94 research outputs found
Chip-Based Laser with 1 Hertz Integrated Linewidth
Lasers with hertz-level linewidths on timescales up to seconds are critical
for precision metrology, timekeeping, and manipulation of quantum systems. Such
frequency stability typically relies on bulk-optic lasers and reference
cavities, where increased size is leveraged to improve noise performance, but
with the trade-off of cost, hand assembly, and limited application
environments. On the other hand, planar waveguide lasers and cavities exploit
the benefits of CMOS scalability but are fundamentally limited from achieving
hertz-level linewidths at longer times by stochastic noise and thermal
sensitivity inherent to the waveguide medium. These physical limits have
inhibited the development of compact laser systems with frequency noise
required for portable optical clocks that have performance well beyond
conventional microwave counterparts. In this work, we break this paradigm to
demonstrate a compact, high-coherence laser system at 1548 nm with a 1 s
integrated linewidth of 1.1 Hz and fractional frequency instability less than
10 from 1 ms to 1 s. The frequency noise at 1 Hz offset is suppressed
by 11 orders of magnitude from that of the free-running diode laser down to the
cavity thermal noise limit near 1 Hz/Hz, decreasing to 10 Hz/Hz
at 4 kHz offset. This low noise performance leverages wafer-scale integrated
lasers together with an 8 mL vacuum-gap cavity that employs micro-fabricated
mirrors with sub-angstrom roughness to yield an optical of 11.8 billion.
Significantly, all the critical components are lithographically defined on
planar substrates and hold the potential for parallel high-volume
manufacturing. Consequently, this work provides an important advance towards
compact lasers with hertz-level linewidths for applications such as portable
optical clocks, low-noise RF photonic oscillators, and related communication
and navigation systems
Photonic chip-based low noise microwave oscillator
Numerous modern technologies are reliant on the low-phase noise and exquisite
timing stability of microwave signals. Substantial progress has been made in
the field of microwave photonics, whereby low noise microwave signals are
generated by the down-conversion of ultra-stable optical references using a
frequency comb. Such systems, however, are constructed with bulk or fiber
optics and are difficult to further reduce in size and power consumption. Our
work addresses this challenge by leveraging advances in integrated photonics to
demonstrate low-noise microwave generation via two-point optical frequency
division. Narrow linewidth self-injection locked integrated lasers are
stabilized to a miniature Fabry-P\'{e}rot cavity, and the frequency gap between
the lasers is divided with an efficient dark-soliton frequency comb. The
stabilized output of the microcomb is photodetected to produce a microwave
signal at 20 GHz with phase noise of -96 dBc/Hz at 100 Hz offset frequency that
decreases to -135 dBc/Hz at 10 kHz offset--values which are unprecedented for
an integrated photonic system. All photonic components can be heterogeneously
integrated on a single chip, providing a significant advance for the
application of photonics to high-precision navigation, communication and timing
systems
Copper Corrosion Inhibition and Adsorption Behavior of 3-Amino-1,2,4-triazole
Corrosion inhibition of copper in 3% NaCl Solution by 3-amino-1.2,4-triazole (ATA) was studied in relation to the concentration of the inhibitor using electrochemical (ac impedance and dc polarization) and surface enhanced Raman spectroscopy (SERS) techniques. The results indicated that ATA was a good corrosion inhibiter for copper in a 3% NaCl solution. The inhibition efficiency was 97.65% at an ATA concentration of 20 mg.L-1. Polarization curves showed that ATA behaved as a type of cathodical inhibitor in 3% NaCl solution. Adsorption of ATA followed Langmuir's adsorption isotherm and the adsorption mechanism was typical of chemisorption. SERS revealed that inhibition of copper corrosion was due to adsorption of ATA molecules on the surface of copper. SERS also confirmed that the adsorbed ATA molecules formed a complex with Cu+ which prevented the formation of copper chloride complexes, CuCl2
A reconsideration of the sugar sweetened beverage tax in a household production model
We study the impact of a hypothetical tax on sugar - sweetened beverages (SSBs) on the U.S. households\u2019
nutrients purchase, welfare change, and health benefit. Differently from the traditional approach, Food at Home
(FAH) is here defined as a \u201chome\u201d good instead of a market good and consumers\u2019 demands derived under the
assumption that households maximize utility subject to both a money and a time constraint. The model is
estimated by using an incomplete approximate Exact Affine Stone Index (EASI) demand system on a data set
built by merging the U.S. consumer expenditure and time use surveys. Results show that a SSB tax would be
much more effective in decreasing household nutrients purchase than it would appear by estimating a model
neglecting time costs in home food production, due to a lesser compensation of calories from increasing FAH
consumption. A tax-induced 38% increase in SSB price is predicted to decrease the per capita energy purchase by
41 kcal/da
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A novel Bruch's membrane-mimetic electrospun substrate scaffold for human retinal pigment epithelium cells.
Various artificial membranes have been used as scaffolds for retinal pigment epithelium cells (RPE) for monolayer reconstruction, however, long-term cell viability and functionality are still largely unknown. This study aimed to construct an ultrathin porous nanofibrous film to mimic Bruch's membrane, and in particular to investigate human RPE cell responses to the resultant substrates. An ultrathin porous nanofibrous membrane was fabricated by using regenerated wild Antheraea pernyi silk fibroin (RWSF), polycaprolactone (PCL) and gelatin (Gt) and displayed a thickness of 3-5 μm, with a high porosity and an average fiber diameter of 166 ± 85 nm. Human RPE cells seeded on the RWSF/PCL/Gt membranes showed a higher cell growth rate (p < 0.05), and a typical expression pattern of RPE signature genes, with reduced expression of inflammatory mediators. With long-term cultivation on the substrates, RPE cells exhibited characteristic polygonal morphology and development of apical microvilli. Immunocytochemisty demonstrated RPE-specific expression profiles in cells after 12-weeks of co-culture on RWSF/PCL/Gt membranes. Interestingly, the cells on the RWSF/PCL/Gt membranes functionally secreted polarized PEDF and phagocytosed labeled porcine POS. Furthermore, RWSF/PCL/Gt membranes transplanted subsclerally exhibited excellent biocompatibility without any evidence of inflammation or rejection. In conclusion, we established a novel RWSF-based substrate for growth of RPE cells with excellent cytocompatibility in vitro and biocompatibility in vivo for potential use as a prosthetic Bruch's membrane for RPE transplantation
Retrieving Doppler Frequency via Local Correlation Method of Segmented Modeling
The high accuracy radio Doppler frequency is critical for navigating a deep space probe and for planetary radio science experiments. In this paper, we propose a novel method based on the local correlation of segmented modeling to retrieve Doppler frequency by processing an open-loop radio link signal from one single ground station. Simulations are implemented, which prove the validity of this method. Mars Express (MEX) and Tianwen-1 observation experiments were carried out by Chinese Deep Space Stations (CDSS). X-band Doppler frequency observables were retrieved by the proposed method to participate in orbit determination. The results show that the accuracy of velocity residuals of orbit determination in open-loop mode is from 0.043 mm/s to 0.061 mm/s in 1 s integration; the average accuracy of Doppler frequency is about 3.3 mHz in 1 s integration and about 0.73 mHz in 60 s integration. The Doppler accuracy here is better than that of the digital baseband receiver at CDSS. The algorithm is efficient and flexible when the deep space probe is in a high dynamic mode and in low signal to noise ratio (SNR). This will benefit Chinese deep space exploration missions and planetary radio science experiments
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