Wright-Patterson Air Force Base

About: Wright-Patterson Air Force Base is a other organization based out in Wright-Patterson AFB, Ohio, United States. It is known for research contribution in the topics: Laser & Mach number. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

A novel approach for embedding communication symbols into physical radar waveforms

Abstract: Due to constantly increasing demand from commercial communications, defense applications are losing spectrum while still striving to maintain legacy capabilities, not to mention the need for enhanced performance. Consequently, ongoing research is focused on developing multi-function methods to share spectrum between radar and military communication. One approach is to incorporate information-bearing communication symbols into the emitted radar waveforms. However, varying the radar waveform during a coherent processing interval (CPI) causes range sidelobe modulation (RSM) that results in increased residual clutter in the range-Doppler response, thus leading to reduced target visibility. Here a novel approach is proposed to embed information into radar emissions while preserving constant envelope waveforms with good spectral containment. Information sequences are implemented using continuous phase modulation (CPM) and phase-attached to a polyphase-coded frequency-modulated (PCFM) radar waveform, the implementation of which is also derived from CPM. The resulting communication-embedded radar waveforms therefore maintain high power and spectral efficiency. More importantly, the adjustable parameterization of the proposed approach enables direct control of the degree of RSM by trading off bit error rate (BER) and/or data throughput.

Light-induced liquid crystallinity

Abstract: A new class of liquid crystals is reported that undergoes light-induced ordering and order-increasing phase transitions; possible applications include ophthalmic devices, such as variable transmission sunglasses. As a rule, photoresponsive liquid crystals such as azobenzenes become structurally disordered on exposure to light. In a few instances, however, the reverse has been reported, so that in certain conditions the crystals can become more ordered. Here, Kosa et al. demonstrate a new class of naphthopyran-based liquid crystals that takes the latter behaviour much further, displaying a variety of ordering transitions: from isotropic to nematic, from isotropic to cholesteric and from nematic to smectic. With appropriate functionalization of the naphthopyran dyes, their isotropic-to-nematic transition results in a clear to strongly absorbing dichroic state. These properties could be useful in a variety of applications, not least in ophthalmic devices such as polarized variable-transmission sunglasses. Liquid crystals are traditionally classified as thermotropic, lyotropic or polymeric, based on the stimulus that governs the organization and order of the molecular system1. The most widely known and applied class of liquid crystals are a subset of thermotropic liquid crystals known as calamitic, in which adding heat can result in phase transitions from or into the nematic, cholesteric and smectic mesophases. Photoresponsive liquid-crystal materials and mixtures can undergo isothermal phase transitions if light affects the order parameter of the system within a mesophase sufficiently. In nearly all previous examinations, light exposure of photoresponsive liquid-crystal materials and mixtures resulted in order-decreasing photo-induced isothermal phase transitions2. Under specialized conditions, an increase in order with light exposure has been reported, despite the tendency of the photoresponsive liquid-crystal system to reduce order in the exposed state3,4,5,6,7. A direct, photo-induced transition from the isotropic to the nematic phase has been observed in a mixture of spiropyran molecules and a nematic liquid crystal8. Here we report a class of naphthopyran-based materials that exhibit photo-induced conformational changes in molecular structure capable of yielding order-increasing phase transitions. Appropriate functionalization of the naphthopyran molecules leads to an exceedingly large order parameter in the open form, which results in a clear to strongly absorbing dichroic state. The increase in order with light exposure has profound implications in optics, photonics, lasing and displays and will merit further consideration for applications in solar energy harvesting. The large, photo-induced dichroism exhibited by the material system has been long sought in ophthalmic applications such as photochromic and polarized variable transmission sunglasses.

High-Temperature and High-Energy-Density Dipolar Glass Polymers Based on Sulfonylated Poly(2,6-dimethyl-1,4-phenylene oxide).

Abstract: A new class of high-temperature dipolar polymers based on sulfonylated poly(2,6-dimethyl-1,4-phenylene oxide) (SO2 -PPO) was synthesized by post-polymer functionalization. Owing to the efficient rotation of highly polar methylsulfonyl side groups below the glass transition temperature (Tg ≈220 °C), the dipolar polarization of these SO2 -PPOs was enhanced, and thus the dielectric constant was high. Consequently, the discharge energy density reached up to 22 J cm-3 . Owing to its high Tg , the SO2 -PPO25 sample also exhibited a low dielectric loss. For example, the dissipation factor (tan δ) was 0.003, and the discharge efficiency at 800 MV m-1 was 92 %. Therefore, these dipolar glass polymers are promising for high-temperature, high-energy-density, and low-loss electrical energy storage applications.