101 research outputs found
Spectrum Sensing Mechanisms in Cognitive Radio Based LTE Femtocells
No full textThe ever-increasing demand for wireless technology has rendered the spectrum a restricted resource. This chapter provides an insight into fundamental signal processing used for spectrum sensing and explores the conventional spectrum sensing techniques used in cognitive radio (CR) networks. It investigates different models and statistics used for performance analysis of these schemes and presents the state-of-the-art research results, which outline the widely used models and statistics for specific sensing techniques. The chapter presents a comparison of the conventional spectrum sensing techniques used by CRs. The Long Term Evolution (LTE) cognitive femtocells have CR capabilities of sensing the spectrum and preventing interference by proper allocation of the spectrum. History assisted energy efficient spectrum sensing is well suited to infrastructure CR networks and employs a processing database. The chapter shows the classification of spectrum sensing techniques based on models and statistics implemented.<br/
Robust, scalable, and practical algorithms for recommender systems
No full textThe purpose of recommender systems is to filter information unseen by a user to predict whether a user would like a given item. Making effective recommendations from a domain consisting of millions of ratings is a major research challenge in the application of machine learning and data mining. A number of approaches have been proposed to solvethe recommendation problem, where the main motivation is to increase the accuracy of the recommendations while ignoring other design objectives such as scalability, sparsity and imbalanced dataset problems, cold-start problems, and long tail problems. The aim of this thesis is to develop recommendation algorithms that satisfy the aforementioned design objectives making the recommendation generation techniques applicable to a wider range of practical situations and real-world scenarios.With this in mind, in the first half of the thesis, we propose novel hybrid recommendation algorithms that give accurate results and eliminate some of the known problems with recommender systems. More specifically, we propose a novel switching hybrid recommendation framework that combines Collaborative Filtering (CF) with a content-based filtering algorithm. Our experiments show that the performance of our algorithm is better than (or comparable to) the other hybrid recommendation approaches available in the literature. While reducing the dimensions of the dataset by Singular Value Decomposition (SVD), prior to applying CF, we discover that the SVD-based CF fails to produce reliable recommendations for some datasets. After further investigation, we find out that the SVD-based recommendations depend on the imputation methods used to approximate the missing values in the user-item rating matrix. We propose various missing value imputation methods, which exhibit much superior accuracy and performance compared to the traditional missing value imputation method - item average. Furthermore, we show how the gray-sheep users problem associated with a recommender system can effectively be solved using the K-means clustering algorithm. After analysing the effect of different centroid selection approaches and distance measures in the K-means clustering algorithm, we demonstrate how the gray-sheep users in a recommender system can be identified by treating them as an outlier problem. We demonstrate that the performance (accuracy and coverage) of the CF-based algorithms suffers in the case of gray-sheep users. We propose a hybrid recommendation algorithm to solve the gray-sheep users problem.In the second half of the thesis, we propose a new class of kernel mapping recommender system methods that we call KMR for solving the recommendation problem. The proposed methods find the multi-linear mapping between two vector spaces based on the structure-learning technique. We propose the user- and item-based versions of the KMR algorithms and offer various ways to combine them. We report results of an extensive evaluation conducted on five different datasets under various recommendation conditions. Our empirical study shows that the proposed algorithms offer a state-of-the-art performance and provide robust performance under all conditions. Furthermore, our algorithms are quite flexible as they can incorporate more information|ratings, demographics, features, and contextual information|easily into the forms of kernels and moreover, these kernels can be added/multiplied. We then adapt the KMR algorithm to incorporate new data incrementally. We offer a new heuristic namely KMRincr that can build the model without retraining the whole model from scratch when new data are added to the recommender system, providing significant computation savings. Our final contribution involves adapting the KMR algorithms to build the model on-line. More specifically, we propose a perceptron-type algorithm namely KMR percept which is a novel, fast, on-line algorithm for building the model that maintains good accuracy and scales well with the data. We provide the temporal analysis of the KMR percept algorithm. The empirical results reveal that the performance of the KMR percept is comparable to the KMR, and furthermore, it overcomes some of the conventional problems with recommender systems
Novel Heuristics for Coalition Structure Generation in Multi-Agent Systems
No full textA coalition is a set of self-interested agents that agree to cooperate for achieving a set of goals. Coalition formation is an active area of research in multi-agent systems nowadays. Central to this endeavour is the problem of determining which of the many possible coalitions to form in order to achieve some goal, which is called coalition structure generation. Coalition structure generation problem is extremely challenging due to the number of possible solutions that need to be examined, which grows exponentially with the number of agents involved. Generally, agents would enumerate all possible coalitions, store them in memory, and then try to construct the coalition structure that maximizes the sum of the values of the coalitions. However, this is not feasible when we have a large number of agents, and other constraints on execution time, and memory. Hence, there is a need to develop an algorithm that can generate solutions rapidly for large number of agents while providing bounds on the value of solution as well. With this in mind, we propose two new heuristics, namely LocalSearch and GreedySearch, for generating the coalition structure, which satisfy these properties. We empirically show that these heuristics are able to return ‘good-enough’ solutions in very short time. Furthermore, they enhance the performance of state of the art algorithm, IP (proposed by [12]) in terms of increased lower bound, anytime property, and solution quality. Furthermore, we implemented different heuristics for selecting a sub-space in the IP algorithm and show how the time required to find a good-enough solution depends on the selection of a sub-space in the IP algorithm
Comparative Analysis of Flame Propagation and Flammability Limits of CH4/H2/Air Mixture with or without Nanosecond Plasma Discharges
Get PDFThis study investigates the kinetic modeling of CH4/H2/Air mixture with nanosecond pulse discharge (NSPD) by varying H2/CH4 ratios from 0 to 20% at ambient pressure and temperature. A validated version of the plasma and chemical kinetic mechanisms was used. Two numerical tools, ZDPlasKin and CHEMKIN, were combined to analyze the thermal and kinetic effects of NSPD on flame speed enhancement. The addition of H2 and plasma excitation increased flame speed. The highest improvement (35%) was seen with 20% H2 and 1.2 mJ plasma energy input at ϕ = 1. Without plasma discharge, a 20% H2 blend only improved flame speed by 14% compared to 100% CH4. The study found that lean conditions at low flame temperature resulted in significant improvement in flame speed. With 20% H2 and NSPD, flame speed reached 37 cm/s at flame temperature of 2040 K at ϕ = 0.8. Similar results were observed with 0% and 5% H2 and a flame temperature of 2200 K at ϕ = 1. Lowering the flame temperature reduced NOx emissions. Combining 20% H2 and NSPD also increased the flammability limit to ϕ = 0.35 at a flame temperature of 1350 K, allowing for self-sustained combustion even at low temperatures
Novel centroid selection approaches for KMeans-clustering based recommender systems
No full textRecommender systems have the ability to filter unseen information for predicting whether a particular user would prefer a given item when making a choice. Over the years, this process has been dependent on robust applications of data mining and machine learning techniques, which are known to have scalability issues when being applied for recommender systems. In this paper, we propose a k-means clustering-based recommendation algorithm, which addresses the scalability issues associated with traditional recommender systems. An issue with traditional k-means clustering algorithms is that they choose the initial k centroid randomly, which leads to inaccurate recommendations and increased cost for offline training of clusters. The work in this paper highlights how centroid selection in k-means based recommender systems can improve performance as well as being cost saving. The proposed centroid selection method has the ability to exploit underlying data correlation structures, which has been proven to exhibit superior accuracy and performance in comparison to the traditional centroid selection strategies, which choose centroids randomly. The proposed approach has been validated with an extensive set of experiments based on five different datasets (from movies, books, and music domain). These experiments prove that the proposed approach provides a better quality cluster and converges quicker than existing approaches, which in turn improves accuracy of the recommendation provided
Ziziphora clinopodioides subsp. filicaulis Rechinger 1982
No full text<p> <i>Ziziphora clinopodioides</i> subsp. <i>filicaulis</i> (Rechinger) Rechinger (1982: 486). (Fig. 8).</p> <p> ≡ <i>Ziziphora filicaulis</i> Rechinger (1951: 167).</p> <p> <b>Type:</b> — IRAN. Shahrud-Bustam. In saxosis et glareosis calc. declivium australium Shahvar, 3500‒3900 m, 25 July 1948, <i>Rechinger</i> 6014! (holotype W19560006986!, isotypes B100241841!, BM000950423!, G00402138!, G00402139!, K000247829!, S-G-6502-photo!, US 00121718-photo!).</p> <p>Suffruticose-caespitose, with sterile filamentous shoots creeping between fragments of stones, with slender slanted or ascending flowering stems, 2‒4 cm, green to purplish, glabrescent to short hairy. Leaves 3‒7 × 2‒4 mm long, broadly ovate to ovate-orbicular, glabrous or sparsely papillose-hirsute, sparsely to minutely glandular-dotted. Capitula globose. Calyx ± 5 mm long, mostly purple, densely long whitish hairy.</p> <p> <b>Habitat:—</b> Steppes, metamorphic and calcareous rocks; elev.. 2200 m; fl. & fr. May to August.</p> <p> <b>Distribution:</b> —Eastern Turkey, Iran.</p> <p>This subspecies which is a new record for Turkey is easily distinguished from the other subspecies distributed in Turkey mentioned here, in its dense and long white hairs on the calyx (Fig. 8).</p> <p> <b>Examined Specimens:</b> — TURKEY. Van: Özalp, 2200 m, 27 May 1966, <i>J</i> <i>.</i> <i>Eiselt</i> s.n. (W19660021341).</p>Published as part of <i>Dirmenci, Tuncay, Haloob, Ali, Celep, Ferhat & Ghazanfar, Shahina A., 2023, Contributions to Ziziphora clinopodioides (Lamiaceae) in Turkey and Iraq, pp. 279-293 in Phytotaxa 592 (3)</i> on pages 289-290, DOI: 10.11646/phytotaxa.592.3.6, <a href="http://zenodo.org/record/7850554">http://zenodo.org/record/7850554</a>
Facile synthesis of CTAB coated Au-Ag core-shell nanoparticles and their catalytic and antibacterial activity
No full textThis work reports the synthesis of cationic surfactant-coated Au-Ag core-shell (Au@Ag) nanoparticles (NPs) via a straightforward seed-mediated approach. The UV-Vis analysis showed that the plasmon peak position of synthesized Au@Ag NPs correlated with the thickness of the Ag shell encapsulating the Au core. The Au@Ag NPs have shown impressive catalytic performance for the reduction reactions of 4-nitrophenol (4-NP) and methyl orange (MO) where the apparent rate constant experienced a remarkable increase by 67-fold and 90-fold, respectively, when Au@Ag NPs with the Ag-shell thickness of 6.3 nm were employed as a catalyst, compared to Au NPs. This multifold improvement in the activity cannot be simply accounted for by the increase in surface area of NPs and is attributed to the electronic synergistic effects between Au and Ag in the core-shell NPs. Furthermore, while Au@Ag NPs exhibited heightened antibacterial activity against both Gram-positive S. aureus and Gram-negative E. coli bacteria, this enhancement is modest. Notably, the anticipated significant enhancement attributed to Ag's renowned antibacterial properties was not observed. The presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) enables both Au and Au@Ag NPs to effectively bind with the negatively charged bacterial cell membranes through electrostatic interactions. Apparently, CTAB enables both types of NPs to effectively target and eliminate bacteria with comparable efficiency.</p
Ziziphora clinopodioides subsp. ronnigeri Rechinger 1982
No full textZiziphora clinopodioides subsp. ronnigeri (Nábělek) Rechinger (1982: 485) (Fig. 7). Ziziphora ronnigeri Nábělek (1926: 46) Type: — TURKEY. Van: Ad pagum Gurundast, inter Sattak (Çatak) et Wan (Van), ad rupes schistosas. 1800 m, 01 August 1910, Nábělek 1476 (lectotype SAV0002377 -photo!; isolectotype SAV0002376 -photo!; here designated by Dirmenci). Stems erect or ascending, up to 30 cm tall, branched or not, green to pale-green, short pubescent with glandular puberulent and sessile glands. Leaves sometimes fasciculate; lanceolate to broadly elliptic, 15‒25 × 2‒6(‒8) mm, attenuate at base, acute to obtuse at apex, subglabrous to finely puberulous with sessile glands on both surfaces, ciliate at margins. Inflorescence capitate. Calyx 6‒7 mm long, green to whitish green, short pubescent to with long spreading white hairs and sessile glands. Habitat: —Mountain steppes, schist cliffs, limestone; elev.. 1600‒2400 m; fl. & fr. July to August. Distribution: —East and southeast of Turkey and West Iran. It is not clear if this taxon dwells also in Iraq, there are no records in the country but it might be eventually found there. Examined Specimens: — TURKEY. Erzurum: Karakaya dag, Agviran, N of Hınıs, 2250 m, Watson 3671 (K!); Ağrı: E side of Tahir pass, 19 km from Eleşkirt to Horasan, 2400 m, 24. July 1966, Davis 47094 (K!); Ibid, 04 August 1962, Furse 3614 (K!); Ibidem, 25.08.1966, Archibald 3230 (K!); Ağrı: 8 km from Akçay to Cumaçay, 1650 m, 17.July.1966, Davis 46795 (K!); Suluçem, S of Balık lake, 2300 m, 23 July1966, Davis 47271 (K!); Kars: 7 km from Karakurt to Sarıkamış, 1780 m, 14 July1966, Davis 46481 (K!); Bitlis: Center of the Nemrut Dağ, 2400 m, 11 August 1956, McNeil 540 (K!); Van: Edremit-Gevaş, 2000 m, 13 July1954, Davis 22659 & Polunin (BM!); Artos Dag, above Gevaş, 2133 m, limestone gorge, 14 July1954, Davis 22702 (BM!, K!); Erek Dağ, 1981 m, 18 July 1954, Davis 22967 & Polunin (BM!); 26 km from Başkale to Hoşap, 2400 m, 03 July 1966, Davis 45889 (K!); Hakkari: Karadağ, 2743 m, 15 August1954, Davis 24366 & Polunin (BM!). Ziziphora ronnigeri was described by Nábělek in 1926 from specimens collected from southeastern Turkey. Rechinger in Flora Iranica (1982) evaluated it as a subspecies of Ziziphora clinopodioides and stated that the type specimen was in BRA. However, the specimens that Nábělek collected during his “Iter Turcico-Persicum” trip between 1909‒1910 were transferred to the SAV herbarium. All of Nábělek’s collections (years 1909‒1910) can be seen from the virtual herbarium (http://www.nabelek.sav.sk/). There are two specimens numbered Nábělek 1476 (photo!), which is the type specimen of subsp. ronnigeri at SAV. Between these specimens, the specimen with the barcode SAV0002377 was designated as the lectotype (Fig. 7), as it is the best-preserved specimen that clearly represents the characteristics of the taxon in the protologue, and the specimen with the barcode SAV0002376 is designated as the isolectotype.Published as part of Dirmenci, Tuncay, Haloob, Ali, Celep, Ferhat & Ghazanfar, Shahina A., 2023, Contributions to Ziziphora clinopodioides (Lamiaceae) in Turkey and Iraq, pp. 279-293 in Phytotaxa 592 (3) on page 287, DOI: 10.11646/phytotaxa.592.3.6, http://zenodo.org/record/785055
Ziziphora clinopodioides subsp. brevistamina A. Haloob 2023, subsp. nov.
No full textZiziphora clinopodioides subsp. brevistamina A.Haloob, subsp. nov. (Figs. 2 & 3). Type:— IRAQ. S. Pir Omar Gudrun, mountainside, 2000 m, 6 June 1948, A.Rawi 12031 (holotype BAG!). (Fig. 3). Diagnosis: —Affinis subsp. kurdica (Rech.f.) Rech. f. sed foliis ovato-orbiculatis, calyce minus quam 4.5 mm longo, staminibus a corollae fauces non exsertis, stylo staminibus longiore differt (Figs. 2A–E) Description: —Stem ascending or decumbent, 15‒20 cm tall, branched from base and upper half, densely pubescent-villous with white eglandular hairs. Leaves ovate-suborbicular or lanceolate, 4‒10 × 4‒7 mm, base rounded, apex acute or obtuse, pubescent with white eglandular hairs and sessile yellow glands; petiole c. 1 mm long. Inflorescences in a dense terminal head, verticillasters many-flowered; bracts petiolate, ovate-lanceolate, 3‒7 × 1‒4 mm; bracteoles minute, subulate-linear, 1‒2 mm long; pedicel c. 1 mm long. Calyx slightly bilabiate, tubular, 4‒4.5 mm long, 13-veined, green-whitish, throat hairy, upper lip 3-toothed, 1 mm long, subequaling 2-toothed lower lip, slightly dense white pubescent-hirsute outside with eglandular hairs and sessile yellow glands. Corolla c. 7 mm long, creamy-white with purple dots on lower lip (in dry specimens), with sessile yellow glands on outside of lips. Stamens not exserted from corolla throat, the anterior pair fertile, not coherent laterally, the posterior stamens absent. Style longer than stamens. Ziziphora clinopodioides subsp. brevistamina is easily distinguished from other Z. clinopodioides subspecies in its short stamens not exserted from the corolla throat. Morphologically the new subspecies resembles subsp. kurdica (Rechinger 1951: 167) Rechinger (1982: 487), including the ascending or decumbent stem and slightly dense white pubescent-hirsute eglandular hairs outside the calyx; but it differs in its ovate to suborbicular or lanceolate leaves, calyx 4‒4.5 mm long, and stamens not exserted from corolla throat (subsp. kurdica has ovate or elliptic-lanceolate to ovate-lanceolate leaves, calyx 5‒6 mm long, and the stamens exserted from corolla throat). It differs in the indumentum of calyx and longer stems from subsp. elbursensis (Rechinger 1951: 169) Rechinger (1982: 487). The new subspecies is different from subsp. rigida (Boissier 1879: 586) Rechinger (198: 483), subsp. szowitsii (Rechinger 1951: 166) Rechinger (1982: 484) and subsp. ronnigeri (Nábĕlek (1926: 46)) Rechinger (1982: 485) in its ascending or decumbent stems. From subsp. pseudodasyantha (Rechinger 1951: 167) Rechinger (1982: 485) and subsp. filicaulis (Rechinger 1951: 167) Rechinger (1982: 486) by its short and slightly dense calyx hairs, and from subsp. afghanica (Rechinger 1951: 169) Rechinger (1982: 488) and subsp. bungeana (Juzepczuk 1954: 664) Rechinger (1982: 487) by its ovate-suborbicular leaves, short pedicel (c. 1 mm long) and, calyx 4‒4.5 mm long. Habitat: —Mountain sides; elev. 1800‒2000 m; fl. & fr. June to July. Disitribution: —It is an endemic plant to northern Iraq (Fig. 4). Very rare, found twice in one location in the southern sector of the thorn-cushion zone of Iraq. Examined specimens: — IRAQ. MSU: S. Pir Omar Gudrun, mountainside, 2000 m, 6 June 1948, A. Rawi 12031 (BAG!); Pir Omar Gudrun, 1800 m, 7 June 1948, A.Rawi 12087 (Paratype, BAG!). Rawi noted the Kurdish name GIAPAPULA or NA’NA’ on the sepecimen labels (Kurd., Pir Omar Gudrun, A.Rawi 12031 & 12087).Published as part of Dirmenci, Tuncay, Haloob, Ali, Celep, Ferhat & Ghazanfar, Shahina A., 2023, Contributions to Ziziphora clinopodioides (Lamiaceae) in Turkey and Iraq, pp. 279-293 in Phytotaxa 592 (3) on pages 282-284, DOI: 10.11646/phytotaxa.592.3.6, http://zenodo.org/record/785055
Saxifraga sibirica Linnaeus 1762
No full textSaxifraga sibirica Linnaeus, Species Plantarum, ed. 2, 1: 577. 1762. "Habitat in Sibiria." RCN: 3168. Lectotype (Ghazanfar in Nasir & Ali, Fl. W Pakistan 108: 12. 1977): Herb. Linn. No. 575.49 (LINN). Current name: Saxifraga sibirica L. (Saxifragaceae). Note: See additional notes by Webb (in Bot. J. Linn. Soc. 95: 266. 1987).Published as part of Jarvis, Charlie, 2007, Chapter 7: Linnaean Plant Names and their Types (part S), pp. 806-877 in Order out of Chaos. Linnaean Plant Types and their Types, London :Linnaean Society of London in association with the Natural History Museum on page 822, DOI: 10.5281/zenodo.29197
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