High-efficiency ultrathin metasurfaces with simultaneous control of complete phase, amplitude, and polarization.

Metasurfaces that can simultaneously manipulate both amplitude and phase have garnered interest and have promising applications owing to their strong beam-steering ability; however, achieving a high maximum transmission while covering the full phase shift remains challenging. This paper proposes a chiral-structured meta-atom composed of two external cross-polarized patches and an internal coupling structure. It enables the independent modulation of the phase, amplitude, and polarization at large incidence angles and ensures a high maximum transmission with a complete phase shift enabled by the two internal rotation structures. The transmission phase and amplitude can be independently controlled by adjusting the geometry and rotation angle of the meta-atoms. The performance and feasibility of the method were verified using an ultra-thin high-order Bessel beam generator sample with a thickness of 2 mm (about λ0/11 at 14 GHz). This design can meet arbitrary requirements for extreme beam steering and has broad application prospects in the fields of electromagnetism and photonics.

Vortex-electromagnetic-wave-based ISAR imaging for high-speed maneuvering targets.

Vortex electromagnetic wave (VEMW) carrying orbital angular momentum (OAM), which is expected to introduce additional degrees of freedom in inverse synthetic aperture radar(ISAR) imaging. However, the current research about maneuvering targets is based on the "stop go" hypothesis, which does not apply to high-speed motion scenarios due to the intrapulse movement of the target. To improve the imaging quality, this letter proposes a VEMW-based high-speed maneuvering targets imaging method. Firstly, the ISAR imaging scenario of high-speed target is established. According to the spatial geometric relationship between radar and maneuvering target, the vortex echo is deduced and its characteristics are analyzed. Subsequently, a frequency modulation rate estimation method considering both calculation efficiency and high precision is proposed to realize the accurate estimation of target speed. Then, an adaptive azimuth image compensation method based on minimum entropy is proposed. Through the setting of threshold, the number of component signals in linear frequency modulation (LFM) signal is determined and compensated successively. Finally, the range profile and azimuth profile are combined to reconstruct the three-dimensional information. The simulation results demonstrate that this work can effectively eliminate the influence of high-speed motion on range and azimuth profile, also benefit the development of ISAR imaging technique of high-speed maneuvering targets.

Generation of plane spiral orbital angular momentum using circular double-slot Vivaldi antenna array.

A novel and feasible solution to generate plane spiral orbital angular momentum (PSOAM) vortex beam is proposed in this paper. The general principle of generating PSOAM in circular antenna array (CAA) is deduced, and verified by the simulation of the dipole CAA. Four double-slot Vivaldi antenna elements connect sequentially and are inserted into a CAA, which makes the proposed antenna easily fabricated and fully miniaturized. Both simulated and measured results show that it can generate PSOAM with l = 3 (l is the mode number of vortex wave) at 5 GHz. The vortex phase of l = 3 is observed, the measured peak gain is 5.7 dB. The VSWR remains below 2 from 4 to 6 GHz, which shows the impedance bandwidth of S11 < -10 dB is more than 40%.

Delays and Pathways to Final Tuberculosis Diagnosis in Patients from a Referral Hospital in Urban China.

AbstractChina is among the countries with the largest epidemic of drug susceptible and resistant tuberculosis globally. We investigated the locations tuberculosis patients visited before being diagnosed, total diagnostic delay, and risk factors associated with total delay from a large tuberculosis referral hospital in Nanjing, China. We conducted a retrospective cohort study among tuberculosis patients who initiated anti-tuberculosis treatment within 3 months prior to the study date. Patient information regarding time and locations visited while seeking care for tuberculosis-related symptoms was collected through face-to-face interviews. Crude and adjusted Cox proportional hazard ratios of factors associated with time to diagnosis were calculated. Of 179 bacteriologically confirmed patients, 37% were women and median age was 41 (interquartile range [IQR], 26-62). Public hospitals were the most commonly visited health-care institution and repeated visits to them were common. The mean days to tuberculosis diagnosis were 50.3. Female patients (hazard ratio [HR], 1.29; 95% confidence interval [CI], 1.04-1.48) or patients who contacted a health-care provider 2 weeks after becoming symptomatic (HR, 1.59; 95% CI, 1.43-1.70) were significantly less likely to have a timely diagnosis. In a referral hospital in urban China, we found that female tuberculosis patients took significantly more time to reach diagnosis than males and patients often cycled in public hospitals for multiple visits before reaching final diagnosis. Health professionals at public hospitals in Nanjing should be encouraged to refer potential tuberculosis patients as soon as possible to avoid nosocomial transmission.

Al-free Zr-zeolite beta as a regioselective catalyst in the Meerwein-Ponndorf-Verley reaction.

Al-free Zr-zeolite beta catalyzes the transfer reduction of ketones to the corresponding alcohols in high yield and with exceptional stereocontrol. Notably, the catalyst is very robust and gives good results even with 10% water content in the reaction mixture.

Coordination modulation induced synthesis of nanoscale Eu(1-x)Tb(x)-metal-organic frameworks for luminescent thin films.

Strategies for synthesizing of nanoscale single or bimetallic lanthanide metal-organic framework (MOF) materials and their transformation into Eu(1-x)Tb(x)-MOF thin films are reported. The thin films prepared via spin coating deposition method are smooth, dense and mechanically stable. They also exhibit marked luminescent properties and efficient Tb(3+)-to-Eu(3+) energy transferability.

Dynamic kinetic resolution of secondary alcohols combining enzyme-catalyzed transesterification and zeolite-catalyzed racemization.

Hydrophobic zeolite beta containing low concentrations of Zr or Al was found to be a good catalyst for the racemization of 1-phenylethanol. The formation of styrene as a side product could be minimized by reducing the metal concentration in the zeolite beta. Combined with an immobilized lipase from Candida antarctica, the dynamic kinetic resolution of 1-phenylethanol to the (R)-phenylethylester can be achieved with high yield and selectivity. The reaction was best conducted in toluene as solvent at 60 degrees C, with higher temperatures leading to a loss in the enantioselectivity of the formed ester. By using high-molecular-weight acyl-transfer reagents, such as vinyl butyrate or vinyl octanoate, a high enantiomeric excess of the product esters of 92 and 98 %, respectively, could be achieved. This is attributed to a steric effect: the bulky ester is less able to enter the pore space of the zeolite catalyst where the active sites for racemization are localized. Close to 100 % conversion of the alcohol was achieved within 2 h. If the more common acyl donor, isopropenyl acetate, was used, the enantiomeric excess (ee) of the formed ester was only 67 %, and the reaction was considerably slower.