Global stability of the open Milne spacetime

The open Milne cosmological spacetime has a 3-dimensional Cauchy surface isometric to the (non-compact) hyperbolic space. We prove the globally nonlinear stability of the open Milne spacetime for both massive and massless Einstein-scalar field equations and show that as time goes to infinity, the spatial metric tends to the hyperbolic metric. The proof is based on the Gaussian normal coordinates, in which the decay rates of gravity are determined by the expanding geometry of Milne spacetime.Comment: 36pages, Comments are welcom

Mid-IR Multiwavelength Difference Frequency Generation Based on Fiber Lasers

A mid-IR multiwavelength difference frequency generation (DFG) laser source with fiber laser fundamental lights is demonstrated by using the dispersion property of PPLN to broaden the quasi-phase-matching (QPM) acceptance bandwidth (BW). Our results show that the QPM BW for the pump YDFL is much larger than that for the signal EDFL. Using a multiwavelength YDFL and a single-wavelength EDFL as the pump and the signal lights, the DFG laser source can simultaneously emit 14 mid-IR wavelengths with the spacing of 14nm at a fixed PPLN temperature. Moreover, mid-IR multiwavelength lasing lines can be synchronously tuned between 3.28 and 3.47μm

Surface Measurement and Evaluation of Fiber Woven Composites

The surfaces of fiber woven composites (FWCs), especially woven ceramic matrix composites (WCMCs), are obviously anisotropic. Many kinds of damage, which are different from traditional homogeneous materials, could be caused by the fabrication and machining process. The old surface evaluation system appropriate for isotropic materials is no longer suitable to WCMCs, thus causing many difficulties in terms of their wide industrial applications. This chapter presents a grading surface measurement and evaluation system for WCMCs based on their microstructures. The system includes four levels: fiber, fiber bundle, cell body, and the whole surface. On the fiber level, the typical forms of fiber damage, and their effects on the surface morphology of WCMCs are analyzed, which lays a foundation for the measurement and evaluation methods on the next three levels. On each subsequent level, the system proposes a set of surface measurement sampling parameter determination methods and surface quality evaluation methods based on the principle of statistics. As demonstrations, the surface measurement and evaluation on each level were processed on a carbon fiber-reinforced silicon carbide matrix composite (Cf/SiC) to illustrate the methodology of the system

Synthesis, Optical Properties, and Photocatalytic Activity of One-Dimensional CdS@ZnS Core-Shell Nanocomposites

One-dimensional (1D) CdS@ZnS core-shell nanocomposites were successfully synthesized via a two-step solvothermal method. Preformed CdS nanowires with a diameter of ca. 45 nm and a length up to several tens of micrometers were coated with a layer of ZnS shell by the reaction of zinc acetate and thiourea at 180 °C for 10 h. It was found that uniform ZnS shell was composed of ZnS nanoparticles with a diameter of ca. 4 nm, which anchored on the nanowires without any surface pretreatment. The 1D CdS@ZnS core-shell nanocomposites were confirmed by XRD, SEM, TEM, HR-TEM, ED, and EDS techniques. The optical properties and photocatalytic activities of the 1D CdS@ZnS core-shell nanocomposites towards methylene blue (MB) and 4-chlorophenol (4CP) under visible light (λ > 420 nm) were separately investigated. The results show that the ZnS shell can effectively passivate the surface electronic states of the CdS cores, which accounts for the enhanced photocatalytic activities of the 1D CdS@ZnS core-shell nanocomposites compared to that of the uncoated CdS nanowires

Benefit Assessment of the Integrated Demand Management Concept for Multiple New York Metroplex Airports

Benefits of the Integrated Demand Management (IDM) concept were assessed utilizing a newly developed automated simulation capability called Traffic Management Initiative Automated Simulation (TMIAutoSim). The IDM concept focuses on improving traffic flow management (TFM) by coordinating the FAAs strategic Traffic Flow Management System (TFMS) with its more tactical Time-Based Flow Management (TBFM) system. The IDM concept leverages a new TFMS capability called Collaborative Trajectory Options Program (CTOP) to strategically pre-condition traffic demand flowing into a TBFM-managed arrival environment, where TBFM is responsible for tactically managing traffic by generating precise arrival schedules. The IDM concept was developed over a multi-year effort, focusing on solving New York metroplex airport arrival problems. TMIAutoSim closely mimics NASAs high-fidelity simulation capabilities while enabling more data to be collected at higher speed. Using this new capability, the IDM concept was evaluated using realistic traffic across various weather scenarios. Six representative weather days were selected after clustering three months of historical data. For those selected six days, Newark Liberty International Airport (EWR) and LaGuardia Airport (LGA) arrival traffic scenarios were developed. For each selected day, the historical data were analyzed to accurately simulate actual operations and the weather impact of the day. The current day operations and the IDM concept operations were simulated for the same weather scenarios and the results were compared. The selected six days were categorized into two groups: clear weather for days without Ground Delay Programs (GDP) and convective weather for days with GDP and significant weather around New York metroplex airports. For the clear weather scenarios, IDM operations reduced last minute, unanticipated departure delays for short-haul flights within TBFM control boundaries with minimal to no impact on throughput and total delay. For the convective weather scenarios, IDM significantly reduced delays and increased throughput to the destination airports