Investigation of non-line-of-sight underwater optical wireless communications with wavy surface.

Underwater optical wireless communication (UOWC) systems have been widely researched to achieve high-speed and secure wireless communications. The non-line-of-sight (NLOS) UOWC system that uses the water surface to reflect signal light is widely studied to overcome the line-of-sight (LOS) channel limitation, particularly the channel blockage issue by marine biology or complex underwater topography. However, most previous NLOS UOWC studies have assumed a flat water surface or a general sine or cosine surface wave model for simplicity, leading to inaccurate performance estimations. In this paper, we build a theoretical NLOS UOWC framework with the Pierson wave model which considers both spatial correlation and time relativity information of wave incorporating wind speed, and investigate the signal-noise-ratio (SNR) and bit-error-rate (BER) performance. Results show that compared with the previous flat surface, the wavy surface can reduce the probability of achieving a satisfying signal level by up to 70%, affecting the performance of NLOS UOWC systems. Furthermore, we investigate the multiple-input-multiple-output (MIMO)-based NLOS UOWC under wavy surfaces. Results show that the MIMO principle can reduce the impact of the wavy surface, where the probability of achieving a satisfying signal level can be increased by up to 50% using the 2 × 4 MIMO configuration. However, results also show that further increasing the number of receivers may not further improve the system performance. The proposed model enables more accurate design and analysis of NLOS UOWC systems by accounting for the overlooked impact of wavy surfaces.

In situ characterization of thermal cleaned surface for preparing superior transmission-mode GaAs photocathodes.

Considering that it is impractical to utilize in situ surface diagnostic means to determine the surface cleanliness of transmission-mode GaAs photocathodes in the vacuum device manufacturing process, the thermal desorption technique with the aid of the quadrupole mass spectrometer during the thermal cleaning process is employed to in situ characterize the thermal cleaned surface. The desorption behaviors for various impurity gases during the thermal cleaning process are analyzed. The experimental results show that the amount of desorbed impurity gases varies due to the different heat treatment temperatures. Through the verification of Cs/O activation and quantum efficiency measurement, it is found that the desorption behaviors of the specific impurity gases including AsH3 and As2 are crucial to surface cleanliness of transmission-mode GaAs photocathodes, which relate to the final photoemission capability. This simple and reliable criterion provides an effective way to guide the thermal cleaning process of transmission-mode GaAs photocathodes, and the desorption behaviors assist in in situ evaluation of surface cleanliness.

Derivatization for the simultaneous LC/MS quantification of multiple neurotransmitters in extracellular fluid from rat brain microdialysis.

Quantification of amino acid based neurotransmitters in extracellular fluids, such as those in the neuron synapse, presents a challenge to the analytical chemistry because of the absence of UV- or fluorescence-detectable functional groups and the low sensitivity in mass spectrometric detection. This report describes a novel use of the succinimide reagent, N-α-Boc-l-tryptophan hydroxysuccinimide ester (Boc-TRP), for the pre-column derivatization to simultaneously quantify multiple neurotransmitters in the rat brain microdialysis samples. The Boc-TRP derivatization was rapid and quantitative in phosphate the buffer (pH 7.4) at room temperature. The derivatized neurotransmitters were suitable for rapid LC/MS quantification with less than 3-min chromatographic separation. The Boc-group in the derivatized product generated unique fragmentation patterns in the triple quadrupole mass spectrometric analysis under Multiple Reaction Monitoring mode and significantly increased the specificity and sensitivity. The derivatization and rapid LC/MS quantification method developed in this study showed a linear dynamic range from single digit nM to 1000nM with coefficient greater than 0.990. At the LOQ, the accuracy ranged from 95 to 108% and the precision (CV%) was less than 20%. Since there was no concentration and reconstitution in the sample workup process, this derivatization approach simplified the neurotransmitter quantification of the brain microdialysis samples.

Facile synthesis of azaspirocycles via iron trichloride-promoted cyclization/chlorination of cyclic 8-aryl-5-aza-5-tosyl-2-en-7-yn-1-ols.

A simple and efficient FeCl(3)-promoted cyclization/chlorination of cyclic tosylamine-tethered 8-aryl-2-en-7-yn-1-ols was observed. The reaction proceeded instantaneously at 23 °C in air to afford (Z)-4-(arylchloromethylene)-substituted azaspirocycles in good to excellent yields. This transformation can also be applied to the synthesis of spirocarbocyclic analogues from cyclic 8-aryl-2-en-7-yn-1-ols and FeCl(3).