bluuebunny/crossref_metadata_2025 huggingface dataset:
Germplasm diversity and differentiation ofHelianthus tuberosusL. revealed by AFLP marker and phenotypic traits
Authors: KOU Y. X. , ZENG J. , LIU J. Q. , ZHAO C. M.
Published: August 2013

Helianthus tuberosusL. is regarded as one of the most important bioenergy crops because of its tolerance to arid conditions and its high biomass production. Future breeding programmes will rely on the available germplasm, thus necessitating a critical assessment of genetic diversity and differentiation in the species. The germplasm diversity and regional differentiation ofH. tuberosusL. was assessed for 60 accessions collected from East Asia and Europe by means of amplified fragment length polymorphisms (AFLPs), phenotypic traits and chemical analysis. The analysis did not reveal separate clusters for accessions from East Asia and Europe, with 5% for genetic and 0·27% for phenotypic variability, although some regional accessions were closely related to each other with respect to morphological, chemical and genetic variation. Both phenotypic and genetic relationships showed a moderate correlation with colour of tubers, which can be used as an important criterion for germplasm management of the crop. Three major genetic groups were identified from the accessions. Within the groups derived from the genetic data, both morphological and chemical traits were very variable. The most important features of Groups I, II and III were: Group I, strong sexual reproduction, higher above-ground biomass and nutrient content; Group II, longer vegetative growth; Group III, higher tuber yield and total sugar content. High diversity was found in both European and East Asian accessions as well as within each genetic group, suggesting that there is a strong base for future breeding from these plants.
Do Overvaluation-Driven Stock Acquisitions Really Benefit Acquirer Shareholders?
Authors: Akbulut Mehmet E.
Published: August 2013

I study the effects of overvalued equity on acquisition activity and shareholder wealth, using managers’ insider trades to measure overvaluation. I find that overvalued equity drives managers to make stock acquisitions, and such acquisitions destroy value for acquirer shareholders. Overvalued stock acquirers earn negative and lower returns in the short run and substantially underperform similarly overvalued nonacquirer firms in the long run. My results do not support the idea that managers can benefit shareholders by converting overvalued equity into real assets through stock acquisitions.
Feeding ecology of the southern thorny skate,Amblyraja doellojuradoion the Argentine Continental Shelf
Authors: Delpiani G.E. , Spath M.C. , Figueroa D.E.
Published: August 2013

The feeding ecology of the southern thorny skate,Amblyraja doellojuradoi, on the Argentine Continental Shelf was evaluated using generalized linear models.Amblyraja doellojuradoipreyed mainly on crabs (85.41% index of relative importance (IRI)) and to a lesser extent on polychaetes (4.98% IRI), teleosts (3.28% IRI), isopods (2.03% IRI), other crustaceans (1.52% IRI) and other invertebrates (2.78% IRI). As individuals increased in size, the consumption of crabs also increased and the consumption of polychaetes and other invertebrates decreased. The study area was divided into a northern (36°–43°S) and a southern (43°–50°S) region. Regarding the latitude of capture, it was observed thatA. doellojuradoimainly fed on crabs in the north and on fish, isopods and other crustaceans in the south. Females ofA. doellojuradoihad a stronger preference for fish and isopods than males. As to sexual maturity, immatures fed more on polychaetes and other crustaceans than did mature. The ontogenetic change in feeding habits could be attributed to body size and an increasing ability to capture larger prey, rather than to food availability. However, this point cannot be confirmed because little is known about the benthic fauna of this area.
The UFW and the Undocumented
Authors: Bardacke Frank
Published: August 2013

It has become an embarrassment. The American Conservative crows, “Cesar Chávez, Minuteman,” and the accompanying article delivers the news that the United Farm Workers was not only anti-immigrant but that it set up its own border patrol between Arizona and Mexico. The magazine does not stand alone. Leaders of current right-wing vigilante groups claim Chávez's retroactive endorsement for their occasional attempts to close small sections of the border. In response, Chávez's defenders contend that the UFW opposed the undocumented only when they broke strikes; and besides, that was long ago, and now the union is a strong defender of immigrant rights. Thus, UFW policy toward the undocumented—controversial in its own time—once again has become a subject of public debate, threatening to tarnish the name given to so many California streets, parks, schools, community centers, and even university departments.
Shantytown Dwellers' Resistance in Brazil's First Republic (1890–1930): Fighting for the Right of the Poor to Reside in the City of Rio de Janeiro
Authors: Mattos Romulo Costa
Published: August 2013

This work analyzes evidence of the resistance of poor shantytown dwellers during Brazil's First Republic period (1889–1930), which corresponds to the emergence and consolidation of these favela settlements into the city of Rio de Janeiro. This text not only addresses the different forms of resistance practiced by shantytown residents during the attempts by the government to demolish their homes, but also pays special attention to the years between 1907 and 1927 when the people of Morro da Favela (currently Morro da Providência) ensured the permanence of their houses through street protests.
Beacon selection and calibration for the efficient localization of a mobile robot
Authors: Park Jaehyun , Lee Jangmyung
Published: August 2013

This paper proposes a localization scheme using ultrasonic beacons in an unstructured multi-block workspace. Indoor localization schemes using ultrasonic sensors have widely been studied due to their low costs and high accuracies. However, ultrasonic sensors are susceptible to environmental noise due to the propagation characteristics of ultrasonic waves. In addition, the decay of ultrasonic signals over long distances implies that ultrasonic sensors are unsuitable for use in large indoor environments. To overcome these shortcomings of ultrasonic sensors, while retaining their advantages, a multi-block approach was devised by dividing an indoor space into several blocks with multiple beacons in each block. However, it is difficult to divide an indoor space into several blocks when beacons cannot be installed in a regular manner or when some new beacons are installed. To resolve this difficulty, a dynamic algorithm is needed to divide an indoor space into multiple blocks and to select suitable beacons. Therefore, this paper proposes a real-time localization scheme to estimate the position of a mobile robot independent of beacon locations and to estimate the position of a new beacon installed at an unknown position. A beacon selection algorithm was developed to select optimal beacons according to robot position and to set up sets of beacons for mobile robot navigation. By using the new beacon searching and calibration algorithm, a mobile robot is able to navigate in an unknown space without requiring the additional setup time needed to install new beacons. The performance of the proposed localization system was verified using real experiments.
Against the clock: time awareness in early modern Antwerp, 1585–1789
Authors: BLONDÉ BRUNO , VERHOEVEN GERRIT
Published: August 2013

Traditionally a large role has been attributed to the spread of clocks and watches in fostering a ‘modern’ awareness of time. Yet, little research is available that empirically enables signs of growing time awareness to be linked to the distribution of time-keeping devices. In this article both these phenomena are brought together using two independent sets of evidence that permit the hypothesis that clocks and watches contributed to a heightened consciousness of time to be tested. While the ownership of clocks and watches was socially skewed, highly gendered and unevenly distributed over time, time awareness – as exemplified throughout numerous court cases – was essentially none of these.
Development of face discrimination abilities, and relationship to magnocellular pathway development, between childhood and adulthood
Authors: PALLETT PAMELA M. , DOBKINS KAREN R.
Published: August 2013

The current study tested the development of face and object processing in young children (mean age = 5.24 years), adolescents (mean age = 15.8 years), and adults (mean age = 21.1 years) using stimuli that were equated for low-level visual characteristics (luminance, contrast, and spatial frequency make-up) and methods that equate for difficulty across ages. We also tested sensitivity to luminance and chromatic contrast (i.e., thought to be mediated primarily by the subcortical Magnocellular (M) and Parvocellular (P) pathways, respectively) to determine whether age-related improvements in face or object discrimination were driven by age-related changes in the M and/or P pathways. Results showed a selective age-related improvement in face sensitivity and a relationship between age-related increases in face sensitivity and luminance contrast sensitivity. These results add to the mounting evidence that the M pathway may influence face processing.
Learning the identity effect as an artificial language: bias and generalisation
Authors: Gallagher Gillian
Published: August 2013

The results of two artificial grammar experiments show that individuals learn a distinction between identical and non-identical consonant pairs better than an arbitrary distinction, and that they generalise the distinction to novel segmental pairs. These results have implications for inductive models of learning, because they necessitate an explicit representation of identity. While identity has previously been represented as root-node sharing in autosegmental representations (Goldsmith 1976, McCarthy 1986), or implicitly assumed to be a property that constraints can reference (MacEachern 1999, Coetzee & Pater 2008), the model of inductive learning proposed by Hayes & Wilson (2008) assumes strictly feature-based representations, and is unable to reference identity directly. This paper explores the predictions of the Hayes & Wilson model and compares it to a modification of the model where identity is represented (Colavinet al.2010). The results of both experiments support a model incorporating direct reference to identity.
Laryngeal co-occurrence restrictions in Aymara: contrastive representations and constraint interaction
Authors: Mackenzie Sara
Published: August 2013

Through analyses of laryngeal co-occurrence restrictions in two varieties of Aymara, this article shows that contrastively specified representations are crucial in shaping phonological patterning. The article argues for a model of contrastive specifications in which features are hierarchically ordered (Dresher 2009). This results in asymmetries between features such that, for a given inventory, some features are contrastively specified in a greater number of segments than others. This asymmetry between features plays a central role in accounting for the interaction of place of articulation features and laryngeal features in Bolivian Aymara. The article also demonstrates that contrastive representations can be achieved as output forms in Optimality Theory and that the constraints which determine contrastive representations can be integrated with constraints which motivate restrictions on the co-occurrence, ordering and location of laryngeal features in Peruvian and Bolivian Aymara.
Stress processing in Mandarin and Korean second language learners of English
Authors: LIN CANDISE Y. , WANG MIN , IDSARDI WILLIAM J. , XU YI
Published: August 2013

This study examined stress processing among Mandarin and Korean second language learners of English and English monolinguals. While both English and Mandarin have contrastive stress at the word-level, Korean does not. Consequently, Mandarin speakers may have an advantage over Korean speakers in English stress processing, even when matched for their general English proficiency. Experiment 1 assessed participants’ stress encoding ability for nonwords in a short-term memory task. Experiment 2 examined the effect of stress in online word recognition in a lexical decision task by manipulating word frequency, stress location, and vowel quality. The results of both experiments support an advantage for English and Mandarin speakers over Korean speakers in stress processing of real words and nonwords. Only Korean speakers’ lexical judgment of nonwords was modulated by word frequency, suggesting that they do not utilize stress in lexical access. Only English speakers’ word recognition was facilitated by vowel quality changes. These results suggest that the abilities of non-native speakers to process stress in their L2 is influenced by the characteristics of the stress systems in their L1.
Fast-food consumers in Singapore: demographic profile, diet quality and weight status
Authors: Whitton Clare , Ma Yi , Bastian Amber Carla , Fen Chan Mei , Chew Ling
Published: August 2013

Objective

To determine the demographic profile of fast-food consumers among adult Singapore residents and ascertain whether fast-food consumption frequency is associated with diet quality and weight status.

Design

A nationally representative cross-sectional survey including an FFQ and anthropometric measures. Participants were grouped based on their fast-food consumption frequency as non-consumer, occasional consumer or regular consumer, with regular defined as at least once per week.

Setting

Individuals living in the community in Singapore.

Subjects

Singapore residents (n1627) aged 18–69 years of Chinese, Malay and Indian ethnicity.

Results

Proportions of regular fast-food consumers were higher in younger age groups, higher income groups and middle education level groups. Mean daily energy intake was positively associated with fast-food consumption frequency (non-consumers 9636 kJ (2303 kcal); occasional consumers 11 159 kJ (2667 kcal); regular consumers 13 100 kJ (3131 kcal);Pfor trend < 0·001). Fast-food consumers were more likely to exceed the RDA for energy, fat and saturated fat, and less likely to meet wholegrain and fruit recommendations. Both regular consumers (OR = 1·24; 95 % CI 1·03, 1·51) and occasional consumers (OR = 1·52; 95 % CI 1·32, 1·77) were more likely to have a waist:hip ratio indicating abdominal obesity. Occasional consumers were more likely to have a BMI ≥ 23·0 kg/m2(OR = 1·19; 95 % CI 1·04, 1·37), whereas regular consumers were less likely (OR = 0·76; 95 % CI 0·64, 0·91) to have an ‘at-risk’ BMI.

Conclusions

Fast-food consumption is most prevalent in young adults, high income and middle education level groups. Frequent fast-food consumption in Singapore is associated with unfavourable dietary and nutrient profiles and abdominal obesity.
Psychopathologische Aspekte von Sport
Authors: Zeeck Almut , Leonhart Rainer , Mosebach Nina , Schlegel Sabine , Linster Hans Wolfgang , Hartmann Armin
Published: August 2013

Die Exercise Dependence Scale (EDS-R) ist ein Instrument zum Screening von Sportsucht. Primäres Ziel der Studie war die Übersetzung des Fragebogens ins Deutsche und eine Replikation der Faktorstruktur. An einer Stichprobe von deutschsprachigen Studenten wurde mittels konfirmatorischer Faktoranalysen die Anpassungsgüte der amerikanischen Faktorlösung überprüft. Die sieben Faktoren ließen sich gut replizieren, jedoch bedürfen die Items des Faktors 5 („Reduction of Other Activities“) einer Überarbeitung. Im Vergleich mit anderen Instrumenten (Fragebogen zur Erfassung sportlicher Aktivität; Short Evaluation of Eating Disorders SEED, Exercise Motivations Inventory EMI-2) ergaben sich erste Hinweise auf Validität. Die replizierten Skalen der deutschen Version sind zur Erfassung von Symptomen einer Sportsucht insgesamt gut einsetzbar. Eine Diagnose sollte jedoch nur mittels zusätzlicher klinischer Beurteilung gestellt werden.
Obtaining Validity Evidence by Cognitive Interviewing to Interpret Psychometric Results
Authors: Padilla José-Luis , Benítez Isabel , Castillo Miguel
Published: August 2013

The latest edition of the Standards for Educational and Psychological Testing ( APA, 1999 ) promotes the analysis of respondents’ response processes in order to obtain evidence about the fit between the intended construct and the response process produced. The aim of this paper was twofold. First, we assess whether cognitive interviewing can be used to gather such validity evidence, and secondly, to analyze the usefulness of the evidence provided for interpreting the results from traditional psychometric analysis. The usefulness of the Cognitive Interviewing Reporting Framework ( Boeije & Willis, 2013 ) for reporting the cognitive interviewing findings was also evaluated. As an empirical example, we tested the (Spanish language) APGAR family function scale. A total of 21 pretest cognitive interviews were conducted, and psychometric analyzes were conducted of data from 28,371 respondents who were administered the APGAR scale. Results and utility of CIRF as a reporting framework are discussed.
Histological observations of a bilateral maxillary sinus floor elevation 6 and 12 months after grafting with osteogenic protein‐1 device
Authors: Groenveld H. H. J. , van den Bergh J. P. A. , Holzmann P. , ten Bruggenkate C. M. , Tuinzing D.B. , Burger E. H.
Published: August 2013

Abstract. Objective:The purpose of this case study was to analyze the tissue formed in a maxillary sinus, 6 and 12 months after grafting with recombinant human osteogenic protein‐I (OP‐I) linked to a collagen carrier of bovine origin.

Patient and methods: A 49‐year old woman referred for bilateral sinus floor elevation, was grafted with an OP‐l device. After 6 months, a biopsy was taken from one of the grafted areas. After 12 months, during implant placement, 5 biopsies were taken from the grafted area and the maxillary host bone. Biopsies were processed without decalcification for histological analyses.

Results: The biopsy taken after 6 months contained newly formed bone, fibrotic tissue and device remnants. After 12 months, however, bone was absent from all biopsies which were taken from the grafted area, while particles of the collagen carrier were still abundant. Inflammatory cells were observed between remnants of the collagen carrier in the grafted area.

Conclusion: This study indicates that an onset of new bone formation, which was observed after 6 months, did not persist. 12 months after grafting no bone was present in the biopsies from the grafted area, while the collagen carrier had remained. Lack of mechanical loading, as a result of postponing implant placement from 6 to 12 months, may have resulted in resorption of the emerging bone which was present 6 months after grafting.
Vulnerability of Polar Oceans to Anthropogenic Acidification: Comparison of Arctic and Antarctic Seasonal Cycles
Authors: Shadwick E. H. , Trull T. W. , Thomas H. , Gibson J. A. E.
Published: August 2013

Polar oceans are chemically sensitive to anthropogenic acidification due to their relatively low alkalinity and correspondingly weak carbonate buffering capacity. Here, we compare unique CO2 system observations covering complete annual cycles at an Arctic (Amundsen Gulf) and Antarctic site (Prydz Bay). The Arctic site experiences greater seasonal warming (10 vs 3°C) and freshening (3 vs 2), has lower alkalinity (2220 vs 2320 μmol/kg) and lower summer pH (8.15 vs 8.5), than the Antarctic site. Despite a larger uptake of inorganic carbon by summer photosynthesis, the Arctic carbon system exhibits smaller seasonal changes than the more alkaline Antarctic system. In addition, the excess surface nutrients in the Antarctic may allow mitigation of acidification, via CO2 removal by enhanced summer production driven by iron inputs from glacial and sea-ice melting. These differences suggest that the Arctic system is more vulnerable to anthropogenic change due to lower alkalinity, enhanced warming and nutrient limitation.
Mechanisms for the retention of inorganic N in acidic forest soils of southern China
Authors: Zhang Jin-bo , Cai Zu-cong , Zhu Tong-bin , Yang Wen-yan , Müller Christoph
Published: August 2013

The mechanisms underlying the retention of inorganic N in acidic forest soils in southern China are not well understood. Here, we simultaneously quantified the gross N transformation rates of various subtropical acidic forest soils located in southern China (southern soil) and those of temperate forest soils located in northern China (northern soil). We found that acidic southern soils had significantly higher gross rates of N mineralization and significantly higher turnover rates but a much greater capacity for retaining inorganic N than northern soils. The rates of autotrophic nitrification and NH3 volatilization in acidic southern soils were significantly lower due to low soil pH. Meanwhile, the relatively higher rates of NO3− immobilization into organic N in southern soils can counteract the effects of leaching, runoff and denitrification. Taken together, these processes are responsible for the N enrichment of the humid subtropical forest soils in southern China.
Optical and electrical effects of plasmonic nanoparticles in high-efficiency hybrid solar cells
Authors: Fu Wei-Fei , Chen Xiaoqiang , Yang Xi , Wang Ling , Shi Ye , Shi Minmin , Li Han-Ying , Jen Alex K.-Y. , Chen Jun-Wu , Cao Yong , Chen Hong-Zheng
Published: August 2013

Improved performance was obtained by doping a hole-transporting layer or active layer with Au nanoparticles in PCPDTBT–CdSe QD hybrid solar cells.
Robust spectrum sensing based on statistical tests
Authors: Arshad Kamran , Moessner Klaus
Published: August 2013

Spectrum sensing, in particular, detecting the presence of licensed or incumbent users in licensed spectrum, is one of the pivotal tasks in cognitive radio network. In this study, the authors tackle the spectrum sensing problem by using statistical test theory and derive novel spectrum sensing approaches. The authors apply the classical Kolmogorov–Smirnov (KS) test under the assumption that the noise probability distribution is known. However, as in practice, the exact noise distribution is unknown, a sensing method for Gaussian noise with unknown noise power is proposed in this article and referred to t‐sensing. The proposed sensing scheme is asymptotically robust and can be applied to non‐Gaussian noise distributions. A closed form equation determining the miss‐detection probability for the t‐sensing is derived. The authors compare with the performance of our sensing algorithms with the energy detector and Anderson–Darling (AD) sensing methods proposed in literature. Simulation results show that the proposed sensing methods outperform both ED‐ and AD‐based sensing, especially for the case when the received signal‐to‐noise ratio is low.
Distributed turbo coded cooperative networks under imperfect channel state information in Rayleigh fading channels
Authors: Chikha Haithem Ben , Dayoub Iyad , Berbineau Marion
Published: August 2013

In this study, under imperfect channel state information in Rayleigh fading channels, the authors analyse a previously proposed distributed turbo coded cooperative scheme based on parallel concatenated convolutional codes and soft‐decode‐and‐forward mode. For coherent binary phase shift keying over independent Rayleigh fading channels, the authors assume that the imperfect estimation errors are Gaussian distributed having a variance equal to a fraction of the variance of normalised Rayleigh distribution. Using the transfer function approach, the authors define an upper bound of the pairwise error probability to compute the average union upper bound for the bit error probability.
Blind iterative maximum likelihood‐based frequency and transition time estimation for frequency hopping systems
Authors: Fu Kuo‐Ching , Chen Yung‐Fang
Published: August 2013

Timing synchronisation and frequency estimation are two major estimation problems for frequency‐hopping spread spectrum systems. We present a blind scheme for estimating frequency and transition time in an iterative fashion: the iterative disassemble and assemble algorithm. The proposed scheme does not require initial random guesses as with common iterative algorithms. Improper initial guesses may suffer from the problem of convergence to the local maximum. The proposed approach can converge to the global maximum in order to achieve the solution. The proposed scheme offers a much lower computational complexity than that of the maximum‐likelihood greedy search algorithm. Moreover, it also outperforms existing schemes with comparable complexity. The simulation results demonstrate the efficacy of the proposed approach.
Efficient method for reducing the average control bits in a distributed cooperative sensing in cognitive radio system
Authors: Ghaznavi Mahsa , Jamshidi Azizollah
Published: August 2013

In cognitive radio (CR) networks, the incorrect detection of primary users causes inefficient spectrum utilisation and harmful interference to the primary users, so spectrum sensing is an important problem that must be well done. However, multipath fading and path loss effects always reduce the performance of spectrum sensing. Cooperative spectrum sensing improves the sensing performance of cognitive users. However, when the number of cognitive users cooperating with each other is very large, the reporting bits increase and therefore more bandwidth will be needed. In this study, the authors try to reduce the average number of control bits that is exchanged between CR users. The authors consider two different systems: single band detection system and wideband system. The analysis are done for perfect and imperfect control channels. By using a ring‐based distributed spectrum sensing model, they propose a method with little required bandwidth to inform the CRs from the final decision about the activity of the primary user. Analytical and numerical results show that this method reduces the average number of control bits and therefore the required control bandwidth. Moreover, the analytical results represent that the imperfect control channels do not affect the performance of the proposed single band system and has a little effect on the performance of our wideband scheme.
Design of a new interleaver using cross entropy method for turbo coding
Authors: Abderrahmane Lahcen Hadj
Published: August 2013

The main aim of this work is to find a way to improve a turbo code performance by designing a new interleaver structure based on the cross entropy (CE). The goal is to compare the performance of the CE method to a more popular interleaver such as the dithered golden interleaver. This study describes the performance of the turbo code – binary phase shift keying (BPSK) modem which was designed at the Instrumentation Division, Centre of Space Techniques. The simulation results are detailed in terms of the optimal solution observed along with the estimated bit‐error rate against Eb/N0. The authors compare the performance of turbo codes for different interleaver sizes and different number of iterations (resulting trade‐off curves) assuming two channel types (Gaussian and Rayleigh channels). For the simulated cases of the interleavers, good performance is obtained with the CE interleaver when transmitting data both in short block length (N = 400 bits), and long block length (N = 1024).
Joint beamforming design and base‐station assignment in a coordinated multicell system
Authors: Nguyen Duy H.N. , Le‐Ngoc Tho
Published: August 2013

This study is concerned with the downlink beamforming designs in a coordinated multicell system with dynamic base‐station (BS) assignment. At each cell, a multiple‐antenna BS employs linear beamforming to send multiple data streams to its assigned mobile‐stations (MSs). Exploiting multicell coordination, the multiple BSs jointly optimise the beamformers and the BS‐MS assignments to enhance the overall system performance. With per‐BS power constraints, considered are the coordinated beamforming problems under the following two design criteria: (i) minimising the transmit power margin at the BS with a set of target signal‐to‐interference‐plus‐noise ratios (SINR) at the MSs and (ii) jointly maximising the minimum SINR margin at the MSs. As the original problem formulations are shown to be non‐convex integer programs, which are combinatorially hard, the authors propose an efficient convex relaxation approach to solve the problems with low complexity. Simulations show that the convex relaxation‐based assignment schemes significantly outperform heuristic fixed assignment schemes.
Spatial modulation over K multiplicative complex fading wireless channels
Authors: Mzimkhulu Mthethwa Bhekisizwe , Xu Hongjun
Published: August 2013

The authors apply spatial modulation over multiplicative complex fading wireless channels, where the multiplicative complex fading is represented by the product of K statistically independent and identically distributed standard complex Gaussian random variables, where K ≥ 2. The analytical bit‐error rate (BER) approximation of symbol estimation is obtained in terms of a Meijer's G function. The conditional pairwise error probability (PEP) of transmit antenna index estimation is a function of a stochastic parameter with an unknown distribution function. The authors propose a lognormal distribution to approximate the distribution of this stochastic parameter. Based on the lognormal distribution, the average PEP and the analytical error probability upper bound of transmit antenna index estimation are derived. A goodness of fit test successfully validates the proposed lognormal distribution being the approximate distribution of the stochastic parameter. The derived analytical BER approximations for both symbol and transmit antenna index estimation are successfully validated via Monte Carlo simulations.
A low‐complexity relay selection scheme based on switch‐and‐examine diversity combining for AF relay systems
Authors: Salhab Anas M. , Zummo Salam A.
Published: August 2013

In this study, the authours present a low‐complexity relay selection scheme for channel‐state information (CSI)‐assisted dual‐hop amplify‐and‐forward cooperative systems. The scheme is mainly based on the switch‐and‐examine diversity combining (SEC) and SEC post‐selection (SECps) techniques in which a relay out of multiple relays is selected to forward the source signal to destination. The selection process is performed such that the selected relay signal‐to‐noise ratio (SNR) satisfies a predetermined switching threshold instead of best relay. Such a relay that satisfies this threshold will be chosen instead of the best relay. In this study, the authorsuse an upper bound on the end‐to‐end (e2e) SNR of the selection scheme and derive the probability density function and the cumulative distribution function of this SNR assuming the Rayleigh fading channels. These statistics are then used to derive accurate approximations for both the e2e outage probability and bit error probability, where the direct link in considered. The authours assume that maximal‐ratio combining is used at the destination to combine the signals through the relay and the direct link. To obtain more about system insights, the outage performance is studied at high SNR regime, where approximate expressions for the outage probability as well as the diversity order and coding gain are derived and analysed. The Monte‐Carlo simulations are provided to illustrate the validity of the analytical results and to show the tightness of the used SNR bound. Results illustrate the effectiveness of the proposed relaying schemes in reducing the required number of channel estimations and hence, reducing the system complexity compared with the opportunistic relaying. Furthermore, results show the gain achieved in the system performance; especially, at low‐to‐medium SNR values when the SECps selection scheme is used compared with the conventional SEC relaying. Finally, findings show that the system with the SEC and the SECps relaying schemes has the same diversity order of two and the same coding gain.
Pilot‐aided estimation and equalisation of a Radio‐over‐Fibre system in Wideband Code Division Multiple Access
Authors: Baghersalimi Gholamreza , O'Farrell Timothy
Published: August 2013

In this study, the impact of a Radio‐over‐Fibre (RoF) subsystem on the capacity performance of wideband code division multiple access is evaluated. This study investigates the use of pilot‐aided channel estimation to compensate for the optical subsystem non‐linearities for different channel conditions, estimation intervals and coding schemes. The results show that pilot‐aided channel estimation is an effective method for compensating the composite impairments of the optical subsystem and the radio frequency (RF) channel. It is found that there is always a suitable pilot power level which maximises the system capacity performance regardless of coding scheme and channel condition. Also, the peak capacity is only slightly affected by a decrease in the estimation interval.
Outage probability and bit‐error rate analysis of distributed antenna systems in multicell environment
Authors: Liu Yuxi , Liu Ju , Guo Weidong , Xu Hongji , Zhang Guowei , Yang Xiaohui
Published: August 2013

In this study, the authors investigate the outage probability and bit‐error rate (BER) of distributed antenna system in downlink multicell environment with blanket transmission. Different from the most existing works, the variance of interference plus noise is treated as a random variable other than constant, and it is influenced by the short term fading when propagation pathloss and transmit power are given. From the perspective of information theory, the closed‐form and approximate analytical expressions of downlink outage probability and average BER in the cellular system are derived for no shadowing and shadowing scenarios, respectively. Extensive simulation results validate the theoretical analysis and demonstrate that the system performances can be significantly improved for cell‐edge users. Moreover, the proposed analytical method can obtain more accurate system performances.
Survey on cooperative medium access control protocols
Authors: Ju Peijian , Song Wei , Zhou Dizhi
Published: August 2013

In the past decade, there has been ever‐increasing research attention to user cooperation in the wireless communication networks. The unique challenges of wireless networks such as channel fading and variation can be addressed well by taking advantage of relaying among cooperating mobile terminals. There are many studies on cooperative communications at the physical layer to exploit spatial diversity for improving channel capacity. In recent years, user cooperation from the perspective of the medium access control (MAC) layer becomes a promising new research area. In this study, the authors present a comprehensive survey on the mainstream cooperative MAC protocols in the literature. Focusing on the contention‐based solutions, the authors classify the well‐known proposals according to how they address two fundamental questions for user cooperation, that is, when to cooperation and whom to cooperate with. In addition to analysing the essential features of classic cooperative MAC protocols, the authors also discuss the major research challenges and project future research directions for MAC‐layer cooperation.
Comparison of reliability, delay and complexity for standalone cognitive radio spectrum sensing schemes
Authors: Liu Xing , Evans Barry G. , Moessner Klaus
Published: August 2013

The ability to reliably and autonomously identify unused frequency bands plays an extremely important role in cognitive radio networks. Relying on the spectrum sensing, ongoing licensed operation must not be compromised and the secondary spectrum usage efficiency should be maintained. Thus, it is critical to ensure that the confidence level of the estimated signal status satisfies the primary user's requirement, while keeping the delay and computational complexity to a minimum. This study provides a comprehensive comparison in terms of performance, reliability and complexity of standalone sensing schemes for various cognitive radio application areas. The authors first give some new results on reliability performance, and then evaluate the sensing time required to achieve the target performance. Finally, the authors compare the computational complexity of various sensing approaches by calculating the number of arithmetic operations required by each approach.
Soft‐decision decoding of convolutional codes with square‐law detectors
Authors: Nagaraj Santosh V. , Alimohammad Amirhossein
Published: August 2013

In this study, the authors investigate the performance of soft‐decision decoding of convolutional codes in receivers that employ square‐law detection. Traditionally, soft‐decision decoding has been considered only in coherent or differentially‐coherent receivers. Over the past few years, the emergence of ultra‐wideband (UWB) communication has brought energy detectors to prominence. In this study, the authors derive low‐complexity approximations for the log‐likelihood ratio (LLR) with a class of square‐law detectors in UWB radios. The authors then show that performance improvements, similar to those achievable in coherent detectors, can be obtained even with energy detectors when soft‐decisions are employed in a maximum‐likelihood decoding algorithm. The authors also investigate the complexity and accuracy of the proposed approximations when the LLR is computed using fixed point arithmetic. An expression for the bit error probability with soft‐decision decoding is derived. Several simulation results, including the error rate performance of hard‐ and soft‐decision decoding schemes with the exact and approximate LLR values, are presented.
Serrated cathode dissolution under high current density: Morphology and root cause
Authors: Yang T. L. , Ke J. H. , Shih W. L. , Lai Y. S. , Kao C. R.
Published: August 2013

Excessive cathode dissolution due to high current densities is investigated. Such excessive dissolution is one of the key electromigration-induced degradation processes in micro systems, and exhibits a distinctive serrated morphology. In this study, Cu cathode and Cu anode connected with Sn is stressed at a 4.5 × 104 A/cm2 current density for time as long as 1500 h. Careful sequential micro polishing is able to establish for the first time that the serrated cathode interface in fact is the expression of rod-like indentations in three-dimensional morphology. This unique morphology supports the proposition that fast Cu diffusion through Cu6Sn5 grain boundaries is the root cause for this excessive dissolution.
Thermal broadening of electron mobility distribution in AlGaN/AlN/GaN heterostructures
Authors: Asgari A. , Faraone L.
Published: August 2013

In this paper we present a detailed study of the effects of temperature on the two-dimensional electron mobility distribution, using a fully numerical calculation in unintentionally doped AlxGa1−xN/AlN/GaN heterostructures. The analysis of our results clearly indicates that the effect of partial sub-band occupancy is considerable, especially at higher operating temperatures when more than one sub-band is occupied. By correlating with published experimental data, our results are consistent with the observed broadening of the mobility distribution with increasing temperature, which is shown to be a direct consequence of the temperature dependence of polar optical phonons. Although other scattering mechanisms also affect broadening of the mobility distribution, the contribution from these other individual scattering mechanisms is found to be independent of temperature. In particular, a comparison of our calculated results with published experimental data is shown to be in excellent agreement across the temperature range from 100 K to 300 K. By fitting our model to experimental results at low temperatures (95 K–125 K), we are able to extract detailed information related to surface roughness scattering, which is dominant in this temperature range. In particular, the average height of interface roughness is found to be 18 A.
Wall current probe: A non-invasive in situ plasma diagnostic for space and time resolved current density distribution measurement
Authors: Baude R. , Gaboriau F. , Hagelaar G. J. M.
Published: August 2013

In the context of low temperature plasma research, we propose a wall current probe to determine the local charged particle fluxes flowing to the chamber walls. This non-intrusive planar probe consists of an array of electrode elements which can be individually biased and for which the current can be measured separately. We detail the probe properties and present the ability of the diagnostic to be used as a space and time resolved measurement of the ion and electron current density at the chamber walls. This diagnostic will be relevant to study the electron transport in magnetized low-pressure plasmas.
High efficient white organic light-emitting diodes with single emissive layer using phosphorescent red, green, and blue dopants
Authors: Kim You-Hyun , Wai Cheah Kok , Young Kim Woo
Published: August 2013

Phosphorescent white organic light-emitting diodes (PHWOLEDs) with single emissive layer were fabricated by co-doping phosphorescent blue, green, and red emitters with different concentrations. WOLEDs using Ir(piq)3 and Ir(ppy)3 as red and green dopants along with 8% of Firpic as blue dopant with host materials of 4CzPBP in the emissive layer were compared under various doping ratio between Ir(piq)3 and Ir(ppy)3. Triplet-triplet Dexter energy transfer in single emissive PHWOLEDs including three primary colors was saturated from higher triplet energy levels to lower triplet energy levels directly.
Electronic structure, phonon spectra and electron–phonon interaction in ScB2
Authors: Sichkar S. M. , Antonov V. N.
Published: August 2013

The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron–phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron–phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.
Spin glass behavior in A-site ordered YBaMn2O6 compound
Authors: Gao Qing-Qing , Li Jing-Bo , Li Guan-Nan , Rao Guang-Hui , Luo Jun , Liu Guang-Yao , Liang Jing-Kui
Published: August 2013

Magnetic properties of the A-site ordered YBaMn2O6 compound have been investigated by dc magnetic measurements. The divergence between zero-field-cooled and field-cooled susceptibilities at about 45 K suggests the presence of a spin-glass-like behavior. Thermal remnant magnetization, isothermal remnant magnetization, and memory effect measurements reveal the time relaxation of magnetization below 45 K, confirming the spin glass feature of the YBaMn2O6 sample. Detailed x-ray diffraction analysis demonstrates the existence of local antisite disorder on the ordered A sites, which might be the origin of the spin-glass behavior in the compound.
Geometric limits of coherent III-V core/shell nanowires
Authors: Salehzadeh O. , Kavanagh K. L. , Watkins S. P.
Published: August 2013

We demonstrate the application of a simple equilibrium model based on elasticity theory to estimate the geometric limits of dislocation-free core/shell nanowires (NWs). According to these calculations, in a coherent core/shell structure, tangential strain is the dominant component in the shell region and it decreases quickly away from the heterointerface, while axial strain is the dominant component in the core and is independent of the radial position. These strain distributions energetically favour the initial relief of axial strain in agreement with the experimental appearance of only edge dislocations with line directions perpendicular to the NW growth axis at the core/shell interfaces. Such dislocations were observed for wurtzite InAs/InP and zincblende GaAs/GaP core/shell NWs with dimensions above the coherency limits predicted by the model. Good agreement of the model was also found for experimental results previously reported for GaAs/InAs and GaAs/GaSb core/shell NWs.
Note on the hydrodynamic description of thin nematic films: Strong anchoring model
Authors: Lin Te-Sheng , Cummings Linda J. , Archer Andrew J. , Kondic Lou , Thiele Uwe
Published: August 2013

We discuss the long-wave hydrodynamic model for a thin film of nematic liquid crystal in the limit of strong anchoring at the free surface and at the substrate. We rigorously clarify how the elastic energy enters the evolution equation for the film thickness in order to provide a solid basis for further investigation: several conflicting models exist in the literature that predict qualitatively different behaviour. We consolidate the various approaches and show that the long-wave model derived through an asymptotic expansion of the full nemato-hydrodynamic equations with consistent boundary conditions agrees with the model one obtains by employing a thermodynamically motivated gradient dynamics formulation based on an underlying free energy functional. As a result, we find that in the case of strong anchoring the elastic distortion energy is always stabilising. To support the discussion in the main part of the paper, an appendix gives the full derivation of the evolution equation for the film thickness via asymptotic expansion.
Examining the phase transition behavior of amphiphilic lipids in solution using statistical temperature molecular dynamics and replica-exchange Wang-Landau methods
Authors: Gai Lili , Vogel Thomas , Maerzke Katie A. , Iacovella Christopher R. , Landau David P. , Cummings Peter T. , McCabe Clare
Published: August 2013

Two different techniques – replica-exchange Wang-Landau (REWL) and statistical temperature molecular dynamics (STMD) – were applied to systematically study the phase transition behavior of self-assembling lipids as a function of temperature using an off-lattice lipid model. Both methods allow the direct calculation of the density of states with improved efficiency compared to the original Wang-Landau method. A 3-segment model of amphiphilic lipids solvated in water has been studied with varied particle interaction energies (ɛ) and lipid concentrations. The phase behavior of the lipid molecules with respect to bilayer formation has been characterized through the calculation of the heat capacity as a function of temperature, in addition to various order parameters and general visual inspection. The simulations conducted by both methods can go to very low temperatures with the whole system exhibiting well-ordered structures. With optimized parameters, several bilayer phases are observed within the temperature range studied, including gel phase bilayers with frozen water, mixed water (i.e., frozen and liquid water), and liquid water, and a more fluid bilayer with liquid water. The results obtained from both methods, STMD and REWL, are consistently in excellent agreement with each other, thereby validating both the methods and the results.