Beihang University

About: Beihang University is a education organization based out in Beijing, China. It is known for research contribution in the topics: Computer science & Control theory. The organization has 67002 authors who have published 73507 publications receiving 975691 citations. The organization is also known as: Beijing University of Aeronautics and Astronautics.

Charge and phonon transport in PbTe-based thermoelectric materials

Abstract: PbTe is a typical intermediate-temperature thermoelectric material, which has undergone extensive developments and achieved excellent high thermoelectric performance. In this perspective we summarized several strategies that were successfully applied in PbTe-based thermoelectric materials through manipulating charge and phonon transports, such as optimizing carrier density to tune Fermi level, tailoring band structure to enhance effective mass, and designing all-scale hierarchical architectures to suppress phonon propagation. Meanwhile, due to the different features of conduction and valence bands, we separately introduced the approaches to enhance performance of p-type and n-type PbTe. In p-type PbTe, the strategies of band convergence, band alignment and density of state (DOS) distortion are more effective to achieve high electrical transport properties. By contrast, flattening conduction bands and introducing deep impurity level are more suitable for n-type PbTe. Lastly, several potential strategies were proposed to further improve the thermoelectric performance of PbTe-based materials, which might be extended to other thermoelectric systems.

Global and regional molecular epidemiology of HIV-1, 1990–2015: a systematic review, global survey, and trend analysis

Abstract: Summary Background Global genetic diversity of HIV-1 is a major challenge to the development of HIV vaccines. We aimed to estimate the regional and global distribution of HIV-1 subtypes and recombinants during 1990–2015. Methods We searched PubMed, EMBASE (Ovid), CINAHL (Ebscohost), and Global Health (Ovid) for HIV-1 subtyping studies published between Jan 1, 1990, and Dec 31, 2015. We collected additional unpublished HIV-1 subtyping data through a global survey. We included prevalence studies with HIV-1 subtyping data collected during 1990–2015. We grouped countries into 14 regions and analysed data for four time periods (1990–99, 2000–04, 2005–09, and 2010–15). The distribution of HIV-1 subtypes, circulating recombinant forms (CRFs), and unique recombinant forms (URFs) in individual countries was weighted according to the UNAIDS estimates of the number of people living with HIV (PLHIV) in each country to generate regional and global estimates of HIV-1 diversity in each time period. The primary outcome was the number of samples designated as HIV-1 subtypes A, B, C, D, F, G, H, J, K, CRFs, and URFs. The systematic review is registered with PROSPERO, number CRD42017067164. Findings This systematic review and global survey yielded 2203 datasets with 383 519 samples from 116 countries in 1990–2015. Globally, subtype C accounted for 46·6% (16 280 897/34 921 639 of PLHIV) of all HIV-1 infections in 2010–15. Subtype B was responsible for 12·1% (4 235 299/34 921 639) of infections, followed by subtype A (10·3%; 3 587 003/34 921 639), CRF02_AG (7·7%; 2 705 110/34 921 639), CRF01_AE (5·3%; 1 840 982/34 921 639), subtype G (4·6%; 1 591 276/34 921 639), and subtype D (2·7%; 926 255/34 921 639). Subtypes F, H, J, and K combined accounted for 0·9% (311 332/34 921 639) of infections. Other CRFs accounted for 3·7% (1 309 082/34 921 639), bringing the proportion of all CRFs to 16·7% (5 844 113/34 921 639). URFs constituted 6·1% (2 134 405/34 921 639), resulting in recombinants accounting for 22·8% (7 978 517/34 921 639) of all global HIV-1 infections. The distribution of HIV-1 subtypes and recombinants changed over time in countries, regions, and globally. At a global level during 2005–15, subtype B increased, subtypes A and D were stable, and subtypes C and G and CRF02_AG decreased. CRF01_AE, other CRFs, and URFs increased, leading to a consistent increase in the global proportion of recombinants over time. Interpretation Global and regional HIV diversity is complex and evolving, and is a major challenge to HIV vaccine development. Surveillance of the global molecular epidemiology of HIV-1 remains crucial for the design, testing, and implementation of HIV vaccines. Funding None.

Electrospun FeS2@Carbon Fiber Electrode as a High Energy Density Cathode for Rechargeable Lithium Batteries

Abstract: In this study, an FeS2@carbon fiber electrode is developed with FeS2 nanoparticles either embedded in or attached to carbon fibers by using an electrospinning method. By applying this binder-free, metal-current-collector-free FeS2@carbon fiber electrode, both the redox reaction and capacity decay mechanisms for the Li–FeS2 system are revealed by changing the electrolyte (conventional carbonate electrolyte and a “solvent-in-salt”-type Li–S battery electrolyte) and working voltage ranges (1.0–3.0 V and 1.5–3.0 V vs Li/Li+). The FeS2@carbon fiber electrode shows stable cycling performance in both the conventional carbonate electrolyte and the solvent-in-salt-type Li–S battery electrolyte in the voltage range of 1.5–3.0 V. Electrochemical tests in the solvent-in-salt-type Li–S battery electrolyte indicate that the Li–FeS2 system becomes a hybrid of the Li–S cell and Li–iron sulfide cell after the initial cycle. Based on the understanding on the capacity decay mechanisms, the cycling stability of the Li–FeS2 s...

Adaptive optoelectronic camouflage systems with designs inspired by cephalopod skins

Abstract: Octopus, squid, cuttlefish, and other cephalopods exhibit exceptional capabilities for visually adapting to or differentiating from the coloration and texture of their surroundings, for the purpose of concealment, communication, predation, and reproduction. Long-standing interest in and emerging understanding of the underlying ultrastructure, physiological control, and photonic interactions has recently led to efforts in the construction of artificial systems that have key attributes found in the skins of these organisms. Despite several promising options in active materials for mimicking biological color tuning, existing routes to integrated systems do not include critical capabilities in distributed sensing and actuation. Research described here represents progress in this direction, demonstrated through the construction, experimental study, and computational modeling of materials, device elements, and integration schemes for cephalopod-inspired flexible sheets that can autonomously sense and adapt to the coloration of their surroundings. These systems combine high-performance, multiplexed arrays of actuators and photodetectors in laminated, multilayer configurations on flexible substrates, with overlaid arrangements of pixelated, color-changing elements. The concepts provide realistic routes to thin sheets that can be conformally wrapped onto solid objects to modulate their visual appearance, with potential relevance to consumer, industrial, and military applications.