导

Author(s): Samuel E. Munoz (corresponding author) [1, 2, 3]; Liviu Giosan [1]; Matthew D. Therrell [4]; Jonathan W. F. Remo [5]; Zhixiong Shen [6, 7]; Richard M. Sullivan [1, 8]; [...]