309,047 research outputs found
Selectivity for dimers in pentene oligomerization over acid zeolites
No full textThe reactions of 1-pentene over acid zeolites were investigated in the liquid phase at 473 K. The primary reactions were isomerization, dimerization, and subsequent cracking of dimers. Zeolites consisting of only 10-membered (MFI) or 12-membered rings (FAU, BEA) behaved similarly, with dimerization and subsequent cracking products observed. Zeolites possessing 8-membered ring pores (MOR, FER) showed very different selectivity from each other and from other zeolites. MOR showed almost complete conversion of C10 olefins, such that hexene and butene from cracking were the dominant products. FER showed high activity and selectivity for dimerization, with very small amounts of cracking products observed.Peer reviewe
More spectrum for less energy: Green cooperative sensing scheduling in CRNs
No full textDue to the increasing bandwidth demand of mobile users and their devices with energy hungry wireless networking modules, attention of research efforts has been recently shifting to find answers to the paradox of achieving more spectrum for less energy consumption. In this paper, cognitive radios have been employed to obtain more spectrum by utilizing unused licensed spectrum in an opportunistic manner. Defining the opportunity cost as the consumed energy per achieved unit of free spectrum, we propose a cooperative sensing scheduling framework to optimize the cost with the consideration of the sensing, reporting and channel switching costs in terms of energy expenditure subject to a licensed user protection threshold. In the proposed scheme, all primary channels are scheduled to be cooperatively sensed within a cycle which consists of rounds. In every round, secondary/unlicensed users (SUs) are first assigned to cooperatively sense the scheduled primary/licensed user (PU) channels. Consequently, SUs report their local sensing results to a fusion center for a global decision. Finally, SUs assigned to sense other PU channels perform channel switching for the next round. This scheme not only provides a feasible network set up in case there does not exist a sufficient number of SUs to satisfy the PU protection in a single round, but also offers an apparent reduction in the opportunity cost.</p
Multi-objective clustering optimization for multi-channel cooperative sensing in CRNs
No full textCooperative spectrum sensing (CSS) has been extensively studied in the literature to mitigate the weakness of spectrum sensing against hostile propagation phenomenon. Especially for large networks, clustered CSS is preferred to alleviate the energy efficiency, delay and overhead problems. In this study, reporting and sensing channels are first modeled with the consideration of path loss and fading. Then, CSS is divided into three phases: 1) In sensing phase, optimal sensing time is obtained for each local user subject to local detection and false alarm probability thresholds, 2) In reporting phase, adopting Dijkstra's algorithm, multi-hop paths with the maximum success rate and cluster head (CH) selection which gives the mimimum total error rate within each cluster is computed, and 3) In decision phase, collecting independent but unidentically distributed (i.u.d.) member decisions, the CH decides on channel occupancy based on an optimal voting rule for i.u.d. reports. Next, following the phases above, a multi-objective clustering optimization (MOCO) is formulated to select SUs into cluster seeking energy and throughput efficiency goals subject to global detection and false alarm probability constraints. Finally, the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is employed to solve MOCO. Results based on our approach are presented and the merits of this approach are demonstrated.</p
Green cooperative spectrum sensing and scheduling in heterogeneous cognitive radio networks
No full textIn this paper, we consider heterogeneous cognitive radio networks (CRNs) comprising primary channels (PCs) with heterogeneous characteristics and secondary users (SUs) with various sensing and reporting qualities for different PCs. We first define the opportunity as the achievable total data rate and its cost as the energy consumption caused from sensing, reporting, and channel switching operations and formulate a joint spectrum discovery and energy efficiency objective to minimize the energy spent per unit of data rate. Then, a mixed integer non-linear programming problem is formulated to determine: 1) the optimal subset of PCs to be scheduled for sensing; 2) the SU assignment set for each scheduled PC; and 3) sensing durations and detection thresholds of each SU on PCs it is assigned to sense. Thereafter, an equivalent convex framework is developed for specific instances of the above combinatorial problem. For comparison, optimal detection and sensing thresholds are also derived analytically under the homogeneity assumption. Based on these, a prioritized ordering heuristic is developed to order channels under the spectrum, energy, and spectrum-energy limited regimes. After that, a scheduling and assignment heuristic is proposed and is shown to perform very close to the exhaustive optimal solution. Finally, the behavior of the CRN is numerically analyzed under these regimes with respect to different numbers of SUs, PCs, and sensing qualities.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Sensing strategies for channel discovery in Cognitive Radio Networks
No full textWe consider spectrum sensing strategies used to discover available spectrum in Cognitive Radio Networks (CRNs), using both non-cooperative sensing and cooperative sensing approaches. After introducing the background to sensing techniques, this position paper focuses on strategies and algorithms for conducting sensing such that the sensing time and energy are minimized, and the likelihood of finding available spectrum is maximized. The paper mainly focuses on two approaches. The first is the ordering of channels to be sensed, and the second is cooperative spectrum sensing. After discussing the available strategies under each of these two approaches, we introduce our own proposed approaches. We first introduce a method for sorting the channels to be sensed in order to optimize the sensing time, while satisfying PUs' protection and false alarm constraints. Then, we introduce a framework for cooperative sensing of multiple PUs' channels by a group of SUs. The framework includes strategies for assigning different SUs to sense different PUs' channels, selection of the fusion center for each of the SUs clusters, and routing sensing data within the cluster from the SUs to the fusion center. We show how this framework is capable of optimizing different objective functions. Several open problems and future research directions are also introduced.</p
Celik Fiqh: didik hibur pendidikan islam ke arah pelaksanaan pembelajaran berpusatkan murid
No full textPermainan Celik Fiqh merupakan sebuah permainan didik
hibur yang dicipta bagi tujuan menyahut seruan
Kementerian Pendidikan Malaysia dalam pelaksanaan
pembelajaran berpusatkan murid. Permainan ini juga dapat
dijadikan bahan bantu mengajar dan aktiviti pembelajaran
kendiri bagi mata pelajaran Pendidikan Islam khususnya
bidang Feqah Tingkatan 2. Umumnya, permainan ini
berkonsepkan permainan kad yang terdiri daripada kad-kad
soalan aras rendah, sederhana dan tinggi beserta jawapan
dan kad-kad nota. Tambahan pula, permainan ini dapat
dimainkan secara fizikal dan digital. Selain itu, permainan
ini dilengkapkan lagi dengan e-infografik yang berwarna,
dan mudah difahami merangkumi semua tajuk Tingkatan 2
bidang Feqah. Gabungan antara platform fizikal dan digital
ini bertujuan untuk menyebarluaskan penggunaan
teknologi dalam pendidikan di kalangan guru dan murid.
Oleh yang demikian, permainan ini amat sesuai dijalankan
dalam kelas secara bersemuka mahupun kelas di atas
talian. Justeru, usaha mencipta permainan Celik Fiqh ini
diharapkan dapat mendedahkan kepelbagaian cara dalam
mempelajari Pendidikan Islam sekaligus menarik minat
pelajar dalam mendalami bidang Fiqh. Satu tinjauan juga
telah dijalankan terhadap beberapa orang pelajar tingkatan
2 dan guru Pendidikan Islam sebagai sampel kajian bagi
mengkaji sejauh mana keberkesanan permainan Celik
Fiqh. Hasilnya, majoriti responden daripada kaji selidik ini
berpuas hati dengan kandungan, reka grafik dan aturan
permainan Celik Fiqh
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Revision des kontrafaktischen Erzählens. Michael Navratil zeigt das politische Potenzial kontrafaktischer Gegenwartsliteratur auf
No full textCelik N. Revision des kontrafaktischen Erzählens. Michael Navratil zeigt das politische Potenzial kontrafaktischer Gegenwartsliteratur auf. DIEGESIS. Interdisziplinäres E-Journal für Erzählforschung/Interdiscipli-nary E-Journal for Narrative Research. 2023;12(1):98-104
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