M-110

Topologically distinct Weyl fermion pairs

A Weyl semimetal has Weyl nodes that always come in pairs with opposite chiralities. Notably, different ways of connection between nodes are possible and would lead to distinct topologies. Here we identify their differences in many respects from two proposed models with different vorticities. One prominent feature is the behaviour of zeroth Landau levels (LLs) under magnetic field. We demonstrate that the magnetic tunneling does not always expel LLs from zero energy because the number of zero-energy modes is protected by the vorticity of the Weyl nodes, instead of the chirality. Other respects in disorder effects for weak (anti-)localization, surface Fermi arcs, and Weyl-node annihilation, are interesting consequences that await more investigation in the future.

Compact MZI modulators on thin film Z-cut lithium niobate

In this paper, we designed, implemented, and characterized compact Mach-Zehnder interferometer-based electro-optic modulators. The modulator utilizes spiral-shaped optical waveguides on Z-cut lithium niobate and the preeminent electro-optic effect which is applied using top and bottom electrodes. Optical waveguides are made of rib etched lithium niobate waveguides with bottom silicon oxide cladding, while SU8 polymer covers the top and sides of the rib waveguides. The proposed implementation resulted in low optical losses < 1.3 dB/cm. Moreover, we achieved compact modulators that fit 0.286 cm and 2 cm long optical waveguides in 110 ?m × 110 ?m and 300 ?m × 300 ?m areas, respectively. For single arm modulation, the modulators achieved a VπL of 7.4 V.cm and 6.4 V.cm and 3-dB bandwidths of 9.3 GHz and 2.05 GHz, respectively. Push-pull modulation is expected to cut these VπL in half. The proposed configuration avoids traveling wave modulation complexities and represents a key development towards miniature and highly integrated photonic circuits.

Near-Infrared-II Semiconducting Polymer Dots for Deep-tissue Fluorescence Imaging

Fluorescence imaging, particularly in the NIR-II region (1000-1700 nm), has become an unprecedented tool for deep-tissue in vivo imaging. Among the fluorescent nanoprobes, semiconducting polymer nanoparticles (Pdots) appear to be a promising agent because of their tunable optical and photophysical properties, ultrahigh brightness, minimal autofluorescence, narrow-size distribution, and low cytotoxicity. This review elucidates the recent advances in Pdots for deep-tissue fluorescence imaging and the facing future translation to clinical use.

Effects of titanium with different micro/nano structures on the ability of osteoblasts to resist oxidative stress

Excessive accumulation of oxidative intermediates in the elderly significantly aggravates bone degradation and hinders the osseointegration of topological titanium (Ti) implants. Thus, it is of great significance to evaluate the antioxidant and osteoinduction capabilities of various nano, micro or micro/nano-composite structures under oxidative stress (OS) microenvironment. In this study, we discovered that 110 nm titania nanotubes (TNTs) enhanced the adsorption of fibronectin (FN) proteins onto smooth and rough titanium surfaces to varying degrees. Compared with Ti and 30 nm TNTs (T₃₀) groups, cells on 110 nm TNTs (T₁₁₀), microstructure/30 nm TNTs (M₃₀) and microstructure/110 nm TNTs (M₁₁₀) had smaller area, lower reactive oxygen species (ROS), and better proliferation/osteogenic differentiation abilities under OS condition, but there was no significant difference among the three groups. In addition, combined with our previous study, we suggested that T₁₁₀, M₃₀ and M₁₁₀ resistance to OS was also strongly associated with the high expression of FN-receptor integrin α5 or β1. All the findings indicated that the micro/nano-composed structures (M₃₀ & M₁₁₀) had similar anti-oxidation and osteogenesis abilities to T₁₁₀, which provided guidance for the application of different titanium implants with different topologies in the elderly.

Spatial variability of outdoor exposure to radiofrequency radiation from mobile phone base stations, in Khartoum, Sudan

The wide-spread exposure to constantly evolving wireless technologies believed to pose a serious health threat. Human beings are persistently exposed to RF radiation from mobile phones and their base stations. The current study aimed at classifying and characterizing the exposure to RF radiation from the mobile phone base stations. Spatial distribution measurements were carried out in Khartoum city during two time periods, first in 2012 (pilot survey) and again during Sept. 2019-Jan. 2020, to cover a total of 282 antennas operating with GSM900, GSM1800, and UMTS2100. The tested antennas belong to three mobile communication companies namely Sudani, Zain, and MTN companies, that randomly coded into company A, company B, and company C for security purposes. Measurements were performed using frequency-selective RF analyzer at fixed distances from the antennas/towers. Data were subjected to advanced repeated measures ANOVA, linear discriminant analysis (LDA), and spatial interpolation with ArcGIS. The averages of GSM900, GSM1800, and UMTS measurements were 0.01933 W/m², 0.0067 W/m², and 0.0046 W/m². The high levels of power densities for each single antenna were recorded at 90 m, 110 m, 130 m, and at 150 m distances, for the majority (70%) of the measured antennas and the peak/highest values reported mainly at 110 m distance. Conversely, the discriminant loadings as part of LDA, suggested that, much of variance among measurements is attributed to measurements at 150 m, 170 m, and 190 m distances, while visual illustration of group centroids implied that, the RF signals of the different companies were measured separately which support accuracy of frequency-selective measurements. The LDA has confirmed the ANOVA results that, the overall difference between the three companies was statistically significant for UMTS, and GSM900 measurements but not significant for GSM1800 measurements. Kriging interpolation using ArcGIS provided a strong evidence of great spatial distribution of exposure across the study area, with market places and typical urban residential quarters showing highest levels of RF. Few extreme values exceeding ICNIRP limits are reported but excluded from the calculations because of an issue of normality of data that is considered a prerequisite for parametric data analysis. Existence of extreme levels of RF indicates a need for further investigation and some antennas of Company B are mounted on towers belongs to Company C, implying multi exposure. Unexpected pattern of RF levels continued to increase up to 190 m distance and possibly beyond 190 m is reported for UMTS measurements of Company C.