Optical spectroscopy study on single crystalline LaFeAsO

Millimeter-sized single crystals of LaFeAsO were grown from NaAs flux and the in-plane optical properties were studied over a wide frequency range. A sizable electronic correlation effect was indicated from the analysis of the free-carrier spectral weight. With decreasing temperature from 300 K, we observed a continuous suppression of the spectral weight near 0.6 eV. But a spin-density-wave gap formation at lower energy scale was seen only in the broken-symmetry state. We elaborate that both the itinerancy and local spin interactions of Fe\emph{3d} electrons are present for the FeAs-based systems; however, the establishment of the long-range magnetic order at low temperature has a dominantly itinerant origin.Comment: 4 figures, 5 page

Measuring topic network centrality for identifying technology and technological development in online communities

Online communities are a rapidly growing knowledge repository that provides scholarly research, technical discussion, and social interactivity. This abundance of online information increases the difficulty of keeping up with new developments difficult for researchers and practitioners. Thus, we introduced a novel method that analyses both knowledge and social sentiment within the online community to discover the topical coverage of emerging technology and trace technological trends. The method utilizes the Weibull distribution and Shannon entropy to measure and link social sentiment with technological topics. Based on question-and-answer and social sentiment data from Zhihu, which is an online question and answer (Q&A) community with high-profile entrepreneurs and public intellectuals, we built an undirected weighting network and measured the centrality of nodes for technology identification. An empirical study on artificial intelligence technology trends supported by expert knowledge-based evaluation and cognition provides sufficient evidence of the method's ability to identify technology. We found that the social sentiment of hot technological topics presents a long-tailed distribution statistical pattern. High similarity between the topic popularity and emerging technology development trends appears in the online community. Finally, we discuss the findings in various professional fields that are widely applied to discover and track hot technological topics

Avoiding the Detector Blinding Attack on Quantum Cryptography

We show the detector blinding attack by Lydersen et al [1] will be ineffective on most single photon avalanche photodiodes (APDs) and certainly ineffective on any detectors that are operated correctly. The attack is only successful if a redundant resistor is included in series with the APD, or if the detector discrimination levels are set inappropriately