bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of interactions of polypyrimidine tract-binding protein with artificial internal ribosome entry segments
Authors: Spriggs K.A. , Mitchell S.A. , Willis A.E.
Published: August 2015

Most eukaryotic translation initiation is thought to be dependent on the 5′-cap structure of the mRNA. It is becoming apparent, however, that the mRNAs of many genes contain IRESs (internal ribosome entry segments) within the 5′-UTR (5′-untranslated region) that allow ribosomes to initiate translation independently of the 5′-cap. IRESs can enable the expression of these genes under conditions (such as viral infection, cellular stress and apoptosis) when cap-dependent translation initiation is compromised, and also provide a target for regulation of gene expression. Recent results from our laboratory and others suggest that 10% of mRNAs (∼4000 genes) use this mechanism to initiate translation. One of the central goals of those working in the field of translation is to identify the sequence motif(s) and proteins that are required for internal ribosome entry. We have identified recently a unique PTB (polypyrimidine tract-binding protein) motif (CCU)n that is present in a large subset of cellular IRESs, and the results suggest that PTB itself is involved either directly or indirectly in ribosome recruitment. Here, we describe further investigations of PTB with artificial sequences that harbour this motif.
Characterization of AWAP IV, the C-terminal domain of the avian protein AWAK
Authors: Townes C.L. , Milona P. , Hall J.
Published: August 2015

AWAP IV constitutes the C-terminal domain of the larger 81 kDa protein AWAK [Avian WAP (whey acidic protein) domain- and Kunitz domain-containing], which is predicted, through conserved domain database searching, to contain at least four WAP domains and one Kunitz domain. RT (reverse transcription)–PCR analyses revealed mRNA transcripts encoding AWAP IV in the small intestinal and kidney tissues of 5-day-old Salmonella-infected chicks. Time-kill antimicrobial assays using rAWAP IV (recombinant AWAP IV) cell lysate indicated antimicrobial activity against Gram-positive and Gram-negative bacteria including Salmonella, Streptococcus and Staphylococcus spp. In addition, permeabilization of the outer membrane of Salmonella, as shown by the NPN (N-phenyl-1-naphthylamine) fluorescent probe assay, supported the ability of rAWAP IV to disrupt prokaryotic membranes. WAP domains can function as inhibitors of serine protease activity, and the microbial serine proteases subtilisin and proteinase K were inhibited by rAWAP IV cell lysate. However, at comparable concentrations, no significant inhibition of the mammalian serine protease elastase was observed. The combined broad-spectrum antibacterial and anti-protease activities of AWAP IV suggest a novel role in the avian innate defence mechanisms operating against microbial infection.
Hot and crispy: CRISPR–Cas systems in the hyperthermophile Sulfolobus solfataricus
Authors: Zhang Jing , White Malcolm F.
Published: August 2015

The CRISPR (clustered regularly interspaced short palindromic repeats) and Cas (CRISPR-associated) genes are widely spread in bacteria and archaea, representing an intracellular defence system against invading viruses and plasmids. In the system, fragments from foreign DNA are captured and integrated into the host genome at the CRISPR locus. The locus is transcribed and the resulting RNAs are processed by Cas6 into small crRNAs (CRISPR RNAs) that guide a variety of effector complexes to degrade the invading genetic elements. Many bacteria and archaea have one major type of effector complex. However, Sulfolobus solfataricus strain P2 has six CRISPR loci with two families of repeats, four cas6 genes and three different types of effector complex. These features make S. solfataricus an important model for studying CRISPR–Cas systems. In the present article, we review our current understanding of crRNA biogenesis and its effector complexes, subtype I-A and subtype III-B, in S. solfataricus. We also discuss the differences in terms of mechanisms between the subtype III-B systems in S. solfataricus and Pyrococcus furiosus.
A snapshot of Snf2 enzymes in fission yeast
Authors: Prasad Punit , Ekwall Karl
Published: August 2015

Eukaryotic chromatin is remodelled by the evolutionarily conserved Snf2 family of enzymes in an ATP-dependent manner. Several Snf2 enzymes are part of CRCs (chromatin remodelling complexes). In the present review we focus our attention on the functions of Snf2 enzymes and CRCs in fission yeast. We discuss their molecular mechanisms and roles and in regulating gene expression, DNA recombination, euchromatin and heterochromatin structure.
The search for better epilepsy treatments: from slime mould to coconuts
Authors: Walker Matthew C. , Williams Robin S.B.
Published: August 2015

Drug-resistant epilepsy has remained a problem since the inception of antiepileptic drug development, despite the large variety of antiepileptic drugs available today. Moreover, the mechanism-of-action of these drugs is often unknown. This is due to the widespread screening of compounds through animal models. We have taken a different approach to antiepileptic drug discovery and have identified a biochemical pathway in Dictyostelium discoideum (a ‘slime mould’) that may relate to the mechanism-of-action of valproate, one of the most commonly used and effective antiepileptic drugs. Through screening in this pathway, we have been able to identify a whole host of fatty acids and fatty acid derivatives with potential antiepileptic activity; this was then confirmed in in vitro and in vivo mammalian seizure models. Some of these compounds are more potent than valproate and potentially lack many of the major side effects of valproate (including birth defects and liver toxicity). In addition, one of the compounds that we have identified is a major constituent of the ketogenic diet, strongly arguing that it may be the fatty acids and not the ketogenesis that are mediating the effect of this diet.
The links between chromatin spatial organization and biological function
Authors: Rodriguez Alejandro , Bjerling Pernilla
Published: August 2015

During the last few years, there has been a rapid increase in our knowledge of how chromatin is organized inside the nucleus. Techniques such as FISH (fluorescence in situ hybridization) have proved that chromosomes organize themselves in so-called CTs (chromosome territories). In addition, newly developed 3C (chromatin conformation capture) techniques have revealed that certain chromosomal regions tend to interact with adjacent regions on either the same chromosome or adjacent chromosomes, and also that regions in close proximity are replicated simultaneously. Furthermore, transcriptionally repressed or active areas occupy different nuclear compartments. Another new technique, named DamID (DNA adenine methyltransferase identification), has strengthened the notion that transcriptionally repressed genes are often found in close association with the nuclear membrane, whereas transcriptionally active regions are found in the more central regions of the nucleus. However, in response to various stimuli, transcriptionally repressed regions are known to relocalize from the nuclear lamina to the interior of the nucleus, leading to a concomitant up-regulation of otherwise silenced genes. Taken together, these insights are of great interest for the relationship between chromosomal spatial organization and genome function. In the present article, we review recent advances in this field with a focus on mammalian cells and the eukaryotic model organism Schizosaccharomyces pombe.
Regulation of chromosome dynamics by Hsk1/Cdc7 kinase
Authors: Matsumoto Seiji , Masai Hisao
Published: August 2015

Hsk1 (homologue of Cdc7 kinase 1) of the fission yeast is a member of the conserved Cdc7 (cell division cycle 7) kinase family, and promotes initiation of chromosome replication by phosphorylating Mcm (minichromosome maintenance) subunits, essential components for the replicative helicase. Recent studies, however, indicate more diverse roles for Hsk1/Cdc7 in regulation of various chromosome dynamics, including initiation of meiotic recombination, meiotic chromosome segregation, DNA repair, replication checkpoints, centromeric heterochromatin formation and so forth. Hsk1/Cdc7, with its unique target specificity, can now be regarded as an important modulator of various chromosome transactions.
The spindle assembly checkpoint: progress and persistent puzzles
Authors: Hauf Silke
Published: August 2015

The spindle assembly checkpoint is a conserved mitotic signalling pathway that ensures the equal segregation of chromosomes to daughter cells. Despite intensive work in many model organisms, key features of this safety mechanism remain unexplained. In the present review, I briefly summarize advances made in the last few years, and then focus on unexplored corners of this signalling pathway.
Insight into a neuron's preferential susceptibility to oxidative stress
Authors: Bell Karen F.S.
Published: August 2015

Neurons are more vulnerable to oxidative stress than astrocytes, the reasons for which have yet to be fully elucidated. Understanding the cellular and molecular mechanisms which contribute to this enhanced vulnerability is key to efforts aimed at ameliorating neuronal health and resilience to oxidative stress, particularly in the context of neurodegenerative disease, which is characterized by progressive dysfunction and loss of neurons specifically, and in which oxidative stress is considered a central aetiological contributor. Biological factors which may influence neuronal susceptibility to oxidative stress, in normal and neurodegenerative contexts, are reviewed in the present article, with a focus on properties intrinsic to the neuronal cell type and on properties related to neuronal reliance on surrounding astrocytes.
Enzymatic protein depalmitoylation by acyl protein thioesterases
Authors: Lin David T.S. , Conibear Elizabeth
Published: August 2015

Protein palmitoylation is a dynamic post-translational modification, where the 16-carbon fatty acid, palmitate, is added to cysteines of proteins to modulate protein sorting, targeting and signalling. Palmitate removal from proteins is mediated by acyl protein thioesterases (APTs). Although initially identified as lysophospholipases, increasing evidence suggests APT1 and APT2 are the major APTs that mediate the depalmitoylation of diverse cellular substrates. Here, we describe the conserved functions of APT1 and APT2 across organisms and discuss the possibility that these enzymes are members of a larger family of depalmitoylation enzymes.
Postsynaptic nanodomains generated by local palmitoylation cycles
Authors: Fukata Masaki , Sekiya Atsushi , Murakami Tatsuro , Yokoi Norihiko , Fukata Yuko
Published: August 2015

Precise regulation of protein assembly at specialized membrane domains is essential for diverse cellular functions including synaptic transmission. However, it is incompletely understood how protein clustering at the plasma membrane is initiated, maintained and controlled. Protein palmitoylation, a common post-translational modification, regulates protein targeting to the plasma membrane. Such modified proteins are enriched in these specialized membrane domains. In this review, we focus on palmitoylation of PSD-95, which is a major postsynaptic scaffolding protein and makes discrete postsynaptic nanodomains in a palmitoylation-dependent manner and discuss a determinant role of local palmitoylation cycles in creating highly localized hotspots at the membrane where specific proteins concentrate to organize functional domains.
Wnt acylation and its functional implication in Wnt signalling regulation
Authors: Janda Claudia Y. , Garcia K. Christopher
Published: August 2015

Wnt proteins are conserved signalling molecules that have an essential role in regulating diverse processes during embryogenesis and adult tissue homoeostasis. Wnts are post-translationally modified by palmitoylation, which is essential for Wnt secretion and function. Intriguingly, the crystal structure of XWnt8 in complex with the extracellular domain of the Frizzled 8 cysteine-rich domain (Fzd8-CRD) revealed that Wnts use the fatty acid as a ‘hotspot’ residue to engage its receptor, which is a unique mode of receptor-ligand recognition. In addition, there are several lines of evidence suggesting that Wnts engage several signalling modulators and alternative receptors by means of fatty acids as a critical contact residue. In the present article, we review our current understanding of Wnt acylation and its functional role in Wnt signalling regulation.
Palmitoylation and palmitoyl-transferases in Plasmodium parasites
Authors: Hodson Nicola , Invergo Brandon , Rayner Julian C. , Choudhary Jyoti S.
Published: August 2015

Protein post-translational modifications (PTM) are commonly used to regulate biological processes. Protein S-acylation is an enzymatically regulated reversible modification that has been shown to modulate protein localization, activity and membrane binding. Proteome-scale discovery on Plasmodium falciparum schizonts has revealed a complement of more than 400 palmitoylated proteins, including those essential for host invasion and drug resistance. The wide regulatory affect on this species is endorsed by the presence of 12 proteins containing the conserved DHHC–CRD (DHHC motif within a cysteine-rich domain) that is associated with palmitoyl-transferase activity. Genetic interrogation of these enzymes in Apicomplexa has revealed essentiality and distinct localization at cellular compartments; these features are species specific and are not observed in yeast. It is clear that palmitoylation has an elaborate role in Plasmodium biology and opens intriguing questions on the functional consequence of this group of acylation modifications and how the protein S-acyl transferases (PATs) orchestrate molecular events.
Modelling biomacromolecular assemblies with continuum mechanics
Authors: Hanson Benjamin , Richardson Robin , Oliver Robin , Read Daniel J. , Harlen Oliver , Harris Sarah
Published: August 2015

We have developed a continuum mechanical description of proteins using a finite element algorithm which has been generalized to include thermal fluctuations and which is therefore known as fluctuating finite element analysis (FFEA). Whereas conventional molecular dynamics (MD) simulations provide a trajectory in which each individual atomic position fluctuates, a FFEA trajectory shows how the overall shape of the protein changes due to thermal agitation. We describe the theoretical background to FFEA, its relationship to more established biomolecular modelling methods and provide examples of its application to the mesoscale biomolecular dynamics of the molecular motor dynein.
Novel insights into the regulation of cyclooxygenase-2 expression by platelet-cancer cell cross-talk
Authors: Dovizio Melania , Alberti Sara , Sacco Angela , Guillem-Llobat Paloma , Schiavone Simone , Maier Thorsten J. , Steinhilber Dieter , Patrignani Paola
Published: August 2015

Platelets are activated by the interaction with cancer cells and release enhanced levels of lipid mediators [such as thromboxane (TX)A2 and prostaglandin (PG)E2, generated from arachidonic acid (AA) by the activity of cyclooxygenase (COX)-1], granule content, including ADP and growth factors, chemokines, proteases and Wnt proteins. Moreover, activated platelets shed different vesicles, such as microparticles (MPs) and exosomes (rich in genetic material such as mRNAs and miRNAs). These platelet-derived products induce several phenotypic changes in cancer cells which confer high metastatic capacity. A central event involves an aberrant expression of COX-2 which influences cell-cycle progression and contribute to the acquisition of a cell migratory phenotype through the induction of epithelial mesenchymal transition genes and down-regulation of E-cadherin expression. The identification of novel molecular determinants involved in the cross-talk between platelets and cancer cells has led to identify novel targets for anti-cancer drug development.
PINK1 activation–turning on a promiscuous kinase
Authors: Aerts Liesbeth , De Strooper Bart , Morais Vanessa A.
Published: August 2015

PINK1 [phosphatase and tensin homologue (PTEN)-induced putative kinase 1] is a serine/threonine kinase targeted to mitochondria and implicated in early-onset recessive Parkinson's disease (PD). Through the phosphorylation of its downstream targets, PINK1 regulates multiple mitochondrial processes, including ATP production, stress-response and mitochondrial dynamics and quality control. The orchestration of such a wide array of functions by an individual kinase requires a fine-tuned and versatile regulation of its activity. PINK1 proteolytic processing, trafficking and localization, as well as different post-translational modifications, affect its activity and function. Unravelling the regulatory mechanisms of PINK1 is essential for a full comprehension of its kinase function in health and disease.
Dissecting molecular cross-talk between Nrf2 and NF-κB response pathways
Authors: Wardyn Joanna D. , Ponsford Amy H. , Sanderson Christopher M.
Published: August 2015

In most tissues, cells are exposed to frequent changes in levels of oxidative stress and inflammation. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and nuclear factor-κB (NF-κB) are the two key transcription factors that regulate cellular responses to oxidative stress and inflammation respectively. Pharmacological and genetic studies suggest that there is functional cross-talk between these two important pathways. The absence of Nrf2 can exacerbate NF-κB activity leading to increased cytokine production, whereas NF-κB can modulate Nrf2 transcription and activity, having both positive and negative effects on the target gene expression. This review focuses on the potentially complex molecular mechanisms that link the Nrf2 and NF-κB pathways and the importance of designing more effective therapeutic strategies to prevent or treat a broad range of neurological disorders.
Structure of the mammalian TSPO/PBR protein
Authors: Jaremko Mariusz , Jaremko Łukasz , Jaipuria Garima , Becker Stefan , Zweckstetter Markus
Published: August 2015

The 3D structure of the 18-kDa transmembrane (TM) protein TSPO (translocator protein)/PBR (peripheral benzodiazepine receptor), which contains a binding site for benzodiazepines, is important to better understand its function and regulation by endogenous and synthetic ligands. We have recently determined the structure of mammalian TSPO/PBR in complex with the diagnostic ligand PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide; Jaremko et al. (2014) Science 343, 1363–1366], providing for the first time atomic-level insight into the conformation of this protein, which is up-regulated in various pathological conditions including Alzheimer's disease and Parkinson's disease. Here, we review the studies which have probed the structural properties of mammalian TSPO/PBR as well as the homologues bacterial tryptophan-rich sensory proteins (TspOs) over the years and provide detailed insight into the 3D structure of mouse TSPO (mTSPO)/PBR in complex with PK11195.
Guwiyang Wurra–‘Fire Mouse’: a global gene knockout model for TSPO/PBR drug development, loss-of-function and mechanisms of compensation studies
Authors: Middleton Ryan J. , Liu Guo-Jun , Banati Richard B.
Published: August 2015

The highly conserved 18-kDa translocator protein (TSPO) or peripheral benzodiazepine receptor (PBR), is being investigated as a diagnostic and therapeutic target for disease conditions ranging from inflammation to neurodegeneration and behavioural illnesses. Many functions have been attributed to TSPO/PBR including a role in the mitochondrial permeability transition pore (MPTP), steroidogenesis and energy metabolism. In this review, we detail the recent developments in determining the physiological role of TSPO/PBR, specifically based on data obtained from the recently generated Tspo knockout mouse models. In addition to defining the role of TSPO/PBR, we also describe the value of Tspo knockout mice in determining the selectivity, specificity and presence of any off-target effects of TSPO/PBR ligands.
Translocator protein: pharmacology and steroidogenesis
Authors: Midzak Andrew , Zirkin Barry , Papadopoulos Vassilios
Published: August 2015

The translocator protein (TSPO; 18k Da) is an evolutionarily conserved outer mitochondrial membrane (OMM) protein highly expressed in steroid-synthesizing cells and found to possess a number of physiological and drug-binding partners. Extensive pharmacological, biochemical and cell biological research over the years has led to a model of TSPO involvement in mitochondrial cholesterol transport and promotion of steroid synthesis, a model guiding the design of drugs useful in stimulating neurosteroid synthesis and alleviating psychopathological symptoms. The involvement of TSPO in these processes has been called into question; however, with the publication of TSPO-deletion mouse models which saw no changes in steroid production. Here, we review work characterizing TSPO in steroidogenesis and offer perspective to research into TSPO pharmacology and its involvement in steroid biosynthesis.
The intestinal immunoendocrine axis: novel cross-talk between enteroendocrine cells and the immune system during infection and inflammatory disease
Authors: Worthington John J
Published: August 2015

The intestinal epithelium represents one of our most important interfaces with the external environment. It must remain tightly balanced to allow nutrient absorption, but maintain barrier function and immune homoeostasis, a failure of which results in chronic infection or debilitating inflammatory bowel disease (IBD). The intestinal epithelium mainly consists of absorptive enterocytes and secretory goblet and Paneth cells and has recently come to light as being an essential modulator of immunity as opposed to a simple passive barrier. Each epithelial sub-type can produce specific immune modulating factors, driving innate immunity to pathogens as well as preventing autoimmunity. The enteroendocrine cells comprise just 1% of this epithelium, but collectively form the bodies’ largest endocrine system. The mechanisms of enteroendocrine cell peptide secretion during feeding, metabolism and nutrient absorption are well studied; but their potential interactions with the enriched numbers of surrounding immune cells remain largely unexplored. This review focuses on alterations in enteroendocrine cell number and peptide secretion during inflammation and disease, highlighting the few in depth studies which have attempted to dissect the immune driven mechanisms that drive these phenomena. Moreover, the emerging potential of enteroendocrine cells acting as innate sensors of intestinal perturbation and secreting peptides to directly orchestrate immune cell function will be proposed. In summary, the data generated from these studies have begun to unravel a complex cross-talk between immune and enteroendocrine cells, highlighting the emerging immunoendocrine axis as a potential target for therapeutic strategies for infections and inflammatory disorders of the intestine.
Mean square error analysis and linear minimum mean square error application for preamble‐based channel estimation in orthogonal frequency division multiplexing/offset quadrature amplitude modulation systems
Authors: Savaux Vincent , Bader Faouzi
Published: August 2015

In this study, the performance of different preamble‐based channel estimation techniques is analysed for orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) modulation systems. Three pilot allocation methods, the pair of pilot, the interference cancellation method, and the interference approximation method are considered. A theoretical expression of the estimation mean square error (MSE) is performed for each of them, which considers the selectivity of the channel and the interferences from all the neighbouring time–frequency positions. Moreover, an application of the linear minimum MSE estimator in OFDM/OQAM is investigated and an analysis of its MSE performance is provided as well. It is shown that, due to the intrinsic interference, the MSE of the channel estimation inevitably reaches an error floor whatever the applied method is. Numerical results show that the theoretical MSE assessments match those obtained by simulation. In addition to the MSE, the bit error rate performance for the different channel estimators is depicted.
Near optimal power allocation in two‐way relay systems with physical layer network coding
Authors: Chen Chen , Bai Lin , Yang Yehua , Jin Ye , Choi Jinho
Published: August 2015

In this study, the authors examine the power allocation (PA) in a two‐way relay system, where the relay adopts physical layer network coding based on decode‐and‐forward protocol. In the PA, the optimisation objective is to minimise the end‐to‐end symbol error probability (SEP) under a total power constraint. Since the optimal power allocation (OPA) scheme requires numerical methods (for exhaustive search) to find the solution, which might be infeasible for practical systems, the authors propose a near optimal power allocation (NOPA) scheme that has a closed‐form solution by studying the properties of the OPA scheme. The asymptotic SEP expression of the proposed NOPA scheme is also derived. Simulation results show that the performance of proposed NOPA scheme is quite close to that of the OPA scheme. Furthermore, it is shown that the NOPA scheme can provide asymptotic SNR gains of 1.76 dB and 2.22 dB over two well‐known schemes.
Stochastic multiple‐input multiple‐output channel model based on singular value decomposition
Authors: Liu Yang , Yu Yu , Lu Wen‐Jun , Zhu Hong‐bo
Published: August 2015

A novel stochastic multiple‐input multiple‐output (MIMO) channel model based on the singular value decomposition of the channel matrix is proposed in this study. Under the framework of the proposed model, each of the right singular vectors can be modelled as the product of a stochastic scalar and a non‐random vector, as is each of the left singular vectors. The non‐random vectors, defined as the eigenmodes of the transmitter and receiver, respectively, can be easily extracted from the measurements, so are the singular values of the channel matrix. The implications of the proposed model's parameters that provide further insight into the MIMO channel are interpreted and a way of exploiting the parameters is given. To validate the proposed model, MIMO channel measurement is carried out under different indoor environments and the channel capacity is analysed. It is shown that the proposed model provides a better fit to the measurement results than the other popular stochastic channel models. The proposed stochastic MIMO channel model can be used for the MIMO communication system design and evaluation.
Vibration control of a Timoshenko beam system with input backlash
Authors: He Wei , Liu Chang
Published: August 2015

In this study, a novel boundary control algorithm is designed for a class of Timoshenko beams with unknown external disturbance and uncertain input backlash non‐linearity. The Timoshenko beam is described by partial differential equations as governing equations and ordinary differential equations as boundary conditions. The representation of input backlash is modified as a desired control input associated with input non‐linear error, which will be transformed into the external disturbance. The unknown ‘disturbance‐like’ item is defined based on input error and disturbance, and the boundary of this unknown ‘disturbance‐like’ item will be estimated by a disturbance observer. The unknown backlash can be handled and the ultimately uniform stability of the closed‐loop system is ensured. Numerical simulations are provided to verify the performance of the author's proposed control.
Robust inverse compensation and control of a class of non‐linear systems with unknown asymmetric backlash non‐linearity
Authors: Gu Guo‐Ying , Su Chun‐Yi , Zhu Li‐Min
Published: August 2015

A robust control approach with the inverse backlash compensation is presented for a class of non‐linear systems preceded by unknown asymmetric backlash non‐linearity. Firstly, the analytical expressions of the inverse compensation error for an asymmetric backlash are obtained by introducing new indicator functions, which make it possible to design a corresponding controller for the asymmetric input backlash. With the developed compensation error expression, conventional robust control approaches can be utilised to deal with such a non‐smooth non‐linear system. As an illustration, a robust adaptive control strategy is applied to demonstrate the approach. The developed control laws ensure the robust inverse compensation and achieve tracking within a desired accuracy. Finally, simulations performed on an unstable and uncertain non‐linear system illustrate and clarify the effectiveness of the developed approach.
Robust stochastic stability and delayed‐state‐feedback stabilisation of uncertain Markovian jump linear systems with random time delays
Authors: Qiu Li , Shi Yang , Xu Bugong , Yao Fengqi
Published: August 2015

The problem of robust stochastic stability and delayed‐state‐feedback stabilisation of uncertain Markovian jump linear systems with random Markov delays is investigated. Based on the Lyapunov stability theory and robust analysis techniques, some robust stochastic stability criteria are derived in terms of linear matrix inequalities. Robust delayed‐state‐feedback controllers that stochastically stabilise the uncertain Markovian jump linear systems is also proposed. The state variable on the controller is assumed to be dependent on the Markov delay that has uncertain transition probabilities. Finally, numerical examples are provided to illustrate the feasibility and effectiveness of the proposed methods.
Finite horizon optimal tracking control of partially unknown linear continuous‐time systems using policy iteration
Authors: Li Chao , Liu Derong , Li Hongliang
Published: August 2015

In this study, a neural‐network‐based online learning algorithm is established to solve the finite horizon linear quadratic tracking (FHLQT) problem for partially unknown continuous‐time systems. An augmented problem is constructed with an augmented state which consists of the system state and the reference trajectory. The authors obtain a solution for the augmented problem which is equivalent to the standard solution of the FHLQT problem. To solve the augmented problem with partially unknown system dynamics, they develop a time‐varying Riccati equation. A critic neural network is used to approximate the value function and an online learning algorithm is established using the policy iteration technique to solve the time‐varying Riccati equation. An integral policy iteration method and an online tuning law are used when the algorithm is implemented without the knowledge of the system drift dynamics and the command generator dynamics. A simulation example is given to show the effectiveness of the established algorithm.
Enhanced damping‐based anti‐swing control method for underactuated overhead cranes
Authors: Wu Xianqing , He Xiongxiong
Published: August 2015

In this study, a novel enhanced anti‐swing control method is proposed for underactuated overhead crane systems, which shows superior anti‐swing control performance than most existing control methods. In particular, to increase the anti‐swing control performance of overhead crane systems, an improved damping anti‐swing signal is investigated based on a swing‐related storage function. Subsequently, based on the anti‐swing signal, a constructive Lyapunov function candidate is introduced and a new non‐linear anti‐swing control method is proposed straightforwardly, and the equilibrium point of the overall closed‐loop system is proven to be asymptotically stable by Lyapunov techniques and LaSalle's invariance theorem. Some experimental results are provided to demonstrate the feasibility and effectiveness of the proposed control method. In addition, to illustrate the superior control performance of the proposed method, a comparison study between the designed control method and the existing control methods is provided as well.
High‐performance hybrid photovoltaic ‐battery system based on quasi‐Z‐source inverter: application in microgrids
Authors: Khajesalehi Jasem , Sheshyekani Keyhan , Hamzeh Mohsen , Afjei Ebrahim
Published: August 2015

This study presents a high‐performance photovoltaic (PV)‐battery hybrid power conversion system (HPCS) which is integrated to a microgrid using a quasi‐Z‐source inverter (qZSI). The battery system is directly connected to the intermediate dc link of the qZSI without any extra converter which reduces the size and the cost of the power electronic interface. A controller equipped with a harmonic compensator is designed to control the battery current in the grid‐connected mode and to regulate the microgrid voltage in the islanded mode in the presence of unbalanced and non‐linear loads. Furthermore, the proposed controller adjusts the shoot‐through duty cycle of the qZSI to regulate the PV voltage to its reference value provided through the maximum power point tracking algorithm. Moreover, the proposed controller provides the microgrid with the capability to transfer between the two operation modes. A new strategy is adopted to keep the HPCS operational in case of severe reduction in the available power of the PV modules and its consequent voltage drop. The performance of the proposed control system is evaluated for the control of a typical microgrid simulated in MATLAB/SIMULINK environment.
Optimum design of low‐voltage distributed photovoltaic systems oriented to enhanced fault ride through capability
Authors: Perpinias Ioannis I. , Papanikolaou Nick P. , Tatakis Emmanuel C.
Published: August 2015

The prescribed perspective of high accession of distributed generation photovoltaic (DG‐PV) units on low‐voltage distribution networks has brought up many issues regarding their performance in case of network transient phenomena. In this study, the design principles that DG‐PV units must incorporate in order to meet the requirements of low‐voltage ride through capability (LVRTC) are investigated through detailed theoretical analysis and calculations. The analysis shows that a realistic over‐sizing of interfaced inverters of DG‐PV as well as an appropriate selection of the equivalent interconnecting reactance XDG, in conjunction with high penetration levels, can lead to satisfaction of LVRTC demands without violating the protection limits of the network. Moreover, the scenario of uniform dispersion along the distribution lines is proved rather favourable concerning the demand of LVRTC for voltage selectivity. Finally, considering the derived outcomes, a methodology of optimum design about LVRTC is proposed within the framework of reasonable constraints, which can be applied to any low‐voltage distribution network.
Load frequency control of a hydro‐thermal system under deregulated environment using biogeography‐based optimised three‐degree‐of‐freedom integral‐derivative controller
Authors: Rahman Asadur , Saikia Lalit Chandra , Sinha Nidul
Published: August 2015

This study presents the load frequency control of an interconnected two‐area power system under deregulated environment with area1 as a thermal system having two generating companies and area2 as hydro‐thermal system. Appropriate generation rate constraint, and governor dead band are provided in the areas. Three‐degree‐of‐freedom integral‐derivative (3DOF‐ID) controllers are used as secondary controllers in the areas whose performance is compared with that of two‐degree‐of‐freedom integral‐derivative (2DOF‐ID) and single‐degree‐of‐freedom controllers such as integral (I), integral‐derivative (ID). Biogeography‐based optimisation (BBO) technique is used for simultaneous optimisation of controller gains and electric governor parameters. Analysis of the dynamic responses reveal the superiority of 3DOF‐ID controller over I, ID, and 2DOF‐ID controllers, in terms of settling time, peak deviation and magnitude of oscillation. Sensitivity analysis proved that, BBO optimised parameters obtained at nominal conditions are robust. 3DOF‐ID controller parameters obtained at nominal distribution companies participation matrix (DPM) are healthy enough and not necessary to optimise for change in DPMs. Variation in frequency bias coefficient (B) concludes that the best selection for B is equal to area frequency response characteristics. Similarly, selection of governor speed regulation parameter (R) infers higher value for thermal‐system, while hydro‐system should be kept comparatively low.
Wireless coexistence and interference test method for low‐power wireless sensor networks
Authors: Serra Ramiro , Nabi Majid
Published: August 2015

Wireless sensor networks (WSNs) are being increasingly introduced for critical applications such as safety, security and health. One the main characteristic requirements of such networks are that they should function with relative low power. Therefore the wireless links are more vulnerable. Successfully testing wireless coexistence and potential vulnerabilities of such networks against interference is of crucial importance. Reverberation chambers represent a successful environment for various tests regarding performance evaluation of wireless communication systems. In this study, the authors propose a test methodology specifically developed for assessing WSNs performance under different channel and interference conditions.
Combining surface effects and non‐local two variable refined plate theories on the shear/biaxial buckling and vibration of silver nanoplates
Authors: Karimi Morteza , Haddad Hojjat Allah , Shahidi Ali Reza
Published: August 2015

In this reported work, surface effects and non‐local two variable refined plate theories are combined on the shear/biaxial buckling and vibration of rectangular nanoplates. A silver sheet is selected as the case study to investigate the numerical results. Surface effects are considered by Gurtin–Murdoch's theory. The differential quadrature method is used to solve the governing equations. Differential quadrature solutions are verified by Navier's method. The influences of the non‐local parameter on the surface effects of shear/biaxial buckling and vibration are investigated for various boundary conditions. Results show that by increasing the non‐local parameter, the effects of surface on the buckling and vibration increase. This result is in contrast with the works of other researchers in the field. Moreover, the non‐local effects on the shear buckling and vibration are more important than that of biaxial, whereas the surface effects on the biaxial buckling and vibration are more notable than that of shear.
Continuity of the maximum-entropy inference: Convex geometry and numerical ranges approach
Authors: Rodman Leiba , Spitkovsky Ilya M. , Szkoła Arleta , Weis Stephan
Published: August 2015

We study the continuity of an abstract generalization of the maximum-entropy inference—a maximizer. It is defined as a right-inverse of a linear map restricted to a convex body which uniquely maximizes on each fiber of the linear map a continuous function on the convex body. Using convex geometry we prove, amongst others, the existence of discontinuities of the maximizer at limits of extremal points not being extremal points themselves and apply the result to quantum correlations. Further, we use numerical range methods in the case of quantum inference which refers to two observables. One result is a complete characterization of points of discontinuity for 3 × 3 matrices.
Weak solutions and blow-up for wave equations of p-Laplacian type with supercritical sources
Authors: Pei Pei , Rammaha Mohammad A. , Toundykov Daniel
Published: August 2015

This paper investigates a quasilinear wave equation with Kelvin-Voigt damping, utt − Δpu − Δut = f(u), in a bounded domain Ω ⊂ ℝ3 and subject to Dirichlét boundary conditions. The operator Δp, 2 < p < 3, denotes the classical p-Laplacian. The nonlinear term f(u) is a source feedback that is allowed to have a supercritical exponent, in the sense that the associated Nemytskii operator is not locally Lipschitz from W01,p(Ω) into L2(Ω). Under suitable assumptions on the parameters, we prove existence of local weak solutions, which can be extended globally provided the damping term dominates the source in an appropriate sense. Moreover, a blow-up result is proved for solutions with negative initial total energy.
Benchmark calculations on the nuclear quadrupole-coupling parameters for open-shell molecules using non-relativistic and scalar-relativistic coupled-cluster methods
Authors: Cheng Lan
Published: August 2015

Quantum-chemical computations of nuclear quadrupole-coupling parameters for 24 open-shell states of small molecules based on non-relativistic and spin-free exact two-component (SFX2C) relativistic equation-of-motion coupled-cluster (EOM-CC) as well as spin-orbital-based restricted open-shell Hartree-Fock coupled-cluster (ROHF-CC) methods are reported. Relativistic effects, the performance of the EOM-CC and ROHF-CC methods for treating electron correlation, as well as basis-set convergence have been carefully analyzed. Consideration of relativistic effects is necessary for accurate calculations on systems containing third-row (K-Kr) and heavier elements, as expected, and the SFX2C approach is shown to be a useful cost-effective option here. Further, it is demonstrated that the EOM-CC methods constitute flexible and accurate alternatives to the ROHF-CC methods in the calculations of nuclear quadrupole-coupling parameters for open-shell states.
On new scaling of dielectric response
Authors: Gałązka M. , Juszyńska-Gałązka E. , Osiecka N. , Massalska-Arodź M. , Bąk A.
Published: August 2015

We present a new generalized scaling relationship accounting for relaxation processes of both the real and the imaginary parts of the complex dielectric permittivity data in a wide temperature range of dielectric media. It has been successfully used for experimental data related to various dynamics in liquid crystalline phases of: 4-bromobenzylidene-4′-pentyloxyanilin, 4-bromobenzylidene-4′-hexyloxyaniline, 4′-butyl-4-(2-methylbutoxy) azoxybenzene, and 4-ethyl-4′-octylazoxybenzene. Moreover, the scaling was checked for the theoretical data of Dissado-Hill cluster model. A comparison with earlier scaling, proposed by Nagel and Dendzik, is given.
Photoluminescence study of p-type vs. n-type Ag-doped ZnO films
Authors: Myers M. A. , Khranovskyy V. , Jian J. , Lee J. H. , Wang Han , Wang Haiyan
Published: August 2015

Silver doped ZnO films have been grown on sapphire (0001) substrates by pulsed laser deposition. Hall measurements indicate that p-type conductivity is realized for the films deposited at 500 °C and 750 °C. Transmission electron microscopy images show more obvious and higher density of stacking faults (SFs) present in the p-type ZnO films as compared to the n-type films. Top view and cross sectional photoluminescence of the n- and p-type samples revealed free excitonic emission from both films. A peak at 3.314 eV, attributed to SF emission, has been observed only for the n-type sample, while a weak neutral acceptor peak observed at 3.359 eV in the p-type film. The SF emission in the n-type sample suggests localization of acceptor impurities nearby the SFs, while lack of SF emission for the p-type sample indicates the activation of the Ag acceptors in ZnO.
Mixing effects in the crystallization of supercooled quantum binary liquids
Authors: Kühnel M. , Fernández J. M. , Tramonto F. , Tejeda G. , Moreno E. , Kalinin A. , Nava M. , Galli D. E. , Montero S. , Grisenti R. E.
Published: August 2015

By means of Raman spectroscopy of liquid microjets, we have investigated the crystallization process of supercooled quantum liquid mixtures composed of parahydrogen (pH2) or orthodeuterium (oD2) diluted with small amounts of neon. We show that the introduction of the Ne impurities affects the crystallization kinetics in terms of a significant reduction of the measured pH2 and oD2 crystal growth rates, similarly to what found in our previous work on supercooled pH2-oD2 liquid mixtures [Kühnel et al., Phys. Rev. B 89, 180201(R) (2014)]. Our experimental results, in combination with path-integral simulations of the supercooled liquid mixtures, suggest in particular a correlation between the measured growth rates and the ratio of the effective particle sizes originating from quantum delocalization effects. We further show that the crystalline structure of the mixtures is also affected to a large extent by the presence of the Ne impurities, which likely initiate the freezing process through the formation of Ne-rich crystallites.
Measuring temperature and field profiles in heat assisted magnetic recording
Authors: Hohlfeld J. , Zheng X. , Benakli M.
Published: August 2015

We introduce a theoretical and experimental framework that enables quantitative measurements of the temperature and magnetic field profiles governing the thermo-magnetic write process in heat assisted magnetic recording. Since our approach allows the identification of the correct temperature dependence of the magneto-crystalline anisotropy field in the vicinity of the Curie point as well, it provides an unprecedented experimental foundation to assess our understanding of heat assisted magnetic recording.
High-throughput sorting of drops in microfluidic chips using electric capacitance
Authors: Pit Arjen M. , de Ruiter Riëlle , Kumar Anand , Wijnperlé Daniel , Duits Michèl H. G. , Mugele Frieder
Published: August 2015

We analyze a recently introduced approach for the sorting of aqueous drops with biological content immersed in oil, using a microfluidic chip that combines the functionality of electrowetting with the high throughput of two-phase flow microfluidics. In this electrostatic sorter, three co-planar electrodes covered by a thin dielectric layer are placed directly below the fluidic channel. Switching the potential of the central electrode creates an electrical guide that leads the drop to the desired outlet. The generated force, which deflects the drop, can be tuned via the voltage. The working principle is based on a contrast in conductivity between the drop and the continuous phase, which ensures successful operation even for drops of highly conductive biological media like phosphate buffered saline. Moreover, since the electric field does not penetrate the drop, its content is protected from electrical currents and Joule heating. A simple capacitive model allows quantitative prediction of the electrostatic forces exerted on drops. The maximum achievable sorting rate is determined by a competition between electrostatic and hydrodynamic forces. Sorting speeds up to 1200 per second are demonstrated for conductive drops of 160 pl in low viscosity oil.
Note: Compact and light displacement sensor for a precision measurement system in large motion
Authors: Lee Sang Heon
Published: August 2015

We developed a compact and light displacement sensor applicable to systems that require wide range motions of its sensing device. The proposed sensor utilized the optical pickup unit of the optical disk drive, which has been used applied to atomic force microscopy (AFM) because of its compactness and lightness as well as its high performance. We modified the structure of optical pickup unit and made the compact sensor driver attachable to a probe head of AFM to make large rotation. The feasibilities of the developed sensor for a general probe-moving measurement device and for probe-rotating AFM were verified. Moreover, a simple and precise measurement of alignment between centers of rotator and probe tip in probe-rotation AFM was experimentally demonstrated using the developed sensor.