The Impact of Infostation Density on Vehicular Data Dissemination

Vehicle-to-Vehicle and Vehicle-to-Roadside communications are going to become an indispensable part of the modern day automotive experience. For people on the move, vehicular networks can provide critical network connectivity and access to real-time information. Infostations play a vital role in these networks by acting as gateways to the Internet and by extending network connectivity. In this context, an important question is “What is the minimum number of infostations that need to be deployed in an area in order to support vehicular applications?” Optimizing infostation density is vital to understanding and reducing the cost of deployment and management. In this paper, we examine the required infostation density in a highway scenario using different data dissemination models. We start from a simple analysis that captures the required density under idealized assumptions. These models are validated by an event-driven simulator. We then run detailed QualNet simulations on both controlled and realistic vehicular traces to observe the information density trends in practical environments, and consequently propose techniques to improve dissemination performance and reduce the required infostation density.     

Investigations on mode-division multiplexed free-space optical transmission for inter-satellite communication link

Wireless Networks - Inter-satellite data transmission links are very crucial for providing global inter-connectivity. We report designing and investigations on high date rate inter-satellite...     

构建一种新型综合性课程的探索

本文针对现有课程设置过程中,课时和知识内容之间的矛盾,借鉴现有综合课程设计的研究成果,提出以实践内容为主体构建综合性课程的方式解决课时安排的矛盾.具体构建方式是以实践类综合设计为平台,在课程中加入新的理论知识,即要求学生在实践中自学理论知识.本文提出的构建方式具有很强的实用性,对于现有教学中存在的一些问题具有很好的指导...     

InP衬底上InAlAs异变缓冲层和高铟组分InGaAs的生长温度优化

利用气态源分子束外延技术在InP衬底上生长了包含InAlAs异变缓冲层的In0.83Ga0.17As外延层.使用不同生长温度方案生长的高铟InGaAs和InAlAs异变缓冲层的特性分别通过高分辨X射线衍射倒易空间图、原子力显微镜、光致发光和霍尔等测量手段进行了表征.结果表明, InAlAs异变缓冲层的生长温度越低, X射线衍射倒易空间图 (004) 反射面沿Qx方向的衍射峰半峰宽就越宽, 外延层和衬底之间的倾角就越大, 同时样品表面粗糙度越高.这意味着材料的缺陷增加, 弛豫不充分.对于生长在具有相同生长温度的InAlAs异变缓冲层上的In0.83Ga0.17As外延层, 采用较高的生长温度时, X射线衍射倒易空间图 (004) 反射面沿Qx方向的衍射峰半峰宽较小, 77K下有更强的光致发光, 但是表面粗糙度会有所增加.这说明生长温度提高后, 材料中的缺陷得到抑制.     

Node cooperation in hybrid ad hoc networks

A hybrid ad hoc network is a structure-based network that is extended using multihop communications. Indeed, in this kind of network, the existence of a communication link between the mobile station and the base station is not required: A mobile station that has no direct connection with a base station can use other mobile stations as relays. Compared with conventional (single-hop) structure-based networks, this new generation can lead to a better use of the available spectrum and to a reduction of infrastructure costs. However, these benefits would vanish if the mobile nodes did not properly cooperate and forward packets for other nodes. In this paper, we propose a charging and rewarding scheme to encourage the most fundamental operation, namely packet forwarding. We use "MAC layering" to reduce the space overhead in the packets and a stream cipher encryption mechanism to provide "implicit. authentication" of the nodes involved in the communication. We analyze the robustness of our protocols against rational and malicious attacks. We show that-using our solution-collaboration is rational for selfish nodes. We also show that our protocols thwart rational attacks and detect malicious attacks.     

Large‐Scale Growth of Two‐Dimensional SnS2 Crystals Driven by Screw Dislocations and Application to Photodetectors

2D SnS₂ crystals are attracting increasing attention owning to the huge potential for electronic and optoelectronic applications. However, batch production of 2D SnS₂ crystals via a simple vapor process remains challenging by far. Moreover, the growth mechanism for vapor growth of 2D SnS₂ is not well documented as well. Herein, a simple approach is presented for preparation of large‐scale 2D SnS₂ crystals on mica sheets and it is demonstrated that these 2D crystals follow a screw‐dislocation‐driven (SDD) spiral growth process. The synthesized 2D crystals show hexagonal and truncated triangular shapes with the lateral size ranging from a few micrometers to dozens of micrometers. Observations of key features for screw dislocations, such as helical fringes, dislocation hillocks, and herringbone contours, solidly confirm the SDD spiral growth behavior of the SnS₂. Possible mechanism is proposed in this work to show the generation and propagation of screw dislocations. Furthermore, in order to explore the optoelectronic property of the SnS₂, photodetectors based on 2D SnS₂ crystals are fabricated. The resulting device shows excellent operating characteristics, including good photo‐stability and reproducibility as well as a fast photoresponse time (≈42 ms), which enable the SnS₂ a promising candidate for photodetectors.     

Ångstrom‐Scale Silver Particles as a Promising Agent for Low‐Toxicity Broad‐Spectrum Potent Anticancer Therapy

Cancer incidence is rising, and the efficacy of current available anticancer agents is limited by severe dose‐limiting toxicities and drug resistance problems. Nanoparticles are heralded as the next frontier in cancer treatment. Here, a pure physical method is used to efficiently fabricate very small silver particles even approaching the Ångstrom (Ång) dimension. Fructose is used as a dispersant and stabilizer to coat the Ång‐scale silver particles (AgÅPs). Functional and mechanistic studies demonstrate that fructose‐coated AgÅPs (F‐AgÅPs) can enter and accumulate in multiple cultured cancer cell lines to induce apoptotic death, whereas most normal cells are resistant to the efficacious dose of F‐AgÅPs; in vivo, intravenous administration of F‐AgÅPs potently inhibits the growth of pancreatic and lung cancer xenografts in nude mice, without inducing notable toxic effects on the healthy tissues. The results suggest the promising potential of F‐AgÅPs as a potent, safe, and broad‐spectrum agent for the cancer treatment.     

Tailoring the Molecular Properties with Isomerism Effect of AIEgens

It is challenging to achieve precise control on the properties of organic π‐functional materials to widen their practical applications. On the other hand, the study of aggregation‐induced emission luminogens (AIEgens) helps achieve such goals because of inherent relationships between their luminescence behaviors and conformational variations that allow for the visual monitoring of the changes in the material properties. Inspired by this, in this work, three AIE isomers are fabricated in structures consisting of tetraphenylpyrazine and triphenylethene units with para‐, meta‐, and ortho‐position linkages, respectively. The isomerism effect brings about significantly decreased luminescence efficiency, subtly blueshifted emission, basically reduced AIE effect but boosted porosity in the aggregate state as the conformation of AIEgens evolves from an extended to a folded one. Based on the distinct properties, their respective use in blue organic light‐emitting diodes, nanofluorescent probes, and molecule‐capturing porous crystals are investigated. This work not only achieves precise property control by using the isomerism effect of AIEgens but also provides useful information on the future design of π‐conjugated materials with advanced functionalities.     

A Deep Learning Spatiotemporal Prediction Framework for Mobile Crowdsourced Services

Mobile Networks and Applications - This papers presents a deep learning-based framework to predict crowdsourced service availability spatially and temporally. A novel two-stage prediction model is...