1,721,013 research outputs found
Two new species of Calanthe (Orchidaceae; Epidendroideae) from China
No full textZhai, Jun-Wen, Chen, Li-Jun, Xing, Fu-Wu, Liu, Zhong-Jian (2013): Two new species of Calanthe (Orchidaceae; Epidendroideae) from China. Phytotaxa 123 (1): 51-55, DOI: 10.11646/phytotaxa.123.1.
FIGURE 2 in Two new species of Calanthe (Orchidaceae; Epidendroideae) from China
No full textFIGURE 2. Photos of Calanthe species. A,B. Calanthe bingtaoi. C. Calanthe graciliflora. D. Calanthe wenshanensis. E. Calanthe alismatifolia. F. Calanthe herbacea.Published as part of Zhai, Jun-Wen, Chen, Li-Jun, Xing, Fu-Wu & Liu, Zhong-Jian, 2013, Two new species of Calanthe (Orchidaceae; Epidendroideae) from China, pp. 51-55 in Phytotaxa 123 (1) on page 53, DOI: 10.11646/phytotaxa.123.1.3, http://zenodo.org/record/508501
FIGURE 3. Calanthe bingtaoi J.W.Zhai & Z.J.Liu. A in Two new species of Calanthe (Orchidaceae; Epidendroideae) from China
No full textFIGURE 3. Calanthe bingtaoi J.W.Zhai & Z.J.Liu. A. Plant of Calanthe bingtaoi. B. Flower, front view. C. Flower, side view. D. Sepals and petals. E. Labellum. F. Polinarium.Published as part of Zhai, Jun-Wen, Chen, Li-Jun, Xing, Fu-Wu & Liu, Zhong-Jian, 2013, Two new species of Calanthe (Orchidaceae; Epidendroideae) from China, pp. 51-55 in Phytotaxa 123 (1) on page 54, DOI: 10.11646/phytotaxa.123.1.3, http://zenodo.org/record/508501
FIGURE 1. Calanthe wenshanensis J.W.Zhai & Z.J.Liu. A in Two new species of Calanthe (Orchidaceae; Epidendroideae) from China
No full textFIGURE 1. Calanthe wenshanensis J.W.Zhai & Z.J.Liu. A. Plant of Calanthe wenshanensis. B. Flower, front view. C. Flower, side view. D. Longitude section of flower. E. Sepals and petals. F. Labellum. G. Pollinarium.Published as part of Zhai, Jun-Wen, Chen, Li-Jun, Xing, Fu-Wu & Liu, Zhong-Jian, 2013, Two new species of Calanthe (Orchidaceae; Epidendroideae) from China, pp. 51-55 in Phytotaxa 123 (1) on page 52, DOI: 10.11646/phytotaxa.123.1.3, http://zenodo.org/record/508501
Gibbs Sampling based Near MAP Receiver Design for Multi-User Spread Spectrum Systems
No full text在這篇論文中，我們首先架構一個統一的系統模型，分別適用於下傳同步直序分碼多工（direct-sequence code division multiple access, DS-CDMA），上傳非同步直序分碼多工，以及多載波分碼多工（multi-carrier code division multiple access, MC-CDMA）系統。接著我們會介紹幾種接近最大後機率以及最大概似的演算法，包含Gibbs抽樣方法，反覆條件最大化 (iterated conditional modes, ICM)以及期望值最大化 (expectation maximization, EM)。我們會採用這些演算法在上傳非同步DS-CDMA的接收機設計。此外，除了用戶資料的偵測，我們也會探討在盲蔽式接收機設計中，每個使用者的通道以及雜訊變異數之估測的問題。模擬的結果顯示，建構於Gibbs抽樣方法的接收機設計，其效能可以勝過ICM以及其他次佳的接收機。
基於樹狀結構搜尋之最短路徑的最佳接收機設計中，我們也提出了一個不規則樹狀結構搜尋(irregular tree search, ITS)可以進一步降低整體的複雜度。ITS可以視為一個隨機的過程去適應性地控制每一層所需保留的節點，因此在高訊號雜訊比的情況，和M-演算法相比，ITS 的複雜度能夠大幅地降低。模擬的結果顯示，在高訊號雜訊比時，無論是在效能和複雜度上，ITS都能有較好的表現。In this thesis, we first establish a unified system model for downlink synchronous direct-sequence code division multiple access (DS-CDMA), uplink asynchronous DS-CDMA, and multi-carrier CDMA (MC-CDMA) systems. Several near-maximum-a-posteriori (MAP) and near-maximum-likelihood (ML) algorithms, including Gibbs sampling, iterated conditional modes (ICM), and expectation-maximization (EM) are next introduced. These algorithms are adopted in the receiver design of uplink asynchronous direct-sequence CDMA
(DS-CDMA) system. In addition to user data estimation, channel estimation for each user and noise variance estimation for blind receiver design are also investigated. Simulation results show that the performance of the Gibbs sampling based receiver outperforms ICM and other suboptimal receivers.
Based on the tree search structure in the minimum distance optimal receiver, we also propose an irregular tree search (ITS) method to greatly reduce the overall complexity. ITS can be viewed as a stochastic procedure of adaptively controlling the survivors at each levels and thus, the complexity can be greatly reduced compared to the M-algorithm at high SNR. Simulation results show that at high SNR, ITS outperforms the M-algorithm both in error performance and complexity.Contents
1 Introduction 1
2 System Model of CDMA systems 5
2.1 MIMO System Model . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Signal Model of DS-CDMA . . . . . . . . . . . . . . . . . . . 7
2.2.1 Downlink Synchronous DS-CDMA . . . . . . . . . . . 9
2.2.2 Uplink Asynchronous DS-CDMA . . . . . . . . . . . . 12
2.3 MC-CDMA Signal Model . . . . . . . . . . . . . . . . . . . . . 14
2.3.1 OFDM System . . . . . . . . . . . . . . . . . . . . . . 15
2.3.2 Downlink Synchronous and Uplink Quasi-Synchronous
MC-CDMA . . . . . . . . . . . . . . . . . . . . . . . . 17
3 Multiuser Detection 21
3.1 Detection in CDMA Systems . . . . . . . . . . . . . . . . . . . 21
3.2 Conventional Single User Matched Filter Detector . . . . . . . 23
3.3 Optimal Multiuser Detection . . . . . . . . . . . . . . . . . . . 24
3.3.1 Optimal Receiver Design . . . . . . . . . . . . . . . . . 24
3.3.2 Complexity of the tree search algorithm . . . . . . . . 27
3.4 Sub-Optimal Multiuser Detection . . . . . . . . . . . . . . . . 28
3.4.1 Linear Multiuser Detectors . . . . . . . . . . . . . . . . 29
3.4.2 Nonlinear Multiuser Detectors . . . . . . . . . . . . . . 30
4 Near Optimal Estimation Algorithms 41
4.1 Stochastic Estimation Algorithm . . . . . . . . . . . . . . . . 42
4.1.1 Markov chain . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.2 Gibbs Sampling . . . . . . . . . . . . . . . . . . . . . . 43
4.2 Deterministic Optimization Algorithm . . . . . . . . . . . . . 47
4.2.1 The Expectation Maximization Algorithm . . . . . . . 47
4.2.2 Iterated Conditional Modes (ICM) . . . . . . . . . . . 49
5 The Near MAP Receiver Design 53
5.1 Near MAP Receiver Design with Perfect Channel Estimation . 53
5.2 Blind Near MAP Receiver Design . . . . . . . . . . . . . . . . 55
5.2.1 Derivations of Conditional Posteriori Distributions . . . 56
5.2.2 Generation of Inverse Gamma Random Variable . . . . 60
5.2.3 Interpretation of ICM receiver . . . . . . . . . . . . . . 60
5.2.4 Gibbs Sampling based blind receiver . . . . . . . . . . 61
6 Simulation Results 65
6.1 Performance of Near MAP Receiver . . . . . . . . . . . . . . . 65
6.1.1 Simulation Parameters . . . . . . . . . . . . . . . . . . 65
6.1.2 Receiver with perfect channel estimation . . . . . . . . 66
6.1.3 Blind Receiver . . . . . . . . . . . . . . . . . . . . . . . 69
6.2 Irregular Tree Search . . . . . . . . . . . . . . . . . . . . . . . 73
6.2.1 Simulation Parameters . . . . . . . . . . . . . . . . . . 74
6.2.2 Performance Evaluations . . . . . . . . . . . . . . . . . 74
7 Conclusions and Future Works 79
7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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