bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals
Authors: Wang Chun-Ta , Chen Chun-Wei , Yang Tzu-Hsuan , Nys Inge , Li Cheng-Chang , Lin Tsung-Hsien , Neyts Kristiaan , Beeckman Jeroen
Published: January 2018

Selection of the bandedge lasing mode of a photonic crystal laser has been realized in a fluorescent dye doped chiral nematic liquid crystal by exerting electrical control over the mode competition. The bandedge lasing can be reversibly switched from the short-wavelength edge mode to the long-wavelength edge mode by applying a voltage of only 20 V, without tuning the bandgap. The underlying mechanism is the field-induced change in the order parameter of the fluorescent dye in the liquid crystal. The orientation of the transition dipole moment determines the polarization state of the dye emission, thereby promoting lasing in the bandedge mode that favors the emission polarization. Moreover, the dynamic mode-selection capability is retained upon polymer-stabilizing the chiral nematic liquid crystal laser. In the polymer-stabilized system, greatly improved stability and lasing performance are observed.
High speed parallel spectral-domain OCT using spectrally encoded line-field illumination
Authors: Lee Kye-Sung , Hur Hwan , Bae Ji Yong , Kim I Jong , Kim Dong Uk , Nam Ki-Hwan , Kim Geon-Hee , Chang Ki Soo
Published: January 2018

We report parallel spectral-domain optical coherence tomography (OCT) at 500 000 A-scan/s. This is the highest-speed spectral-domain (SD) OCT system using a single line camera. Spectrally encoded line-field scanning is proposed to increase the imaging speed in SD-OCT effectively, and the tradeoff between speed, depth range, and sensitivity is demonstrated. We show that three imaging modes of 125k, 250k, and 500k A-scan/s can be simply switched according to the sample to be imaged considering the depth range and sensitivity. To demonstrate the biological imaging performance of the high-speed imaging modes of the spectrally encoded line-field OCT system, human skin and a whole leaf were imaged at the speed of 250k and 500k A-scan/s, respectively. In addition, there is no sensitivity dependence in the B-scan direction, which is implicit in line-field parallel OCT using line focusing of a Gaussian beam with a cylindrical lens.
Experimental demonstration of angle-independent gaps in one-dimensional photonic crystals containing layered hyperbolic metamaterials and dielectrics at visible wavelengths
Authors: Wu Feng , Lu Guang , Xue Chunhua , Jiang Haitao , Guo Zhiwei , Zheng Minjia , Chen Chaoxin , Du Guiqiang , Chen Hong
Published: January 2018

Photonic gaps are the core of photonic crystals in the manipulation of light. However, in conventional photonic crystals composed of two types of dielectrics, the photonic gaps strongly depend on the angle of incidence, which limits their applications. In this Letter, we present the experimental demonstration of angle-independent gaps in the visible wavelength range in one-dimensional photonic crystals composed of layered hyperbolic metamaterials (HMMs) and dielectrics. HMMs with anomalous wave-vector dispersion can tune the propagating phase of light to an unprecedented extent that usual dielectrics cannot attain. The HMM is mimicked by the layered titanium dioxide and silver with a subwavelength unit cell. Based on the phase-variation compensation effect between the HMM and the dielectric, an angle-independent gap is experimentally realized, which agrees well with the simulated one. This angle-independent gap is very useful in the design of photonic devices such as omnidirectional reflectors with fixed bandwidth or all-angle filters.
Tau induces blood vessel abnormalities and angiogenesis-related gene expression in P301L transgenic mice and human Alzheimer’s disease
Authors: Bennett Rachel E. , Robbins Ashley B. , Hu Miwei , Cao Xinrui , Betensky Rebecca A. , Clark Tim , Das Sudeshna , Hyman Bradley T.
Published: January 2018

Significance

This work provides evidence that the protein tau induces changes in blood vessels distinct from the effects of amyloid beta on vasculature and indicates a previously unknown pathway by which pathological tau may accelerate cognitive decline in Alzheimer’s disease.
Molecular clutch drives cell response to surface viscosity
Authors: Bennett Mark , Cantini Marco , Reboud Julien , Cooper Jonathan M. , Roca-Cusachs Pere , Salmeron-Sanchez Manuel
Published: January 2018

Cell response to matrix rigidity has been explained by the mechanical properties of the actin-talin-integrin-fibronectin clutch. Here the molecular clutch model is extended to account for cell interactions with purely viscous surfaces (i.e., without an elastic component). Supported lipid bilayers present an idealized and controllable system through which to study this concept. Using lipids of different diffusion coefficients, the mobility (i.e., surface viscosity) of the presented ligands (in this case RGD) was altered by an order of magnitude. Cell size and cytoskeletal organization were proportional to viscosity. Furthermore, there was a higher number of focal adhesions and a higher phosphorylation of FAK on less-mobile (more-viscous) surfaces. Actin retrograde flow, an indicator of the force exerted on surfaces, was also seen to be faster on more mobile surfaces. This has consequential effects on downstream molecules; the mechanosensitive YAP protein localized to the nucleus more on less-mobile (more-viscous) surfaces and differentiation of myoblast cells was enhanced on higher viscosity. This behavior was explained within the framework of the molecular clutch model, with lower viscosity leading to a low force loading rate, preventing the exposure of mechanosensitive proteins, and with a higher viscosity causing a higher force loading rate exposing these sites, activating downstream pathways. Consequently, the understanding of how viscosity (regardless of matrix stiffness) influences cell response adds a further tool to engineer materials that control cell behavior.
Modular origins of biological electron transfer chains
Authors: Raanan Hagai , Pike Douglas H. , Moore Eli K. , Falkowski Paul G. , Nanda Vikas
Published: January 2018

Significance

There are no physical fossils of the original proteins at the beginning of life on Earth and phylogenetic approaches that infer the nature of the ancestral proteins from sequences and/or structures of extant molecules are of limited use over long time scales (e.g., billions of years). We analyzed the structures of proteins containing transition-metal cofactors, and identified four structural modules that comprise the diverse family of oxidoreductases, molecular nanomachines that are critical for electron transfer reactions that form the energetic basis of life. These structural modules are, in effect, relict “building blocks” of life that have descended through time with only minor modifications.
Context-dependent functions of angiopoietin 2 are determined by the endothelial phosphatase VEPTP
Authors: Souma Tomokazu , Thomson Benjamin R. , Heinen Stefan , Anna Carota Isabel , Yamaguchi Shinji , Onay Tuncer , Liu Pan , Ghosh Asish K. , Li Chengjin , Eremina Vera , Hong Young-Kwon , Economides Aris N. , Vestweber Dietmar , Peters Kevin G. , Jin Jing , Quaggin Susan E.
Published: January 2018

Significance

Reducing vascular leakage and stabilizing the endothelium through activation of the angiopoietin (ANGPT)–TIE2 receptor tyrosine kinase pathway is a promising therapeutic strategy for vascular diseases. ANGPT2 is one of two major ligands for the TIE2 receptor. Uniquely, ANGPT2 possesses an agonistic role in lymphatic endothelium, but acts as a competitive antagonist in blood endothelium. The molecular basis for the opposing actions of ANGPT2 in these two vascular beds is poorly understood. Here we demonstrate that the absence of VEPTP expression in the lymphatic endothelium confers an agonist function of ANGPT2 on TIE2 receptor, but VEPTP expression in blood endothelium abrogates its activity. Our findings provide mechanistic insights needed to advance therapeutic targeting of this pathway.
IL-1β enables CNS access to CCR2
hi
monocytes and the generation of pathogenic cells through GM-CSF released by CNS endothelial cells
Authors: Paré Alexandre , Mailhot Benoit , Lévesque Sébastien A. , Juzwik Camille , Ignatius Arokia Doss Prenitha Mercy , Lécuyer Marc-André , Prat Alexandre , Rangachari Manu , Fournier Alyson , Lacroix Steve
Published: January 2018

Significance

Multiple sclerosis (MS) is a neuroinflammatory disease characterized by demyelinating plaques in the brain and spinal cord, causing progressive loss of functions. While the causes of MS remain undefined, treatments that target immune cells or their functions greatly improve the clinical outcome. Our laboratory has previously shown that production of the inflammatory cytokine interleukin (IL)-1β by myeloid cells is required for the development of experimental autoimmune encephalomyelitis (EAE), an MS model. Here, we show that activation of central nervous system (CNS) endothelial cells by IL-1β enables inflammatory monocytes to enter the CNS and differentiate into antigen-presenting cells. Additionally, we demonstrate that factors released from the interaction between IL-1β–producing myeloid cells and autoreactive CD4
+
T cells are toxic to neurons.
Sporadic on/off switching of HTLV-1 Tax expression is crucial to maintain the whole population of virus-induced leukemic cells
Authors: Mahgoub Mohamed , Yasunaga Jun-ichirou , Iwami Shingo , Nakaoka Shinji , Koizumi Yoshiki , Shimura Kazuya , Matsuoka Masao
Published: January 2018

Viruses causing chronic infection artfully manipulate infected cells to enable viral persistence in vivo under the pressure of immunity. Human T-cell leukemia virus type 1 (HTLV-1) establishes persistent infection mainly in CD4+ T cells in vivo and induces leukemia in this subset. HTLV-1–encoded Tax is a critical transactivator of viral replication and a potent oncoprotein, but its significance in pathogenesis remains obscure due to its very low level of expression in vivo. Here, we show that Tax is expressed in a minor fraction of leukemic cells at any given time, and importantly, its expression spontaneously switches between on and off states. Live cell imaging revealed that the average duration of one episode of Tax expression is ∼19 hours. Knockdown of Tax rapidly induced apoptosis in most cells, indicating that Tax is critical for maintaining the population, even if its short-term expression is limited to a small subpopulation. Single-cell analysis and computational simulation suggest that transient Tax expression triggers antiapoptotic machinery, and this effect continues even after Tax expression is diminished; this activation of the antiapoptotic machinery is the critical event for maintaining the population. In addition, Tax is induced by various cytotoxic stresses and also promotes HTLV-1 replication. Thus, it seems that Tax protects infected cells from apoptosis and increases the chance of viral transmission at a critical moment. Keeping the expression of Tax minimal but inducible on demand is, therefore, a fundamental strategy of HTLV-1 to promote persistent infection and leukemogenesis.
Establishment of the early cilia preassembly protein complex during motile ciliogenesis
Authors: Horani Amjad , Ustione Alessandro , Huang Tao , Firth Amy L. , Pan Jiehong , Gunsten Sean P. , Haspel Jeffrey A. , Piston David W. , Brody Steven L.
Published: January 2018

Significance

Motile cilia preassembly proteins processing dynein motor proteins have been identified in patients with motile cilia dysfunction. However, the exact function and interaction of these proteins are not understood. Using primary airway cell culture and regulated induced pluripotent stem cell culture, we provide a roadmap for preassembly protein expression, showing that HEATR2 is the first preassembly protein to appear, emerging early in ciliogenesis and preceding known regulatory factors. HEATR2, SPAG1, and DNAAF2 colocalize within previously unrecognized cytoplasmic foci to form an early preassembly complex. The findings suggest that a lead scaffold structure essential for motile cilia function is destroyed by proteostasis in HEATR2 mutants, leading to degradation of the whole preassembly complex and identifying the cellular mechanism for disease.
Precipitation formation from orographic cloud seeding
Authors: French Jeffrey R. , Friedrich Katja , Tessendorf Sarah A. , Rauber Robert M. , Geerts Bart , Rasmussen Roy M. , Xue Lulin , Kunkel Melvin L. , Blestrud Derek R.
Published: January 2018

Throughout the western United States and other semiarid mountainous regions across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water, while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of cloud seeding as a way to increase winter snowfall, thereby shifting the balance between water supply and demand. Little direct scientific evidence exists that confirms even the basic physical hypothesis upon which cloud seeding relies. The intent of glaciogenic seeding of orographic clouds is to introduce aerosol into a cloud to alter the natural development of cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic seeding. These data, by themselves, do not address the question of cloud seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic cloud seeding aerosol into supercooled liquid orographic clouds.
Genetic and epigenetic alterations in normal tissues have differential impacts on cancer risk among tissues
Authors: Yamashita Satoshi , Kishino Takayoshi , Takahashi Takamasa , Shimazu Taichi , Charvat Hadrien , Kakugawa Yasuo , Nakajima Takeshi , Lee Yi-Chia , Iida Naoko , Maeda Masahiro , Hattori Naoko , Takeshima Hideyuki , Nagano Reiko , Oda Ichiro , Tsugane Shoichiro , Wu Ming-Shiang , Ushijima Toshikazu
Published: January 2018

Genetic and epigenetic alterations are both involved in carcinogenesis, and their low-level accumulation in normal tissues constitutes cancer risk. However, their relative importance has never been examined, as measurement of low-level mutations has been difficult. Here, we measured low-level accumulations of genetic and epigenetic alterations in normal tissues with low, intermediate, and high cancer risk and analyzed their relative effects on cancer risk in the esophagus and stomach. Accumulation of genetic alterations, estimated as a frequency of rare base substitution mutations, significantly increased according to cancer risk in esophageal mucosae, but not in gastric mucosae. The mutation patterns reflected the exposure to lifestyle risk factors. In contrast, the accumulation of epigenetic alterations, measured as DNA methylation levels of marker genes, significantly increased according to cancer risk in both tissues. Patients with cancer (high-risk individuals) were precisely discriminated from healthy individuals with exposure to risk factors (intermediate-risk individuals) by a combination of alterations in the esophagus (odds ratio, 18.2; 95% confidence interval, 3.69–89.9) and by only epigenetic alterations in the stomach (odds ratio, 7.67; 95% confidence interval, 2.52–23.3). The relative importance of epigenetic alterations upon genetic alterations was 1.04 in the esophagus and 2.31 in the stomach. The differential impacts among tissues will be critically important for effective cancer prevention and precision cancer risk diagnosis.
Increased thermogenesis by a noncanonical pathway in ANGPTL3/8-deficient mice
Authors: Banfi Serena , Gusarova Viktoria , Gromada Jesper , Cohen Jonathan C. , Hobbs Helen H.
Published: January 2018

Significance

White adipose tissue (WAT) serves as an energy reservoir during fasting and is replenished with fatty acids from circulating triglycerides upon refeeding. We showed previously that postprandial partitioning of fatty acids between oxidative and storage tissues is mediated by angiopoietin-like proteins 3 (A3) and 8 (A8). Here, we show that disruption of both
Angptl3
and
Angptl8
in mice causes striking alterations in energy metabolism: reduced fat mass, hyperthermia, increased metabolic rate, and beiging of subcutaneous WAT. The hypermetabolic features of the
A3

−/−

A8

−/−

mice were most pronounced in fed animals, and attenuated with fasting and β3-adrenergic receptor blockade. These data indicate that A3 and A8 promote efficient energy utilization by tissues and limit the increase in energy expenditure associated with food intake.
Nonsense-mediated mRNA decay factors cure most [PSI+] prion variants
Authors: Son Moonil , Wickner Reed B.
Published: January 2018

Significance

The [PSI+] prion (infectious protein) is an amyloid (filamentous polymer) of the Sup35 protein, producing detrimental effects on yeast. We find that at their normal expression levels the core components of nonsense-mediated mRNA decay for mRNA quality control, Upf1p, Upf2p, and Upf3p, block the propagation of most new [PSI+] prion variants. The curing mechanism relies upon both Sup35p-binding by each Upf protein and by the trimeric Upf complex. Our results support the notion that normal protein–protein interactions prevent abnormal interactions.
Assembly and ecological function of the root microbiome across angiosperm plant species
Authors: Fitzpatrick Connor R. , Copeland Julia , Wang Pauline W. , Guttman David S. , Kotanen Peter M. , Johnson Marc T. J.
Published: January 2018

Across plants and animals, host-associated microbial communities play fundamental roles in host nutrition, development, and immunity. The factors that shape host–microbiome interactions are poorly understood, yet essential for understanding the evolution and ecology of these symbioses. Plant roots assemble two distinct microbial compartments from surrounding soil: the rhizosphere (microbes surrounding roots) and the endosphere (microbes within roots). Root-associated microbes were key for the evolution of land plants and underlie fundamental ecosystem processes. However, it is largely unknown how plant evolution has shaped root microbial communities, and in turn, how these microbes affect plant ecology, such as the ability to mitigate biotic and abiotic stressors. Here we show that variation among 30 angiosperm species, which have diverged for up to 140 million years, affects root bacterial diversity and composition. Greater similarity in root microbiomes between hosts leads to negative effects on plant performance through soil feedback, with specific microbial taxa in the endosphere and rhizosphere potentially affecting competitive interactions among plant species. Drought also shifts the composition of root microbiomes, most notably by increasing the relative abundance of the Actinobacteria. However, this drought response varies across host plant species, and host-specific changes in the relative abundance of endosphere
Streptomyces
are associated with host drought tolerance. Our results emphasize the causes of variation in root microbiomes and their ecological importance for plant performance in response to biotic and abiotic stressors.
Early hominids may have been weed species
Authors: Meindl Richard S. , Chaney Morgan E. , Lovejoy C. Owen
Published: January 2018

Significance

Earliest hominids demonstrate major differences from fundamental behaviors typical of other primates. These included upright walking, a reduction in canine dimorphism, and unusual demographic success. All three were likely parts of a comprehensive adaptive complex that was also unlike that of any other primate and likely reflect a novel social structure. When primate “weed species,” such as some macaques, are examined for those key behavioral features most responsible for their unusual great demographic success, an irregular but robust elevation of female survivorship emerges as key. It is likely that a similar adaptation characterized earliest hominids such as
Australopithecus
.
Extension problem of subset-controlled quasimorphisms
Authors: Kawasaki Morimichi
Published: January 2018

Let

(
G
,
H
)

(G,H)

be
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="left-parenthesis normal upper H normal a normal m left-parenthesis double-struck upper R Superscript 2 n Baseline right-parenthesis comma normal upper H normal a normal m left-parenthesis double-struck upper B Superscript 2 n Baseline right-parenthesis right-parenthesis">

(

H
a
m

(

R

2
n

)
,

H
a
m

(

B

2
n

)
)

(\mathrm {Ham}(\mathbb {R}^{2n}),\mathrm {Ham}(\mathbb {B}^{2n}))

or

(

B
∞

,

B
n

)

(B_\infty ,B_n)

. We conjecture that any semi-homogeneous subset-controlled quasimorphism on

[
G
,
G
]

[G,G]

can be extended to a homogeneous subset-controlled quasimorphism on

G
G

and also give a theorem supporting this conjecture by using a Bavard-type duality theorem on conjugation invariant norms.
E. colitranslation strategies differ across nutrient conditions
Authors: Li Sophia Hsin-Jung , Li Zhiyuan , Park Junyoung O. , King Christopher G. , Rabinowitz Joshua D. , Wingreen Ned S. , Gitai Zemer
Published: January 2018

For cells to grow faster they must increase their protein production rate. Microorganisms have traditionally been thought to accomplish this increase by producing more ribosomes to enhance protein synthesis capacity, leading to the linear relationship between ribosome level and growth rate observed under most growth conditions previously examined. Past studies have suggested that this linear relationship represents an optimal resource allocation strategy for each growth rate, independent of any specific nutrient state. Here we investigate protein production strategies in continuous cultures limited for carbon, nitrogen, and phosphate, which differentially impact substrate supply for protein versus nucleic acid metabolism. Unexpectedly, we find that at slow growth rates,E. coliachieves the same protein production rate using three different strategies under the three different nutrient limitations. Upon phosphate (P) limitation, translation is slow due to a particularly low abundance of ribosomes, which are RNA-rich and thus particularly costly for phosphorous-limited cells. In nitrogen (N) limitation, translation is slowed by limited glutamine and stalling at glutamine codons, resulting is slow elongation. In carbon (C) limitation, translation is slowed by accumulation of inactive ribosomes not bound to mRNA. These extra ribosomes enable rapid growth acceleration upon nutrient upshift. Thus, bacteria tune ribosome usage across different limiting nutrients to enable balanced nutrient-limited growth while also preparing for future nutrient upshifts.
Parallel holographic illumination enables sub-millisecond two-photon optogenetic activation in mouse visual cortex in vivo
Authors: Chen I-Wen , Ronzitti Emiliano , Lee Brian R. , Daigle Tanya L. , Zeng Hongkui , Papagiakoumou Eirini , Emiliani Valentina
Published: January 2018

Selective control of action potential generation in individual cells from a neuronal ensemble is desirable for dissecting circuit mechanisms underlying perception and behavior. Here, by using two-photon (2P) temporally focused computer-generated holography (TF-CGH), we demonstrate optical manipulation of neuronal excitability at the supragranular layers of anesthetized mouse visual cortex. Utilizing amplified laser-pulses delivered via a localized holographic spot, our optical system achieves suprathreshold activation by exciting either of the three optogenetic actuators, ReaChR, CoChR or ChrimsonR, with brief illumination (≤ 10 ms) at moderate excitation power ((in average ≤ 0.2 mW/µm2 corresponding to ≤ 25 mW/cell). Using 2P-guided whole-cell or cell-attached recordings in positive neurons expressing respective opsin in vivo, we find that parallel illumination induces spikes of millisecond temporal resolution and sub-millisecond precision, which are preserved upon repetitive illuminations up to tens of Hz. Holographic stimulation thus enables temporally precise optogenetic activation independently of opsin’s channel kinetics. Furthermore, we demonstrate that parallel optogenetic activation can be combined with functional imaging for all-optical control of a neuronal sub-population that co-expresses the photosensitive opsin ReaChR and the calcium indicator GCaMP6s. Parallel optical control of neuronal activity with cellular resolution and millisecond temporal precision should be advantageous for investigating neuronal connections and further yielding causal links between connectivity, microcircuit dynamics, and brain functions.

Significance statement

Recent development of optogenetics allows probing the neuronal microcircuit with light by optically actuating genetically-encoded light-sensitive opsins expressed in the target cells. Here, we apply holographic light shaping and temporal focusing to simultaneously deliver axially-confined holographic patterns to opsin-positive cells situated in the living mouse cortex. Parallel illumination efficiently induces action potentials with high temporal resolution and precision for three opsins of different kinetics. We demonstrated all-optical experiments by extending the parallel optogenetic activation at low intensity to multiple neurons and concurrently monitoring their calcium dynamics. These results demonstrate fast and temporally precise in vivo control of a neuronal sub-population, opening new opportunities to reveal circuit mechanisms underlying brain functions.
Optimising the multiplicative AF model parameters for AA7075 cyclic plasticity and fatigue simulation
Authors: Agius Dylan , Kajtaz Mladenko , Kourousis Kyriakos I. , Wallbrink Chris , Hu Weiping
Published: January 2018

Purpose

This study presents the improvements of the multicomponent Armstrong–Frederick model with multiplier (MAFM) performance through a numerical optimisation methodology available in a commercial software. Moreover, this study explores the application of a multiobjective optimisation technique for the determination of the parameters of the constitutive models using uniaxial experimental data gathered from aluminium alloy 7075-T6 specimens. This approach aims to improve the overall accuracy of stress–strain response, for not only symmetric strain-controlled loading but also asymmetrically strain- and stress-controlled loading.

Design/methodology/approach

Experimental data from stress- and strain-controlled symmetric and asymmetric cyclic loadings have been used for this purpose. The analysis of the influence of the parameters on simulation accuracy has led to an adjustment scheme that can be used for focused optimisation of the MAFM model performance. The method was successfully used to provide a better understanding of the influence of each model parameter on the overall simulation accuracy.

Findings

The optimisation identified an important issue associated with competing ratcheting and mean stress relaxation objectives, highlighting the issues with arriving at a parameter set that can simulate ratcheting and mean stress relaxation for load cases not reaching at complete relaxation.

Practical implications

The study uses a strain-life fatigue application to demonstrate the importance of incorporating a technique such as the presented multiobjective optimisation method to arrive at robust parameters capable of accurately simulating a variety of transient cyclic phenomena.

Originality/value

The proposed methodology improves the accuracy of cyclic plasticity phenomena and strain-life fatigue simulations for engineering applications. This study is considered a valuable contribution for the engineering community, as it can act as starting point for further exploration of the benefits that can be obtained through material parameter optimisation methodologies for models of the MAFM class.
Comparative analysis of numerical methods for the determination of contact pattern of spiral bevel gears
Authors: Marciniec Adam , Pacana Jacek , Pisula Jadwiga Malgorzata , Fudali Pawel
Published: January 2018

Purpose

This paper aims to present a comparison of numerical methods for determining the contact pattern of Gleason-type bevel gears. The mathematical model of tooth contact analysis and the finite element method were taken into consideration. Conclusions have been drawn regarding the usefulness of the considered methods and the compatibility of results. The object of the analysis was a bevel gear characterised by an 18:43 gear ratio and arc tooth line, and manufactured according to the spiral generated modified-roll method.

Design/methodology/approach

The mathematical model of tooth contact analysis consists of both the mathematical model of tooth generating and the mathematical model of operating gear set. The first model is used to generate tooth flanks of the pinion and the ring gear in the form of grids of points. Then, such tooth surfaces are used for the tooth contact analysis performed with the other model. It corresponds to the no-load gear meshing condition. The finite element method model was built on the basis of the same tooth flanks obtained with the former model. The commercial finite element method software Abaqus was used to perform two instances of the contact analysis: a very light load, corresponding to the former no-load condition, and the operating load condition. The results obtained using the two models, in the form of the contact pattern for no-load condition, were compared. The effect of heavy load on contact pattern position, shape and size was shown and discussed.

Findings

The mathematical models correctly reproduce the shape, position and size of the contact pattern; thus, they can be reliably used to assess the quality of the bevel gear at the early stage of its design.

Practical implications

Determination of the correct geometry of the flank surfaces of the gear and pinion teeth through the observation of contact pattern is a fundamental step in designing of a new aircraft bevel gear.

Originality/value

A possibility of the independent use of the mathematical analysis of the contact pattern has been shown, which, thanks to the compatibility of the results, does not have to be verified experimentally.
Coatings characterization of Ni-based alloy applied by HVOF
Authors: Cabral Miramontes José , Pedraza Basulto Gabriela Karina , Gaona Tiburcio Citlalli , Zambrano Robledo Patricia Del Carmen , Poblano Salas Carlos Agustín , Almeraya Calderón Facundo
Published: January 2018

Purpose

The thermal spraying technique of High-Velocity Oxygen Fuel (HVOF) coating was used to deposit coatings of an alloy composed of Ni-based substrates on stainless steel AISI 304. The aim of this study was to determine the mechanical properties such as hardness and bond strength that these coatings have when the spray distance is varied, as well as the microstructure and phases formed during the thermal spray process.

Design/methodology/approach

The coatings were applied by HVOF and characterized by scanning electron microscopy, image analysis, X-ray diffraction, microhardness and bond strength to analyze the mechanical properties.

Findings

The microstructure of the coatings showed low porosity, oxide content and interface contamination in the substrate–coating interface, without the presence of unmolten particles. The microhardness values reached 600 HV for the three spray distances used and the bond strength values reached over 55 MPa.

Practical implications

The use of coatings on aircraft components is growing dramatically owing to the high costs of advanced materials and the growing lifecycle requirements for high-performance systems, which are taken into account because of the variety of coatings and complexity of environmental factors.

Originality/value

The originality of this study lies in the development of new coating materials for the manufacture and protection of various turbine components. The value is based on the development of materials and processes to be used to manufacture them.
Bayesian filtering based on solving the Fokker-Planck equation
Authors: Wang Xiaogang , Qin Wutao , Wang Yu , Cui Naigang
Published: January 2018

Purpose

This paper aims to propose Bayesian filtering based on solving the Fokker–Planck equation, to improve the accuracy of filtering in non-Gauss case. Nonlinear filtering plays an important role in many science and engineering fields for estimating the state of dynamic system, but the existing filtering algorithms are mainly used for solving the problem of Gauss system.

Design/methodology/approach

Under the Bayesian framework, the time update of this filtering is based on solving Fokker–Planck equation, while the measurement update uses the Bayes formula directly. Therefore, this novel algorithm can be applied to nonlinear, non-Gaussian estimation. To reduce the computational complexity due to standard meshing, an adaptive meshing algorithm proposed which includes the coarse meshing, significant domain determination that is generated using extended Kalman filtering and Chebyshev’s inequality theorem, and value assignment for significant domain. Simulations are conducted on a reentry body tracking problem to demonstrate the effectiveness of this novel algorithm.

Findings

In this way, finer grid points can be placed in the regions with high conditional probability density, while the grid points with low conditional probability density can be neglected. The simulation results indicate that the novel algorithm can reduce the computational burden significantly compared to the standard meshing, while achieving similar accuracy.

Practical implications

A novel Bayesian filtering based on solving the Fokker–Planck equation using adaptive meshing is proposed, and the simulations show that algorithm can reduce the computational burden significantly compared to the standard meshing, while achieving similar accuracy.

Originality/value

A novel nonlinear filtering based on solving the Fokker–Planck equation is proposed. The novel algorithm is suitable for non-Gauss system, and can achieve similar accuracy compared to the standard meshing with the significant reduction of computational burden.
An optimization approach for DAL assignments
Authors: Li Xianan , Lu Zhong , Wang Jingyi
Published: January 2018

Purpose

Development assurance level (DAL) is the measurement of the rigor of development assurance tasks performed to functions or items. The DAL assignment is an important process of aircraft system development that can make the reliability and safety of the system stay at acceptable levels. This paper aims to propose an optimization approach for the DAL assignments to minimize the development cost of aircraft systems.

Design/methodology/approach

The mathematical model for the DAL assignment optimization has been developed on the basis of the given expressions of objective function and constraints. In addition, a hybrid algorithm model synthesizing the advantages of genetic algorithm (GA) and Tabu search (TS) has been proposed to solve the optimization problem of the DAL assignment.

Findings

The results of the case study show that the proposed hybrid algorithm is more efficient and effective than the exhaustive method as well as the pure GA.

Practical implications

The proposed approach can be applied in the development of aircraft systems, and it has great significance in minimizing the development cost as well as keeping the system reliability and safety at an acceptable level.

Originality/value

The constrained optimization method has been applied in the DAL assignments, the corresponding mathematical model has been built and a hybrid evolutionary algorithm has been proposed to solve the optimization problem.
Bevel gears tooth contact pattern verification
Authors: Trzewik Pawel , Skawinski Piotr
Published: January 2018

Purpose

This paper aims to create an application to support spiral bevel gear contact pattern verification in the computer aided design (CAD) system to speed up the selection of technological setups for the cutting machine by finding these in the virtual environment at the design level.

Design/methodology/approach

This paper presents an application which has been created to simulate a pattern check on spiral bevel gears in the virtual environment. The pattern check is conducted on the CAD models obtained from the cutting simulation in the CAD system using technological settings calculated by the KONTEPS system. Check of the contact pattern in the virtual environment works in the same way as in the real production process. The application has been written in C# programming language and run in the NX open environment in the UG NX.

Findings

This paper shows the possibilities of how the CAD system can be used at the design level of spiral bevel gears to verify an unloaded tooth contact pattern position for applied technological setups for dedicated cutting machine.

Practical implications

This paper describes an application that has the possibility to be implemented in small companies which produce small lots of gear sets and help to decrease the time for setting a cutting machine.

Originality/value

This paper addresses the needs to find new technologies to improve the design process of the spiral bevel gears.
Analytical study and simulation of a transformer-less photovoltaic grid-connected inverter with a delta-type tri-direction clamping cell for leakage current elimination
Authors: Jalilzadeh Tohid , Tarafdar Hagh Mehrdad , Sabahi Mehran
Published: January 2018

Purpose

This paper aims to propose a new transformer-less inverter structure to reduce the common-mode leakage current in grid-connected photovoltaic (PV) systems.

Design/methodology/approach

The proposed circuit structure is the same as the conventional full-bridge inverter with three additional power switches in a triangular structure. These three power switches are between the bridge and the output filter, and they mitigate the common-mode leakage current flowing toward the PV panels’ capacitors. The common-mode leakage current mitigation is done through the three-direction clamping cell (TDCC) concept. By clamping the common-mode voltage to the middle voltage of the DC-link capacitors, the leakage current and the total harmonic distortion (THD) of the injected current to the grid is effectively reduced. Therefore, the efficiency is improved.

Findings

The switching modes and the control method are introduced. A comparison is carried out between the proposed structure and other solutions in the literature. The proposed topology and its respective control method are simulated by PSCAD/EMTDC software. The simulation results validate the advantages of the presented structure such as clamping the common-mode voltage and reducing leakage current and THD of injected current to the grid.

Originality/value

Presenting a single phase-improved inverter structure with low-leakage current for grid-connected PV power systems represents a significant original contribution to this work. The proposed structure can inject a sinusoidal current with low THD to the AC grid, and the power factor is unity on the AC side. In the half positive cycle, one of the switches in the TDCC is turned off under zero current. Besides, one of the other switches in TDCC is turned on with zero voltage and, therefore, its turn-on switching losses are zero. The efficiency of the proposed topology is high because of the reduction of leakage current and power losses. Accordingly, the presented topology can be a good solution to the leakage current elimination.
Predicting the unstable period-1 orbit (UPO-1) of DC–DC converters by extracting harmonic content
Authors: Chen Xi , Chen Yanfeng , Zhang Bo , Qiu Dongyuan , Li Zi
Published: January 2018

Purpose

This study aims to predict the unstable period-1 orbit (UPO-1) of DC–DC converters and find analytical expressions to describe it.

Design/methodology/approach

Nonlinear dynamical phenomena of a peak–current–mode controlled direct current–direct current (DC–DC) Boost converter are discussed briefly first. Then fast fourier transform (FFT) analysis of state variables under different dynamic states is provided, and the characteristic of the harmonic content in different states is summarized. Following these, a scientific hypothesis on the harmonic content of the UPO-1 is presented, and the Equivalent Small Parameter method is adopted then, thus analytic-form expressions of the UPO-1 can be derived.

Findings

According to results of theoretical analysis, numerical simulations and experiments, this paper illustrates that, like stable period-1 orbit, the UPO-1 is also made up of the DC component and harmonics with integer times of switching frequency.

Originality/value

This work provides an unreported approach for extracting the UPO-1 of DC–DC converters, which is mainly based on predicting the harmonic structure information of the orbit. According to experimental parts of the work, it shows that the stabilizer can be designed easier by using the proposed method. Additionally, from a broader perspective, the results could also have implications in a wide class of forced oscillation systems.
Numerical modelling on partial discharge in HVDC XLPE cable
Authors: He Miao , Hao Miao , Chen George , Chen Xin , Li Wenpeng , Zhang Chong , Wang Haitian , Zhou Mingyu , Lei Xianzhang
Published: January 2018

Purpose

High voltage direct current (HVDC) cable is an important part in the electric power transmission and distribution systems. However, very little research has been carried out on partial discharge under direct current (DC) conditions. Niemeyer’s model has been widely used under alternating current (AC) conditions. This paper aims to intend to modify the Niemeyer’s model considering both electric field and charge dynamics under DC conditions, and therefore proposes a numerical model describing partial discharge characteristics in HVDC cable.

Design/methodology/approach

This paper intends to understand partial discharge characteristics under DC conditions through numerical modelling. Niemeyer’s model that has been widely used under AC conditions has been modified, taking both electric field and charge dynamics under DC conditions into consideration. The effects of loading level or current through the conductor, cavity location and material properties on partial discharges have also been studied.

Findings

Electrical conductivity is important in determining the characteristics of partial discharge under DC conditions and discharges tend to happen in short when the cavity field exceeds the inception level under the parameter values studied in the paper.

Research limitations/implications

Building the numerical model is the purpose of the paper, and there is lack in experiment and the comparison between the simulation results and experiment.

Practical implications

The proposed model provides the numerical model describing partial discharge in HVDC cable and helps understand the partial discharge mechanism under DC voltage.

Originality/value

To the best of the author’s knowledge, this paper is a very early research on the numerical modelling work on partial discharge under DC voltage.
An energy-efficient scalar control taking core losses into account
Authors: Khoury Gabriel , Ghosn Ragi , Khatounian Flavia , Fadel Maurice , Tientcheu Mathias
Published: January 2018

Purpose

In the need to optimize the energy efficiency, control structures can have a positive effect by tracking the optimal operating point according to the speed and mechanical load of the motor. The purpose of this paper is to present an energy-efficient scalar control for squirrel-cage induction motors (IMs), taking into consideration the effect of core losses.

Design/methodology/approach

The proposed technique is based on the modification of the stator flux reference, to track the best efficiency point. The optimal flux values are computed through an improved model of the IM including core losses, then stored in a look-up table.

Findings

Simulations of the proposed scalar control are carried out, and results show the efficiency improvement when the flux is optimized especially at low load cases. Results were validated experimentally on two motors compliant with different efficiency standards.

Practical implications

The proposed approach can be used in several fields and applications using the scalar-controlled IM with a proper implementation in variable speed drives, as in the cases of pumps, compressors and blowers.

Originality/value

The proposed technique is compared to existing optimization methods in literature, and the results show an improvement in the dynamic performance and in the response delays. The approach is also compared to an optimization technique used in industries like Leroy-Somer for variable speed drives, and efficiency improvements are shown.
Design and simulation of electro-thermal compliant MEMS logic gates
Authors: P. Pandiyan , G. Uma , M. Umapathy
Published: January 2018

Purpose

The purpose of this paper is to design an out-of-plane micro electro-thermal-compliant actuator based logic gates which work analogously to complementary metal oxide semiconductor (CMOS) based logic gates. The proposed logic gates used a single-bit mechanical micro ETC actuator per logic instead of using 6-14 individual transistors as in CMOS.

Design/methodology/approach

A complete analytical modelling is performed on a single ETC vertical actuator, and a relation between the applied voltage and the out-of-plane deflection is derived. Its coupled electro-thermo-mechanical analysis is carried out using micro electro mechanical system (MEMS) CAD tool CoventorWare to illustrate its performance.

Findings

This paper reports analytical and numerical simulation of basic MEMS ETC actuator-based logic gates. The proposed logic gate operates on 5 V, which suits well with conventional CMOS logic, which in turn reduces the power consumption of the device.

Originality/value

The proposed logic gates uses a single-bit MEMS ETC actuator per logic instead of using more transistors as in CMOS. The unique feature of this proposed logic gates is that the basic mechanical ETC actuator is customized in its structure to function as specific logic gates depending upon the given inputs.