bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Industrially Applied Heat‐Transfer Fluids as Liquid Organic Hydrogen Carrier Systems
Authors: Brückner Nicole , Obesser Katharina , Bösmann Andreas , Teichmann Daniel , Arlt Wolfgang , Dungs Jennifer , Wasserscheid Peter
Published: August 2013

Liquid organic hydrogen carrier (LOHC) systems offer a very attractive method for the decentralized storage of renewable excess energy. In this contribution, industrially well‐established heat‐transfer oils (typically sold under trade names, e.g., Marlotherm) are proposed as a new class of LOHC systems. It is demonstrated that the liquid mixture of isomeric dibenzyltoluenes (m.p. −39 to −34 °C, b.p. 390 °C) can be readily hydrogenated to the corresponding mixture of perhydrogenated analogues by binding 6.2 wt % of H2. The liquid H2‐rich form can be stored and transported similarly to diesel fuel. It readily undergoes catalytic dehydrogenation at temperatures above 260 °C, which proves its applicability as a reversible H2 carrier. The presented LOHC systems are further characterized by their excellent technical availability at comparably low prices, full registration of the H2‐lean forms, and excellent thermal stabilities.
Frailty and intellectual disability: A different operationalization?
Authors: Evenhuis Heleen , Schoufour Josje , Echteld Michael
Published: August 2013

Frailty is increasingly being recognized as a relevant health measure in older populations, associated with an increased risk of adverse health outcomes and care dependency. Because it is generally perceived that people with intellectual disabilities are “old” from age 50 onwards, frailty research in this group might lead to an understanding of factors, contributing to this perception. The development since the 1990s of conceptual and operational definitions of frailty has resulted in different approaches: biological (phenotype), multidimensional, and non‐specific deficit accumulation. All approaches consider disability a consequence rather than a cause of frailty. This may be different for long‐disabled populations, which would have consequences for validity of frailty measures. First research shows that the different approaches are applicable to study populations with intellectual disabilities as well. Frailty as defined by both the phenotypic and deficit accumulation approach appears to develop considerably earlier and is more severe in people with intellectual disabilities than in the general older population, supporting the notion of early aging. Before any clinical implications can be outlined, health outcomes (validity), causes, and prevention of frailty should be investigated. © 2013 Wiley Periodicals, Inc. Dev Disabil Res Rev 2013;18:17–21.
Fragile X syndrome: An aging perspective
Authors: Schneider Andrea , Ligsay Andrew , Hagerman Randi J.
Published: August 2013

Cognitive and behavioral correlates of molecular variations related to the FMR1 gene have been studied rather extensively, but research about the long‐term outcome in individuals with fragile X spectrum disorders remains sparse. In this review, we present an overview of aging research and recent findings in regard to cellular and clinical manifestations of aging in fragile X syndrome, and the FMR1 premutation. © 2013 Wiley Periodicals, Inc. Dev Disabil Res Rev 2013;18:68–74.
Drug laws and the 'derivative' problem
Authors: King Leslie A. , Ujváry István , Brandt Simon D.
Published: August 2013

The concept of a ‘derivative’ is used widely in chemistry, where its precise meaning depends on the circumstances. However, numerous examples of derivative also occur in domestic drugs legislation, some of which stem from the 1961 United Nations Single Convention on Narcotic Drugs. There is a commonly held view that only ‘first‐order’ derivatives should be considered: substances that can be created from a parent structure in a single chemical reaction. In other words, ‘derivatives of derivatives’ are excluded. However, some substances related to ecgonine (e.g. 2‐carbomethoxytropinone) are clearly convertible to cocaine, even though this may require more than one reaction step. It follows that 2‐carbomethoxytropinone is a controlled drug, a situation that most chemists would regard as perverse. A more extreme example of the complexity of ‘derivative’ is shown by the conversion of thebaine to buprenorphine. Even though this requires six or more stages, the US Drug Enforcement Administration successfully argued in a 1986 case that for the purposes of the Controlled Substances Act, the number of steps required was irrelevant; buprenorphine was a derivative of thebaine. Because the term derivative is rarely defined in statutes, the legal status of some substances, such as 2‐bromo‐LSD, is uncertain. Although a number of definitions of derivative can be found in the chemical literature, no single definition is adequate to describe all situations where it occurs in legislation. Unless qualified, it is suggested that the term derivative should be avoided in any future legislation. Copyright © 2013 John Wiley & Sons, Ltd.
Evaluating cloud tuning in a climate model with satellite observations
Authors: Suzuki Kentaroh , Golaz Jean‒Christophe , Stephens Graeme L.
Published: August 2013

This study examines the validity of a tunable cloud parameter, the threshold particle radius triggering the warm rain formation, in a climate model. Alternate values of the model's particular parameter within uncertainty have been shown to produce severely different historical temperature trends due to differing magnitude of aerosol indirect forcing. Three different threshold radii are evaluated against satellite observations in terms of the statistics depicting microphysical process signatures of the warm rain formation. The results show that the simulated temperature trend best matches to observed trend when the model adopts the threshold radius that worst reproduces satellite‒observed microphysical statistics and vice versa. This inconsistency between the “bottom‒up” process‒based constraint and the “top‒down” temperature trend constraint implies the presence of compensating errors in the model.
Phenotype profiling of primary testicular diffuse large B‐cell lymphomas
Authors: Menter Thomas , Ernst Martina , Drachneris Julius , Dirnhofer Stephan , Barghorn Andre , Went Philip , Tzankov Alexandar
Published: August 2013

Primary testicular diffuse large B‐cell lymphomas (tDLBCL) are rare neoplasms with few comprehensive studies conducted so far. We aimed to systematically characterize the phenotype of tDLBCL.

Forty‐five patients from three Swiss hospitals diagnosed with tDLBCL between 1972 and 2009 were reviewed and included in this study. A tissue microarray was assembled, and the protein expression profiles were assessed by immunohistochemistry and fluorescence in situ hybridization for the C‐MYC locus.

All tDLBCL expressed CD79a, followed by CD20 (98% of cases) and CD19 (93%). One case expressed the germ cell marker OCT4 and showed a rearrangement of C‐MYC. Eighty‐two per cent of cases showed active STAT signalling by expression of either pSTAT1 or pSTAT3 or both, but not pSTAT5. The p53 was overexpressed in 10% of cases, but p21 staining (∆p21/p53) did not suggest the presence of TP53 mutations. tDLBCL had a median MIB1 labelling index of 40%, and only 6% of cases appeared to have C‐MYC rearrangements. Most cases were of the non‐germinal centre type (77%), and showed as expected for this cell of origin B‐cell lymphoma 2 (BCL2) rearrangements only in 4% and amplifications in 15% of cases, whereas BCL6 was rearranged in 48% of cases. CXCR4 was expressed in 52% of cases, and high CXCR4 expression was of prognostic significance for progression‐free survival (p = 0.003). Because 84% of cases expressed nuclear p50, the canonical NF‐κB signalling pathway seems to be active.

Multimarker phenotyping is important for lineage determination of tDLBCL. Occasionally, tDLBCL can express germ cell markers like OCT4, and they have active STAT signalling mediated through pSTAT1 and pSTAT3 and active canonical NF‐κB signalling. tDLBCL are of non‐germinal centre/post‐germinal centre cell origin and not hyperproliferative. TP53 mutations are unlikely, and C‐MYC as well as BCL2 rearrangements are rare, whereas BCL6 is commonly rearranged. CXCR4 might prove to be the first protein‐based prognostic marker for tDLBCL, inciting studies in larger cohorts corroborating these findings. Copyright © 2013 John Wiley & Sons, Ltd.
Effective Molarity Redux: Proximity as a Guiding Force in Chemistry and Biology
Authors: Hobert Elissa M. , Doerner Amy E. , Walker Allison S. , Schepartz Alanna
Published: August 2013

The cell interior is a complex and demanding environment. An incredible variety of molecules jockey to identify the correct position – the specific interactions that promote biology, which are often hidden among countless unproductive options. Ensuring that the business of the cell is successful requires sophisticated mechanisms to impose temporal and spatial specificity – both on transient interactions and their eventual outcomes. Two strategies employed to regulate macromolecular interactions in a cellular context are colocalization and compartmentalization. Macromolecular interactions can be promoted and specified by localizing the partners within the same subcellular compartment, or by holding them in proximity through covalent or non‐covalent interactions with proteins, lipids, or DNA – themes that are familiar to any biologist. The net result of these strategies is an increase in effective molarity: the local concentration of a reactive molecule near its reaction partners. We will focus on this general mechanism, employed by nature and adapted in the lab, which allows delicate control in complex environments: the power of proximity to accelerate, guide, or otherwise influence the reactivity of signaling proteins and the information that they encode.
Assessment of incident spine and hip fractures in women and men using finite element analysis of CT scans
Authors: Kopperdahl David L , Aspelund Thor , Hoffmann Paul F , Sigurdsson Sigurdur , Siggeirsdottir Kristin , Harris Tamara B , Gudnason Vilmundur , Keaveny Tony M
Published: August 2013

Finite element analysis of computed tomography (CT) scans provides noninvasive estimates of bone strength at the spine and hip. To further validate such estimates clinically, we performed a 5-year case-control study of 1110 women and men over age 65 years from the AGES-Reykjavik cohort (case = incident spine or hip fracture; control = no incident spine or hip fracture). From the baseline CT scans, we measured femoral and vertebral strength, as well as bone mineral density (BMD) at the hip (areal BMD only) and lumbar spine (trabecular volumetric BMD only). We found that for incident radiographically confirmed spine fractures (n = 167), the age-adjusted odds ratio for vertebral strength was significant for women (2.8, 95% confidence interval [CI] 1.8 to 4.3) and men (2.2, 95% CI 1.5 to 3.2) and for men remained significant (p = 0.01) independent of vertebral trabecular volumetric BMD. For incident hip fractures (n = 171), the age-adjusted odds ratio for femoral strength was significant for women (4.2, 95% CI 2.6 to 6.9) and men (3.5, 95% CI 2.3 to 5.3) and remained significant after adjusting for femoral neck areal BMD in women and for total hip areal BMD in both sexes; fracture classification improved for women by combining femoral strength with femoral neck areal BMD (p = 0.002). For both sexes, the probabilities of spine and hip fractures were similarly high at the BMD-based interventional thresholds for osteoporosis and at corresponding preestablished thresholds for “fragile bone strength” (spine: women ≤ 4500 N, men ≤ 6500 N; hip: women ≤ 3000 N, men ≤ 3500 N). Because it is well established that individuals over age 65 years who have osteoporosis at the hip or spine by BMD criteria should be considered at high risk of fracture, these results indicate that individuals who have fragile bone strength at the hip or spine should also be considered at high risk of fracture. © 2014 American Society for Bone and Mineral Research.
Sonographic findings of pure ductal carcinoma in situ
Authors: Lee Mi Hee , Ko Eun Young , Han Boo‐Kyung , Shin Jung Hee , Ko Eun Sook , Hahn Soo Yeon
Published: August 2013

Purpose

To investigate the characteristic sonographic (US) findings of pure ductal carcinoma in situ (DCIS) in a large series.

Methods

We retrospectively reviewed the US findings of 126 cases of pure DCIS in 123 consecutive patients who underwent surgery for breast cancer in our hospital. We analyzed the US findings of the lesions according to mass or nonmass abnormality, shape, margin, orientation, echogenicity, echotexture, boundary echo, posterior acoustic features, presence of associated ductal dilatation, presence of intralesional cystic focus, and presence of microcalcifications on US. We compared the US characteristics of pure DCIS with and without mammographic microcalcifications.

Results

Seventy‐eight cases of pure DCIS had microcalcifications and 48 had no microcalcifications on mammography (MG). Overall, 109 cases (86.5%) of pure DCIS were demonstrated on US. DCIS with microcalcifications on MG showed positive US findings in 79.5% of cases. The most common US finding was heterogeneous hyper‐ or isoechoic parenchyma with intralesional microcalcifications and without posterior acoustic features. DCIS without microcalcifications on MG showed positive US findings in 97.9% of cases. The most common US findings were masses with round or oval shape, microlobulated margin, parallel orientation, heterogeneous mild hypoechogenicity, and without boundary echo or posterior acoustic features. Ductal dilatations and intralesional cystic foci were present in 17.5% (22/126) and 23.8% (30/126) of pure DCIS, respectively.

Conclusions

Overall, US could demonstrate 85.7% of pure DCIS cases, including 16 (12.7%) cases of clinically and mammographically occult pure DCIS. DCIS with and without microcalcifications on MG showed different US characteristics. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound, 41:465–471, 2013;
Geomorphic signatures of deltaic processes and vegetation: The Ganges‐Brahmaputra‐Jamuna case study
Authors: Passalacqua Paola , Lanzoni Stefano , Paola Chris , Rinaldo Andrea
Published: August 2013

Deltas are complex ecogeomorphic systems where features such as channels and interchannel islands are present over a wide range of spatial scales. A quantitative description of the morphology of deltas is fundamental to address how they react to changes in climate forcing and human pressure. In particular, it is interesting to ask how the distributary patterns we observe in coastal areas around the world result from processes and external forcing acting on deltas, and how such patterns might be related to deltaic function, vulnerability, and resilience. Using the example of the Ganges‐Brahmaputra‐Jamuna Delta, we show that the statistics of island size, shape factor, aspect ratio, and nearest‐edge distance show distinct spatial patterns. Comparison between regions identified by our statistical analysis and a physiographic zonation of the delta suggests that the planform extracted from satellite imagery carries the signature of processes responsible for delta formation and evolution and of vegetation. The tidal region is characterized by high channel density, small islands, and short nearest‐edge distance (shortest straight‐line distance to the nearest water). The results suggest that regions of the delta characterized by presence of vegetation and active transport of water and sediment are statistically distinct from less active regions. Further, we perform a weighted connectivity analysis of the channel patterns based on channel width. The analysis suggests that channels connecting the upper portion of the delta to the coast do not play a significant role in the transport of water and sediment.
Lee slope sediment processes leading to avalanche initiation on an aeolian dune
Authors: Sutton S. L. F. , McKenna Neuman C. , Nickling W.
Published: August 2013

In order to detail the governing conditions through which a slipface matures to the point of failure, dry sand avalanches were observed in the Dune Simulation Wind Tunnel on a 1:1 replica transverse dune with a crest height of approximately 1.2 m. Areal distributions of grainfall and reptation were measured using traps. Changes in the slipface elevation were observed using 3‐D laser scanning with a vertical accuracy of 0.096 mm for approximately every 1 mm2 of surface area. Grainfall decayed exponentially from the brink with a constant rate across all wind velocities. Reptation removed sediment from areas close to the brink and deposited it downslope, creating low amplitude, cross‐slope ripples on the slipface. A critical length scale separating grainscale and bulk sediment behavior is identified, and it defines the lower limit to the validity of angle of repose measurements. Avalanche initiation occurred in an area of steep surface slope below a sediment bulge, with distance from the brink independent of wind velocity. The time between avalanches was found to be constant for constant wind velocity.
Fast response liquid crystal mode
Authors: Lee Chung‐Yung , Tseng Man‐Chun , Kwok Hoi‐Sing
Published: August 2013

A novel fast nematic liquid crystal mode is proposed. It relies on the fast relaxation flow from bend state to the twisted state in the optically compensated bend mode. Such new liquid crystal mode is indeed an improved mode from the optically compensated bend mode as it does not require any holding voltage. The new liquid crystal mode has fast response time and high contrast. The proposed fast liquid crystal mode is a good candidate for applications, such as optical shutter, field sequential color display, and 3D display.
Emerging Synthetic Strategies for Core Cross‐Linked Star (CCS) Polymers and Applications as Interfacial Stabilizers: Bridging Linear Polymers and Nanoparticles
Authors: Chen Qijing , Cao Xueteng , Xu Yuanyuan , An Zesheng
Published: August 2013

Core cross‐linked star (CCS) polymers become increasingly important in polymer science and are evaluated in many value‐added applications. However, limitations exist to varied degrees for different synthetic methods. It is clear that improvement in synthetic efficiency is fundamental in driving this field moving even further. Here, the most recent advances are highlighted in synthetic strategies, including cross‐linking with cross‐linkers of low solubility, polymerization‐induced self‐assembly in aqueous‐based heterogeneous media, and cross‐linking via dynamic covalent bonds. The understanding of CCS polymers is also further refined to advocate their role as an intermediate between linear polymers and polymeric nanoparticles, and their use as interfacial stabilizers is rationalized within this context.

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The Design Carport – A self‐supporting folded steel sheet structure
Authors: Ernst Claudia , Brunier Knut
Published: August 2013

In the design and making of complex architectural systems, sheet metal is still predominantly used as a cladding material. The objective here is to integrate innovative digital and analogue methodologies to develop a design system for a self‐supporting lightweight structure entirely based on the use of sheet metal as a construction material.

A digital working methodology which is informed by fabrication techniques, material behavior and structural performance allows for a highly precise product and a coherent fabrication process.
Toward Paradigmatic Change in TESOL Methodologies: Building Plurilingual Pedagogies From the Ground Up
Authors: Lin Angel
Published: August 2013

Contemporary TESOL methodologies have been characterized by compartmentalization of languages in the classroom. However, recent years have seen the beginning signs of paradigmatic change in TESOL methodologies that indicate a move toward plurilingualism. In this article, the author draws on the case of Hong Kong to illustrate how, in the past four decades, deep‐rooted ideologies of linguistic purism combined with dominant TESOL knowledge claims have made it difficult to develop locally appropriate methodologies. She outlines the innovative work of some teachers who build up plurilingual pedagogies in content classrooms despite these difficulties, and on this basis proposes suggestions for future work.
Factor‐inhibiting hypoxia‐inducible factor expression in patients with high‐risk locally advanced renal cell carcinoma and its relationship with tumor progression
Authors: Deng Shi , Zhang Peng , Zeng Hao , Wang Wei , Jin Tao , Wang Jia , Dong Qiang
Published: August 2013

Hypoxia‐inducible factor (HIF) plays an important role in renal cell carcinoma (RCC) associated with angiogenesis. Factor‐inhibiting HIF (FIH), which is the upstream mediator protein of HIF, is receiving more attention today. In the present study, the role of FIH expression in high‐risk locally advanced renal cell carcinoma (LARCC) was explored. Eighty‐eight high‐risk LARCC cases were divided into two groups based on their prognosis. Using immunohistochemical staining, the correlations of FIH expression along with clinicopathological factors, progression‐free survival (PFS), and overall survival (OS) were analyzed. FIH was mainly located in the cytoplasm (34/88) and nucleus (31/88) of the renal tumor cell. Nuclear negative expression or cytoplasmic positive expression of FIH were associated with an increased risk of disease progression (p = 0.007 and p < 0.001, respectively) and worse OS (p = 0.020 and p = 0.008, respectively). Using the group with nuclear and cytoplasmic FIH negative expression as reference, further stratified analysis found that the exclusive nuclear FIH expression group had a better PFS and OS [hazard ratio (HR) = 0.153, p = 0.07 and HR = 0, p = 0.961, respectively], and the exclusive cytoplasmic FIH positive group experienced the worst PFS and OS (HR = 2.876, p = 0.005 and HR = 2.799, p = 0.034, respectively). In addition, nuclear negative expression of FIH was associated with a significant negative predictive value for the effect of interferon‐alpha (IFN‐α) on PFS (p = 0.045). The nuclear negative and cytoplasmic positive expressions of FIH were identified not only as risk factors for disease progression in high‐risk LARCC postoperative patients, but also to be associated with poor OS. Furthermore, the nuclear negative expression of FIH may be a promising biomarker for postoperative adjuvant therapy.
The role of cognitive event‐related potentials in executive dysfunction
Authors: Lai Chiou‐Lian , Lin Ruey‐Tay , Liou Li‐Min , Yang Yuan‐Han , Liu Ching‐Kuan
Published: August 2013

Frontal lobes are great and are a late‐developing region of the neocortex that play a critical role in human behavior and executive function. The aim of this study was to clarify the role of event‐related potentials (ERPs) in executive dysfunction and its relationship between generator mechanism and cognitive significance. We recruited 20 patients with frontal lobe lesion (FLL) and 27 age‐matched controls. All patients submitted to comprehensive Frontal Test Battery and auditory ERPs measurement. In comparison with controls, the patients with FLL had significantly decreased executive function and manifested the delay of P300 latency, which reflected a delay of mental processing speed in these patients. Our findings suggest that patients with FLL may have prolonged P300 latency, which has a good correlation with executive dysfunction, poor performance, and longer P300 latencies. P300 ERPs are considered to be a useful method to identify the alteration of frontal‐parietal connection.
Wavering Courts: From Impunity to Accountability in Uruguay
Authors: SKAAR ELIN
Published: August 2013

Many Latin American countries are moving towards increased accountability for past human rights violations, and there is a growing global consensus that international law does not allow some crimes simply to be exempted from prosecution. Uruguay has had a deeply split response to these developments. While the Supreme Court and the political elite increasingly pushed to end impunity, the public actually ratified the 1985 amnesty law protecting the military from prosecution in a 2009 plebiscite. The amnesty law was finally abolished by Parliament in 2011. This article traces the winding road from impunity to accountability in Uruguay in the context of substantial public support for impunity. It argues that, while the lack of judicial independence obstructed the quest for justice for many years, the combination of continued civil society demands for justice met by increasingly human-rights-friendly executives and liberal-minded judges (and lately also prosecutors) explains the recent advance in retributive justice.
Optimal power allocation for green cognitive radio: fractional programming approach
Authors: Naeem Muhammad , Illanko Kandasamy , Karmokar Ashok , Anpalagan Alagan , Jaseemuddin Muhammad
Published: August 2013

In this study, the problem of determining the power allocation that maximises the energy efficiency of cognitive radio network is investigated as a constrained fractional programming problem. The energy‐efficient fractional objective is defined in terms of bits per Joule per Hertz. The proposed constrained fractional programming problem is a non‐linear non‐convex optimisation problem. The authors first transform the energy‐efficient maximisation problem into a parametric optimisation problem and then propose an iterative power allocation algorithm that guarantees ε‐optimal solution. A proof of convergence is also given for the ε‐optimal algorithm. The proposed ε‐optimal algorithm provide a practical solution for power allocation in energy‐efficient cognitive radio networks. In simulation results, the effect of different system parameters (interference threshold level, number of primary users and number of secondary users) on the performance of the proposed algorithms are investigated.
How to understand linear minimum mean‐square‐error transceiver design for multiple‐input–multiple‐output systems from quadratic matrix programming
Authors: Xing Chengwen , Li Shuo , Fei Zesong , Kuang Jingming
Published: August 2013

In this study, a unified linear minimum mean‐square‐error (LMMSE) transceiver design framework is investigated, which is suitable for a wide range of wireless systems. The unified design is based on an elegant and powerful mathematical programming technology termed as quadratic matrix programming (QMP). Based on QMP it can be observed that for different wireless systems, there are certain common characteristics which can be exploited to design LMMSE transceivers, for example, the quadratic forms. It is also discovered that evolving from a point‐to‐point multiple‐input–multiple‐output (MIMO) system to various advanced wireless systems such as multi‐cell coordinated systems, multi‐user MIMO systems, MIMO cognitive radio systems, amplify‐and‐forward MIMO relaying systems and so on, the quadratic nature is always kept and the LMMSE transceiver designs can always be carried out via iteratively solving a number of QMP problems. A comprehensive framework on how to solve QMP problems is also given. The work presented in this study is likely to be the first shot for the transceiver design for the future ever‐changing wireless systems.
Design of efficient full‐rate linear dispersion space‐time block codes over correlated fading channels
Authors: Kuhestani Ali , Azmi Paeiz
Published: August 2013

In this study, the authors present a method to design efficient full‐rate linear dispersion space‐time block codes (LD‐STBCs) in correlated Rayleigh fading channels with simple detection at the receiver. The authors first derive a formula for the achievable capacity of an LD‐STBC coded multi‐input multiple‐output (MIMO) system as a function of correlation at the transmitter and the receiver. Moreover, the authors compute closed‐form bit‐error rate equations for multiple phase shift keying (M‐PSK) and multiple quadrature amplitude modulation (M‐QAM) schemes. Then, the authors present a method to construct LD‐STBCs over correlated Rayleigh fading MIMO channels. Finally, the authors design LD‐STBCs for two and four transmit antennas. The designed LD‐STBCs enjoy full‐rate, minimum power fluctuation, simple structure, simple processing at the receiver. Moreover, the designed LD‐STBCs for two transmit antennas provide better performance than Alamouti and LYC codes and the designed LD‐STBCs for four transmit antennas provide better performance than TV codes at practical signal‐to‐noise ratios. Simulation results show that when the proposed LD‐STBC for two transmit antennas is concatenated with an efficient outer channel encoder, it provides better performance than LYC code over correlated fading channels.
Performance analysis and power allocation for full‐rate and full‐diversity signal space cooperative communications
Authors: Lu Tao , Ge Jianhua , Yang Ye , Gao Yang
Published: August 2013

Signal space cooperative (SSC) system is bandwidth and energy efficient, which can achieve full‐rate and full‐diversity simultaneously. In this study, the authors first derive accurate bit error rate (BER) of the SSC system with maximum‐likelihood detection (MLD), low‐complexity linear detection (LD) and combined MLD and LD (MLD&LD). Specifically, closed‐form BER expressions for the three detection schemes are derived. Also, asymptotic approximation analysis is performed to show clearly the diversity and coding gains of the three detection schemes. Through the analysis, the authors find out that MLD is optimal in diversity but has a high complexity, whereas LD is of low complexity but only achieves diversity order one. Interestingly, MLD&LD has almost the same BER as the BER‐optimal MLD over the whole SNR range when equal power allocation (EPA) is adopted, whereas having lower complexity than MLD at low‐to‐medium SNR. Then, optimum power allocation for MLD&LD is developed, however, the largest power gain over EPA is proven to be only 0.37 dB. In view of the BER performance of MLD&LD and implementation simplicity of EPA, they conclude that MLD&LD with EPA is a wise choice for the SSC system. Finally, outage probability of MLD&LD with EPA is analysed to characterise the transmission reliability.
Multi‐objective optimisation technique for coupling matrix synthesis of lossy filters
Authors: Zhao Yuting , Wang Gang
Published: August 2013

Coupling matrix synthesis technique based on multi‐objective evolutionary algorithm (MOEA) is proposed for pseudoelliptic low‐pass filter prototypes with lossy resonators and arbitrary topology. MOEA‐based synthesis can deal with multi‐objective functions so that different filter characteristics of high‐performance lossy filter, such as return loss, out of band rejection and passband flatness, can be optimised simultaneously. In the proposed MOEA‐based lossy filter synthesis, a chromosome pair coding model is defined to treat real and imaginary parts of complex coupling matrix of a lossy filter, and additional constraints on Q‐factor to characterise lossy resonator in the filter are applied. For demonstration, non‐dominated sorting genetic algorithm II with extended arithmetic crossover and adaptive mutation operator are used to synthesise three symmetric/asymmetric lossy filters. The results indicate that the proposed MOEA‐based synthesis technique can provide perfect passband ripple as required in high‐performance microwave filters.
Frequency locked loop architecture for phase noise reduction in wideband low‐noise microwave oscillators
Authors: Ávila‐Ruiz Juan M. , Moreno‐Pozas Laureano , Durán‐Valdeiglesias Elena , Moscoso‐Mártir Alvaro , Molina‐Fernández Iñigo , de‐Oliva‐Rubio Jose
Published: August 2013

A frequency locked loop (FLL) for phase noise reduction of wideband voltage controlled oscillators is proposed. The key building block of the system is a low noise (−160 dBV/Hz) and high sensitivity (22 V/GHz) delay line frequency discriminator with 5–8 GHz coverage, which makes use of a high performance multilayer hybrid. The authors derive closed‐form, universal design equations for the maximum noise reduction and stability of the FLL circuitry. Application of the proposed technique to a state‐of‐the‐art voltage controlled oscillator operating in the 5–8 GHz band yields a phase noise reduction of 8–10 dB at 100 kHz and 5 dB at 1 MHz off the carrier, which shows the results are in good agreement with the simulated results; so phase noise better than −107 dBc/Hz at 100 kHz and better than −123.5 dBc/Hz at 1 MHz is obtained.
Propagation channel measurements and analysis at 2.4 GHz in subway tunnels
Authors: He Ruisi , Zhong Zhangdui , Ai Bo , Guan Ke , Chen Binghao , AIonso Jose I. , Briso Cesar
Published: August 2013

The reliability of communication systems in a subway tunnel requires an absolute understanding of the propagation channel in this environment. From an insightful look at the subway channel and especially when compared with the other underground propagation environments such as mines, roads and railway tunnels, an important feature of the subway tunnel is the existence of stations in the tunnel. These stations cause extra reflection in the channel and also increase the delay spread observed. Although this effect has been largely neglected in available propagation channel literature, this is an important concept that ought to be explored. In this work, the authors present channel measurements conducted close to a station in a subway tunnel at 2.4 GHz, using a self‐developed frequency domain channel sounder. To aid the authors analysis, three typical propagation regions are defined: line‐of‐sight (LOS), non‐LOS and far‐LOS, and also use a larger observation delay window to investigate the long delay clusters caused by the existence of stations in subway tunnel. From the analysis of the power delay profile (PDP), root‐mean‐square delay spread and scattering function in the three propagation regions, the authors have been able to infer a long delay cluster of about 2 µs, which the authors attributed to multipath propagation of signal along the tunnel and reflections in the station. The Saleh–Valenzuela model is used to characterise the long clustering phenomenon observed in the PDP. The results show that the time spreading in subway tunnel is more significant because of the station compared with other underground tunnels, which leads to substantial signal distortion.
Efficiency droop in InGaN/GaN blue light-emitting diodes: Physical mechanisms and remedies
Authors: Verzellesi Giovanni , Saguatti Davide , Meneghini Matteo , Bertazzi Francesco , Goano Michele , Meneghesso Gaudenzio , Zanoni Enrico
Published: August 2013

Physical mechanisms causing the efficiency droop in InGaN/GaN blue light-emitting diodes and remedies proposed for droop mitigation are classified and reviewed. Droop mechanisms taken into consideration are Auger recombination, reduced active volume effects, carrier delocalization, and carrier leakage. The latter can in turn be promoted by polarization charges, inefficient hole injection, asymmetry between electron and hole densities and transport properties, lateral current crowding, quantum-well overfly by ballistic electrons, defect-related tunneling, and saturation of radiative recombination. Reviewed droop remedies include increasing the thickness or number of the quantum wells, improving the lateral current uniformity, engineering the quantum barriers (including multi-layer and graded quantum barriers), using insertion or injection layers, engineering the electron-blocking layer (EBL) (including InAlN, graded, polarization-doped, and superlattice EBL), exploiting reversed polarization (by either inverted epitaxy or N-polar growth), and growing along semi- or non-polar orientations. Numerical device simulations of a reference device are used through the paper as a proof of concept for selected mechanisms and remedies.
Control of the Ge nanocrystal synthesis by co-implantation of Si+
Authors: Barba D. , Demarche J. , Martin F. , Terwagne G. , Ross G. G.
Published: August 2013

The synthesis of Ge nanocrystals (Ge-nc) prepared by 74Ge+ implantation into fused silica followed by co-implantation of Si+ has been investigated for annealing temperatures varying between 850 and 1150 °C. By limiting the thermal diffusion of Ge, co-implanting Si reduces the Ge desorption and affects the growth of Ge-nc, through a Ge trapping mechanism involving the formation of Ge-Si chemical bonds. This is supported by Raman analysis, providing information regarding the material composition for a large variety of fabrication parameters, as well as high resolution scanning electron microscopy imaging, indicating that the average dimension of the synthesized Ge-nc decreases for increasing doses of co-implanted Si. From the spectral analysis of Raman measurements, a systematic evolution of the Ge-Ge, Ge-Si, and Si-Si bond concentrations is characterized as a function of the co-implantation fluences. Two different regimes are clearly identified for each annealing temperature. The first is associated with a linear increase of the residual Ge content with respect to the co-implanted Si, having a slope of ∼1, independent of the annealing temperature. Here, the nucleation of pure Ge-nc and Ge-nc containing Si impurities occurs at similar rates, for co-implanted Si fluences generally lower than the dose of implanted Ge. The second regime occurs for greater co-implantation fluence thresholds that depend on the annealing temperature. It is related to the saturation of the Ge trapping efficiency. In this regime, the formation of Si-Ge bonds dominates, sufficiently reducing the diffusion of Ge to prevent the formation of pure Ge-nc. In addition to limiting the unwanted and critical Ge desorption effects, Si co-implantation is a promising technique for precisely controlling the Ge-nc density, diameter, and uniformity at nanoscale dimensions, parameters which cannot be solely set from the local Ge concentration and/or the annealing parameters due to the high thermal diffusivity of Ge.
Photoelectron spectroscopic and density functional theoretical studies of the 2′-deoxycytidine homodimer radical anion
Authors: Storoniak Piotr , Rak Janusz , Ko Yeon Jae , Wang Haopeng , Bowen Kit H.
Published: August 2013

The intact (parent) 2′-deoxycytidine homodimer anion, (dC)2•−, was generated in the gas phase (in vacuo) using an infrared desorption/photoemission source and its photoelectron spectrum was recorded using a pulsed, magnetic bottle photoelectron spectrometer. The photoelectron spectrum (PES) revealed a broad peak with the maximum at an electron binding energy between 1.6 and 1.9 eV and with a threshold at ∼1.2 eV. The relative energies and vertical detachment energies of possible anion radicals were calculated at the B3LYP/6-31++G** level of theory. The most stable anion radicals are the complexes involving combinations of the sugar···base and base···base interactions. The calculated adiabatic electron affinities and vertical detachment energies of the most stable (dC)2•− anions agree with the experimental values. In contrast with previous experimental-computational studies on the anionic complexes involving nucleobases with various proton-donors, the electron-induced proton transferred structures of (dC)2•− are not responsible for the shape of PES.
Magnetic shape memory effect at 1.7 K
Authors: Heczko Oleg , Kopecký Vít , Sozinov Alexei , Straka Ladislav
Published: August 2013

Magnetic shape memory effect or magnetically induced structure reorientation (MIR) occurred down to 1.7 K in 10 M martensite with composition of Ni50.0Mn27.5Ga22.5 exhibiting no intermartensite transformation. The reorientation of the martensite microstructure was mediated by the motion of single Type II twin boundary. In contrast with weak thermal dependence of Type II boundary, MIR with Type I boundary in the same alloy showed strong thermal dependence resembling normal thermal activation process and the effect disappeared below 220 K. Thus the type of the boundary is decisive for MIR at low temperatures.
Modeling electrical conductivity of nanocomposites by considering carbon nanotube deformation at nanotube junctions
Authors: Gong S. , Zhu Z. H. , Haddad E. I.
Published: August 2013

This paper investigates the effect of carbon nanotube (CNT) deformation on the electrical conductivity of CNT polymer composites at crossed nanotube junctions using a revised 3-dimensional CNT percolating network model. Two aspects of the work are considered. The first is concerned with the effect of CNT deformation on its intrinsic and contact resistances at CNT-CNT junctions. An analytical model based on electron ballistic tunneling theory and Landauer-Büttiker formula is proposed to describe the variation of CNT-CNT contact resistance at the CNT-CNT junction in terms of local deformation of CNT walls and CNT-CNT distance. In addition, a model exclusively based on experimental data to describe the change of CNT intrinsic resistance in terms of its cross-section deformation is adopted. The second is concerned with the relationship among the CNT-CNT distance, the angle between two adjacent CNTs, and the dimensions of local deformation of CNT walls and its impact on the corresponding intrinsic and contact resistance of CNTs near and at a CNT-CNT junction. Finally, Monte Carlo simulations are conducted to evaluate these effects on the electrical conductivity of nanocomposites for different CNT weight fractions. Our results reveal that the local deformation of CNT walls plays a significant role in the evaluation of electrical conductivity of CNT polymer composites. The intrinsic resistance in the deformed part of CNTs near a CNT-CNT junction increases much faster than the decrease of CNT-CNT contact resistance at the same junction when two CNTs are getting closer, resulting in a net increase of resistance at the junction. Numerical results show that the current model agrees with existing experimental data better than existing models without considering the effect of CNT deformation, which tends to overestimate the electrical conductivity of CNT polymer composites containing homogeneously dispersed percolating CNT network.
Energy levels of exciton in a gapped graphene sheet
Authors: Fallah Farhang , Esmaeilzadeh Mahdi
Published: August 2013

A theory is presented for exciton formation in a graphene sheet using the center-of-mass approximation. The energy levels and wavefunctions of exciton are calculated analytically which show that the exciton can form if the band gap of graphene is not zero. We show that the energy gap of graphene plays the role of the mass which if not zero, leads to formation of the excitons. It is shown that the main quantum number of the exciton ground state changes with the graphene dielectric constant. Also, all of the states are found to be four-fold degenerate. The binding energy of exciton can reach as high as 1/4 of the energy gap of graphene which is notable among the conventional quasi-2D systems. This result can play an important rule in the photonics of graphene.
Phase locking route behind complex periodic windows in a forced oscillator
Authors: Jan Hengtai , Tsai Kuo-Ting , Kuo Li-wei
Published: August 2013

Chaotic systems have complex reactions against an external driving force; even in cases with low-dimension oscillators, the routes to synchronization are diverse. We proposed a stroboscope-based method for analyzing driven chaotic systems in their phase space. According to two statistic quantities generated from time series, we could realize the system state and the driving behavior simultaneously. We demonstrated our method in a driven bi-stable system, which showed complex period windows under a proper driving force. With increasing periodic driving force, a route from interior periodic oscillation to phase synchronization through the chaos state could be found. Periodic windows could also be identified and the circumstances under which they occurred distinguished. Statistical results were supported by conditional Lyapunov exponent analysis to show the power in analyzing the unknown time series.
Electrowetting at a liquid metal-semiconductor junction
Authors: Arscott Steve , Gaudet Matthieu
Published: August 2013

We report electrowetting at a liquid metal-semiconductor (Schottky) junction using of a mercury droplet resting on silicon. This is demonstrated using n-type and p-type single-crystal silicon wafers of different doping levels. The voltage-dependent wetting contact angle variation of the mercury droplet is observed to depend on both the underlying semiconductor doping density and type. The electrowetting behavior can be explained by the voltage-dependent modulation of the capacitance of a Schottky junction; current-voltage and capacitance-voltage measurements indicate this to be the case. A modified Young-Lippmann electrowetting equation—formulated using a well-established metal-semiconductor junction model—agrees well with the observations.
Resistive switching in rectifying interfaces of metal-semiconductor-metal structures
Authors: Zazpe R. , Stoliar P. , Golmar F. , Llopis R. , Casanova F. , Hueso L. E.
Published: August 2013

We study the electrical characteristics of metal-semiconductor-metal HfO2−x-based devices where both metal-semiconductor interfaces present bipolar resistive switching. The device exhibits an unusual current-voltage hysteresis loop that arises from the non-trivial interplay of the switching interfaces. We propose an experimental method to disentangle the individual characteristics of each interface based on hysteresis switching loops. A mathematical framework based on simple assumptions allows us to rationalize the whole behavior of the device and reproduce the experimental current-voltage curves of devices with different metallic contacts. We show that each interface complementarily switches between a nonlinear metal-semiconductor interface and an ohmic contact.
Identification of nnp and npp Auger recombination as significant contributor to the efficiency droop in (GaIn)N quantum wells by visualization of hot carriers in photoluminescence
Authors: Binder M. , Nirschl A. , Zeisel R. , Hager T. , Lugauer H.-J. , Sabathil M. , Bougeard D. , Wagner J. , Galler B.
Published: August 2013

We report the direct observation of hot carriers generated by Auger recombination via photoluminescence spectroscopy on tailored (AlGaIn)N multiple quantum well (QW) structures containing alternating green and ultra-violet (UV) emitting (GaIn)N QWs. Optically pumping solely the green QWs using a blue emitting high power laser diode, carrier densities similar to electrical light-emitting diode (LED) operation were achieved, circumventing possible leakage and injection effects. This way, luminescence from the UV QWs could be observed for excitation where the emission from the green QWs showed significant droop, giving direct evidence for Auger generated hot electrons and holes being injected into the UV QWs. An examination of the quantitative relation between the intensity of the UV luminescence and the amount of charge carriers lost due to drooping of the QWs supports the conclusion that Auger processes contribute significantly to the droop phenomenon in (AlGaIn)N based light-emitting diodes.
High performance field emission properties of graphite nanoplatelet field emitters
Authors: Song Yenan , Hoon Shin Dong , Song Yoon-Ho , Saito Yahachi , Jin Lee Cheol
Published: August 2013

Graphite nanoplatelet (GNP) that consists of several tens of layers of graphene sheets is a promising candidate for electron field emission. The GNP emitter shows good field emission properties with a high emission current and a robust long-term stability because of the sharp edges, the high aspect ratio, and the stacked graphene sheets. Most of the electrons are emitted from the sharp edges of GNPs. The GNP emitters fabricated by the screen printing method reveal the turn-on electric field of 1.77 V/μm, the threshold electric field of 4.47 V/μm, the maximum emission current density of 39 mA/cm2, and the good emission stability for 20 h with little degradation rate of the emission current. The GNP field emitters can be a good candidate for several field emission applications such as flat lamps, field emission displays, and x-ray sources.