Waveguide-based near-eye display with dual-channel exit pupil expander

We propose a waveguide-based near-eye display featuring a dual-channel exit pupil expander, which is composed of an in-coupler, relay gratings, and an out-coupler. Unlike the conventional waveguide-based near-eye displays, whose field of views are usually non-split or partially split, our dual-channel exit pupil expander is able to evenly split the field of view into two halves. The greatest benefit of doing so is that the upper limit of field of view could be significantly increased. The design rules for all components, including the microdisplay, collimating lens, waveguide and gratings, have been studied. The refractive index and dimension of waveguide are identified as two factors that limit the field of view. In what follows, its key specifications are recapitulated. Field of view is 70° (diagonal), eye relief is 15 mm, exit pupil is 20 × 9 mm², modulation transfer function is above 0.591 at 30 cycle/degree, contrast ratio is 13, and distortion is 1.38%.     

An array waveguide probe for detection,location and sizing of surface cracks in metals

The paper describes the development of a novel microwave probe for detection, location and sizing of surface cracks in metals. The probe utilizes the inherent mutual coupling in an array structure to determine crack alignment, placement and dimensions. The main feature of the probe is its ability to electronically scan the region of concern, thus avoiding the large inspection time and unwanted noise experienced in the conventional mechanical scanning. Theoretical and experimental results are presented for a prototype two-cell array probe when scanning a metallic specimen containing a long surface crack. It is shown that the probe is capable of determining the orientation, location and dimensions of surface cracks of a few millimeters depth.     

Entropic Contributions to Protein Stability

Thermodynamic stability is an important property of proteins that is linked to many of the trade-offs that characterize a protein molecule and therefore its function. Designing a protein with a desired stability is a complicated task given the intrinsic trade-off between enthalpy and entropy which applies for both the folded and unfolded states. Traditionally, protein stability is manipulated by point mutations which regulate the folded state enthalpy. In some cases, the entropy of the unfolded state has also been manipulated by means that drastically restrict its conformational dynamics such as engineering disulfide bonds. In this mini-review, we survey various approaches to modify protein stability by manipulating the entropy of either the unfolded or the folded states. We show that point mutations that involve elimination of long-range contacts may have a greater destabilization effect than mutations that eliminate shorter-range contacts. Protein conjugation can also affect the entropy of the unfolded state and thus the overall stability. In addition, we show that entropy can contribute to shape the folded state and yield greater protein stabilization. Hence, we argue that the entropy component can be practically manipulated both in the folded and unfolded state to modify protein stability.     

Fabrication and characterization of large-core Yb/Al-codoped fused silica waveguides using dry etching

A deep inductively coupled plasma etching process was developed as a part of a continuous effort to develop an all-silica on-chip platform for high-power optical devices. Combined F and Cl based etching chemistry was found most suitable since silica matrix and Al doping are generally etched using different chemistries. First large-core (∼20 × 20 μm) Yb/Al-codoped fused silica waveguides on pure silica substrate were successfully fabricated, featuring ∼1 dB/cm optical propagation loss.     

Use of electromagnetic two-layer wave-guided propagation in the GPR frequency range to characterize water transfer in concrete

The objective of this paper is to adapt a recent innovative technique for extracting and exploiting the Electromagnetic (EM) waveguide dispersion of civil engineering materials by means of GPR, and allowing to monitor the water ingress front during the absorption process for various concrete mixes. This technique is based on an inversion procedure that applies the Electromagnetic Waveguide Model (WGM) to invert phase velocity dispersion curves in their modal form. A Parallel homogenization model, derived from the Lichtenecker-Rother equation, has been employed to extend the waveguide model from a one-layer to a two-layer medium. The WGM outputs are then used to estimate the geometric parameters of the propagation medium and offer a primary application to water transfer monitoring in concrete through capillarity effects. The initial WGM validation is carried out on FDTD-simulated propagation signals, while the second validation relies on GPR data acquired from homogeneous materials. Then, a broad-based experimental study is conducted for the purpose of correlating electromagnetic waveguide dispersion parameters with both the geometric and hydric characteristics of various concrete mixes. Results obtained using the two-layer WGM serve to monitor the water ingress front during an absorption process. These results are then compared to the moisture gradients generated on cores using gammadensimetry, which is set as the reference. This procedure yields a number of trends, which in turn provide key information on the conditioning state of the studied concretes.     

双脊型波导窗在宽带大功率行波管中的应用

本文简要分析了脊形波导窗的结构,介绍了WRD650双脊波导窗在实际制管中的应用,测试结果表明脊形波导窗应用于宽带大功率行波管是可行的.     

薄壁钢结构的材料和几何非线性等参样条有限条法的研究进展

给出了等参样条有限条法(ISFSM)用于分析开孔薄壁钢结构的材料非弹性和几何非线性的研究进展。简要介绍了ISFSM理论。提出了运动学方程、应力-位移关系和假定的本构关系。通过增量平衡条件,推导出正切刚度矩阵。讨论了板带连续和边界条件的要求。特别强调了塑性理论和求解速率方程的方法,以及相关的欧拉后退法和材料模量一致的假定。开孔薄壁钢结构的非弹性后屈曲性能分析的准确性和有效性,证实了目前的等参样条有限条法的有效性。     

0.22THz折叠波导行波管放大器理论分析与数值模拟

为了解折叠波导行波管放大器的性能影响因素,在理论分析的基础上,对0.22 THz折叠波导行波管放大器进行系统的数值模拟与分析,重点讨论电子束压、束流、输入信号功率、结构周期数、材料电导率、引导磁场大小、电子能散度以及发射度对器件输出功率水平的影响.发现束压存在最佳工作范围,增加束流可以有效提高器件增益;输入信号不宜过强...     

Alkaline aluminum phosphate glasses for thermal ion-exchanged optical waveguide

Alkaline aluminum phosphate glasses (NMAP) with excellent chemical durability for thermal ion-exchanged optical waveguide have been designed and investigated. The transition temperature Tg (470 °C) is higher than the ion-exchange temperature (390 °C), which is favorable to sustain the stability of the glass structure for planar waveguide fabrication. The effective diffusion coefficient D_e of K⁺–Na⁺ ion exchange in NMAP glasses is 0.110 μm²/min, indicating that ion exchange can be achieved efficiently in the optical glasses. Single-mode channel waveguide has been fabricated on Er³⁺/Yb³⁺ doped NMAP glass substrate by standard micro-fabrication and K⁺–Na⁺ ion exchange. The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber. Judd–Ofelt intensity parameter Ω₂ is 5.47 × 10⁻²⁰ cm², implying a strong asymmetrical and covalent environment around Er³⁺ in the optical glasses. The full width at half maximum and maximum stimulated emission cross section of the ⁴I_13/2 → ⁴I_15/2 are 30 nm and 6.80 × 10⁻²¹ cm², respectively, demonstrating that the phosphate glasses are potential glass candidates in developing compact optoelectronic devices. Pr³⁺, Tm³⁺ and Ho³⁺ doped NMAP glasses are promising candidates to fabricate waveguide amplifiers and lasers operating at special telecommunication windows.     

自主水下航行器折叠天线设计

通过对水下机器人的主体外形以及传统水下机器人的外附体进行建模,运用CFD流体软件对其进行仿真分析,发现自主水下航行器外附体中,天线产生阻力最大。天线是自主水下航行器必不可少的通信模块。针对天线带来的大阻力问题,设计出两种折叠天线机构。运用ADAMS软件对比了两种折叠天线机构运动性能参数;运用SolidWorks的应力仿真模块分析了折叠天线各个部分的耐压强度。结果表明折叠天线的应用能为自主水下航行器性能产生积极影响,为自主水下航行器的设计提供参考。