Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors

We address the design of opportunistic spectrum access (OSA) strategies that allow secondary users to independently search for and exploit instantaneous spectrum availability. Integrated in the joint design are three basic components: a spectrum sensor that identifies spectrum opportunities, a sensing strategy that determines which channels in the spectrum to sense, and an access strategy that decides whether to access based on imperfect sensing outcomes. We formulate the joint PHY-MAC design of OSA as a constrained partially observable Markov decision process (POMDP). Constrained POMDPs generally require randomized policies to achieve optimality, which are often intractable. By exploiting the rich structure of the underlying problem, we establish a separation principle for the joint design of OSA. This separation principle reveals the optimality of myopic policies for the design of the spectrum sensor and the access strategy, leading to closed-form optimal solutions. Furthermore, decoupling the design of the sensing strategy from that of the spectrum sensor and the access strategy, the separation principle reduces the constrained POMDP to an unconstrained one, which admits deterministic optimal policies. Numerical examples are provided to study the design tradeoffs, the interaction between the spectrum sensor and the sensing and access strategies, and the robustness of the ensuing design to model mismatch.Comment: 43 pages, 10 figures, submitted to IEEE Transactions on Information Theory in Feb. 200

A cross-cultural analysis of English and Chinese business faxes: a genre perspective

This paper develops a theoretical framework based on genre analysis and crosscultural persuasion for comparing English and Chinese business faxes. Although extensive research has been done in genre analysis and second language writing, scarce literature can be found in cross-cultural genre study of business faxes. Specifically this paper compares faxes used in New Zealand and China. It has been found that English faxes and Chinese faxes are used differently in a number of areas, especially in persuasive orientations. Chinese faxes have a much stronger emphasis on affective aspect useful for building business relationships. This difference is also found in rhetorical structure and linguistic strategies. For example, logos has been identified as a major persuasive orientation in English faxes while both qing or pathos and li or logos were seen as important for Chinese faxes

Reflection on College Education and Teaching Management under New Media

Under the background of current social development, the role of media in the process of information dissemination is becoming more and more enlarged, the speed of information dissemination is greatly accelerated based on the platform built by the media. In the process of information dissemination, the related concepts of new media are derived based on the media platform. This is also the result of the continuous integration of information technology and network technology. Compared with the traditional media, the advantages of new media technology itself are more obvious both the source of information, but also the reporter and audience, so in the context of the development of new media art, the spread of various social hot issues is very fast, and the coverage is also wider. Under the background of the development of new media, colleges and universities themselves are greatly impacted by the information of new media, because people have higher acceptance of new media, so they receive all kinds of information from the outside world through mobile phones and computers, which leads to the challenge of education and teaching management in colleges and universities at present

Far-Field Optical Microscopy Based on Stimulated Emission Depletion

Conventional lens-based (far-field) fluorescence microscopy is a widely used imaging technique with spatial resolution up to 150–350 nm. However, this technology cannot discern very small structural features, because the spatial resolution is limited by diffraction to about half of the wavelength of light (λ/2，λ is the wavelength of light). Hence, most of the developments in microscopy aim at improving resolution. In the past decades, stimulated emission depletion (STED) microscopy has been developed to bypass the diffraction limit for the application in biological imaging with resolution approaching the nanoscale. The basic principle of STED microscopy is to employ a doughnut-shape laser called the depletion laser which inhibits fluorescence emission and improves the resolution of the focal plane by depleting the peripheral fluorescence. Thereby, STED microscopy avoids the diffraction barrier and improves the spatial resolution. STED microscopy has been widely applied to address many problems in biology with both continuous wave and pulsed wave lasers. Various fluorescent nanoparticles, therefore, are attractive for far-field super-resolution microscopy. During the past decades, fluorescent nanoparticles have been used as a fluorescent label, fluorescent probe or marker for super-resolution imaging in vitro andvivo. In our study, STED microscopy is one of the breakthrough technologies that belongs to far-field optical microscopy and can reach the nanoscale spatial resolution. We demonstrate a far-field optical microscopy based on pulsed-wave lasers with the violet (405 nm) and green lasers (532 nm) for excitation and STED, respectively. Firstly,fluorescent dye - Coumarin 102 is applied to verify the stability and reliability of the STED microscopy. Then, one suitable nanoparticle is selected from three different kinds of nanoparticles (Silica Nanoparticles-NFv465, flouro-Max blue aqueous fluorescent nanoparticles, light yellow nanoparticles) based on their absorption and depletion spectrum and depletion efficiency under different depletion power. Light yellow fluorescent nanoparticles (LYs) are selected for characterizing the spatial resolution of the STED microscopy. Finally, the laser beams of the STED microscopy are utilized to scan along a glass slide, which is coated with the LYs. A two-dimensional image of the LYs pattern is established and compared with the confocal imaging, indicating that a spatial resolution (approximately 76.02 nm) has been obtained in the STED imaging so far. Even though the resolution of STED microscopy with pulsed-laser has the room to be improved, the present work shows that our lab has successfully built up the STED microscopy with the pulsed-laser

Tripropyl­ammonium trithio­cyanurate

In the title compound (systematic name: tripropyl­azanium 2,4,6-tris­ulfanyl­idene­cyclo­hexan-1-ide), (C3H7)3HN+·C3H2N3S3 −, one H atom of trithio­cyanuric acid is accepted by tripropyl­amine to form the ammonium ion. Coplanar trithio­cyanurate and tripropyl­ammonium ions [dihedral angle = 82.33 (8)°] form the salt, which is stabilised by various N—H⋯S and N—H⋯N contacts