1,720,956 research outputs found
Interference Alignment and Cancellation
Get PDFThe throughput of existing MIMO LANs is limited by the number of antennas on the AP. This paper shows how to overcome this limit. It presents interference alignment and cancellation (IAC), a new approach for decoding concurrent sender-receiver pairs in MIMO networks. IAC synthesizes two signal processing techniques, interference alignment and interference cancellation, showing that the combination applies to scenarios where neither interference alignment nor cancellation applies alone. We show analytically that IAC almost doubles the throughput of MIMO LANs. We also implement IAC in GNU-Radio, and experimentally demonstrate that for 2x2 MIMO LANs, IAC increases the average throughput by 1.5x on the downlink and 2x on the uplink.United States. Defense Advanced Research Projects Agency. Information Theory for Mobile Ad-Hoc Networks Progra
An integrated CRISPR-Cas toolkit for engineering human cells
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 145-158).Natively functioning Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated (Cas) system is a prokaryotic adaptive immune system that confers resistance to foreign genetic elements including plasmids and phages. Very recently, a two-component CRISPR-Cas technology from Streptococcus Pyogenes comprising of the RNA-guided DNA endonuclease Cas9 and the guide RNA (gRNA) has been demonstrated to enable unprecedented genome editing efficiency across all domains of life. Current applications however, employ CRISPR/Cas technology in a stand-alone fashion, isolated from the rich biological machinery of the host environment in which it is applied. In this thesis, I present a toolkit designed by integrating CRISPR/Cas technology with a wide array of mammalian molecular components, thereby enabling altogether novel applications while enhancing the efficiency of current applications. By integrating a catalytically dead version of the CRISPR/Cas protein Cas9 (dCas9) with mammalian transcriptional activator VP64 and mammalian transcriptional repressor KRAB, we build and characterize tunable, multifunctional and orthogonal CRISPR/Cas transcription factors (CRISPR-TFs) in human cells. By integrating CRISPR-TFs and Cas6/Csy4 based RNA processing with multiple mammalian RNA regulatory strategies including RNA Polymerase II (RNAP II) promoters, RNAtriple- helix structures, introns, microRNAs and ribozymes, we demonstrate efficient modulation of endogenous promoters and the implementation of tunable synthetic circuits such as multistage cascades and RNA-dependent networks that can be rewired with Csy4. In summary, our integrated toolkit enables efficient and multiplexed modulation of endogenous gene networks, construction of highly scalable and tunable synthetic gene circuits. Our toolkit can be used for perturbing endogenous networks towards developmental, therapeutic and synthetic biology applications.by Samuel David Perli.Ph. D
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Designing interference-free wireless links using LCD-camera pairs
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010."June 2010." Cataloged from PDF version of thesis.Includes bibliographical references (p. 61-63).Given the abundance of cameras and LCDs in today's environment, there exists an untapped opportunity for using these devices for communication. Specifically, cameras can tune to nearby LCDs and use them for network access. The key feature of these LCD-camera links is that they are highly directional and hence enable a form of interference-free wireless communication. This makes them an attractive technology for dense, high contention scenarios. The main challenge however, to enable such LCD-camera links is to maximize coverage, that is to deliver multiple Mb/s over multi-meter distances, independent of the view angle. To do so, these links need to address unique types of channel distortions such as perspective distortion and blur. This thesis explores this novel communication medium and presents PixNet, a system for transmitting information over LCD-camera links. PixNet generalizes the popular OFDM transmission algorithms to address the unique characteristics of the LCD-Camera links which include perspective distortion, blur and sensitivity to ambient light. We built a prototype of PixNet using off-the-shelf LCDs and cameras. An extensive evaluation shows that a single PixNet link delivers data rates of up to 12 Mb/s at a distance of 10 meters, and works with view angles as wide as 120.by Samuel David Perli.S.M
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Tunable and Multifunctional Eukaryotic Transcription Factors Based on CRISPR/Cas
Get PDFTranscriptional regulation is central to the complex behavior of natural biological systems and synthetic gene circuits. Platforms for the scalable, tunable, and simple modulation of transcription would enable new abilities to study natural systems and implement artificial capabilities in living cells. Previous approaches to synthetic transcriptional regulation have relied on engineering DNA-binding proteins, which necessitate multistep processes for construction and optimization of function. Here, we show that the CRISPR/Cas system of Streptococcus pyogenes can be programmed to direct both activation and repression to natural and artificial eukaryotic promoters through the simple engineering of guide RNAs with base-pairing complementarity to target DNA sites. We demonstrate that the activity of CRISPR-based transcription factors (crisprTFs) can be tuned by directing multiple crisprTFs to different positions in natural promoters and by arraying multiple crisprTF-binding sites in the context of synthetic promoters in yeast and human cells. Furthermore, externally controllable regulatory modules can be engineered by layering gRNAs with small molecule-responsive proteins. Additionally, single nucleotide substitutions within promoters are sufficient to render them orthogonal with respect to the same gRNA-guided crisprTF. We envision that CRISPR-based eukaryotic gene regulation will enable the facile construction of scalable synthetic gene circuits and open up new approaches for mapping natural gene networks and their effects on complex cellular phenotypes.United States. Defense Advanced Research Projects AgencyNational Institutes of Health (U.S.) (New Innovator Award 1DP2OD008435)National Science Foundation (U.S.) (1124247
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