bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability assessment of a multi‐state distribution system with microgrids based on an accelerated Monte‐Carlo method
Authors: Yan Tao , Tang Wei , Wang Yue , Zhang Xianliang
Published: April 2018

For the reliability assessment of a distribution system with microgrids (MGs), considerable computation time has to be cost to ensure convergence of an applied Monte‐Carlo method (MCM) to estimating indices of interest, in the context of adopting multi‐state models of constituent components. Towards achieving an efficient and accurate reliability assessment as much as possible, multi‐state models of distributed generation resources, especially the battery energy storage system, are proposed. Based on the proposed models, effect analysis of a given sampled MG state is conducted in a proposed analytical manner. Moreover, an accelerated MCM nesting the proposed effect analysis methodology is also presented, dedicated to reliability evaluation of a resulting multi‐state distribution system from the multi‐state constituent components. Case studies on a modified IEEE‐RBTS Bus6 F4 system demonstrate the effectiveness of the proposed method, against the plain MCM. In addition, impact of an important parameter, termed total state number of state‐of‐charge, on the convergence and speed of the proposed method has been fully analysed.
Orthogonal gradient measurement matrix optimisation method
Authors: Pan Jinfeng , Shen Jin , Gao Mingliang , Yin Liju , Liu Faying , Zou Guofeng
Published: April 2018

The optimisation of measurement matrix that is within the compressive sensing framework is considered in this study. Based on the fact that an information factor with smaller mutual coherence performs better, the gradient measurement matrix optimisation method is improved by an orthogonal search direction revision factor. This algorithm updates the approximation of ideal Gram matrix of information operator and the measurement matrix alternatingly. Using measurement matrix and sparse basis to represent the Gram matrix, the measurement matrix is optimised by the gradient algorithm, in which an orthogonal gradient search direction revision factor is proposed and utilised to further improve the performance of measurement matrix. This orthogonal factor is computed by the Cayley transform of a real skew symmetric matrix that is related to the gradient and the measurement matrix. Results of several experiments show that compared with the initial random matrix, the optimised measurement matrix can lead to better signal reconstruction quality.
Hand gesture recognition using DWT and F‐ratio based feature descriptor
Authors: Sahoo Jaya Prakash , Ari Samit , Ghosh Dipak Kumar
Published: April 2018

This study demonstrates the development of vision based static hand gesture recognition system using web camera in real‐time applications. The vision based static hand gesture recognition system is developed using the following steps: preprocessing, feature extraction and classification. The preprocessing stage consists of illumination compensation, segmentation, filtering, hand region detection and image resize. This study proposes a discrete wavelet transform (DWT) and Fisher ratio (F‐ratio) based feature extraction technique to classify the hand gestures in an uncontrolled environment. This method is not only robust towards distortion and gesture vocabulary, but also invariant to translation and rotation of hand gestures. A linear support vector machine is used as a classifier to recognise the hand gestures. The performance of the proposed method is evaluated on two standard public datasets and one indigenously developed complex background dataset for recognition of hand gestures. All above three datasets are developed based on American Sign Language (ASL) hand alphabets. The experimental result is evaluated in terms of mean accuracy. Two possible real‐time applications are conducted, one is for interpretation of ASL sign alphabets and another is for image browsing.
Low profile pattern‐switchable multibeam antenna consisting of four L‐shaped microstrip lines
Authors: Zhang Wei , Pal Arpan , Mehta Amit , Mirshekar‐Syahkal Dariush , Nakano Hisamatsu
Published: April 2018

A multibeam antenna consisting of a set of four L‐shaped microstrip line sections is presented for pattern switchable applications. A planar electromagnetic band gap substrate is implemented to reduce the antenna profile to λ2.45/35, where λ2.45 is the free space wavelength at a design frequency of 2.45 GHz. An impedance matching network is integrated on the lowest layer below a ground plane. The microstrip lines have a resonant frequency of 2.45 GHz and are excited separately. When one of the strips is excited, the antenna generates a tilted beam with a gain of 8.6 dBi. By switching the excitation strip sequentially, a full azimuth beam steering is achieved. When the antenna is located above a large conducting reflector, the antenna maintains its performance. Thus, the antenna is a candidate for moving objects with high speed internet and vehicular tracking.
Improved spiral antenna with a new semi‐fractal reflector for short‐range sensing
Authors: Ranjbaran Sayed Mohammad Husain , Mohanna Shahram
Published: April 2018

An improved meandered spiral antenna with a new semi‐fractal reflector is designed and fabricated. It is considered as a unidirectional circular polarised broadband antenna having high gain. To improve the impedance bandwidth, the top layer of the antenna is shaped as equiangular Archimedean lines which its outer area meanders. The reflector consists of many fractal hexagonal shape cells. It is implemented at the back of the spiral antenna in order to improve the gain and circular polarisation. The simulated and measured results indicated that the antenna covers the impedance bandwidth of 446% within the frequency region of 0.8–4.37 GHz having the gain of 7.5–13 dBiC. The antenna is designed to be employed in positioning and short‐range sensing systems.
Low‐cost coaxial DFB LD transmitter optical subassembly for 25 Gb/s NRZ and 50 Gb/s PAM‐4 transmissions
Authors: Jou Jau‐Ji , Shih Tien‐Tsorng , Su Zhe‐Xian , Liao Chuan‐Yu , Wang Wei
Published: April 2018

Here, a directly modulated coaxial distributed feedback (DFB) laser diode (LD) transmitter optical subassembly (TOSA) module is proposed for 25 Gb/s non‐return‐to‐zero (NRZ) and 50 Gb/s four‐level pulse amplitude modulation (PAM‐4) transmissions. A low‐cost TO‐56 header was used in the DFB LD TOSA package. The high‐frequency performance of the coaxial 1310 nm DFB LD TOSA module was simulated and analysed. The simulated frequency response can correspond with the measured result, and the 3 dB bandwidth was 19 GHz. In the back‐to‐back and 10 km signal mode fibre transmissions, 25 Gb/s NRZ and 50 Gb/s PAM‐4 eye diagrams of the DFB LD TOSA were measured. Clear 25 Gb/s NRZ and 50 Gb/s PAM‐4 eye openings can be observed. For 25 Gb/s NRZ transmissions, the received sensitivity was −11.8 dBm under a bit error rate (BER) of 10−12. For 50 Gb/s PAM‐4 transmissions, the BER was estimated to be below the forward error correction threshold. The low‐cost coaxial DFB LD TOSA is suitable in 100, 200, and 400 Gb/s transmissions.
Control of a high‐voltage bidirectional dc–dc flyback converter for driving DEAs
Authors: Shagerdmootaab Ali , Pourazadi Shahram , Moallem Mehrdad , Menon Carlo
Published: April 2018

This study presents modelling and control of a high‐voltage ratio flyback converter for driving capacitive loads including smart material dielectric elastomer actuators (DEAs). These actuators find various applications including artificial muscles, optical devices, smart skin, and acoustics but require high actuation voltages. To this end, a high‐voltage bidirectional flyback converter for driving a capacitive load is studied in terms of modelling and control and applied to a DEA. The state‐space model of the converter is obtained for the capacitor charge and discharge modes when the converter operates in the continuous conduction mode and used to obtain a load voltage controller using the feedback linearisation method. The converter can be used to regenerate the capacitor charge into the dc source. The proposed hardware and control strategy was built and validated by driving DEA capacitive loads operating at high voltages around 4 kV. The experimental results are presented which validate the performance of the proposed converter and its control strategy.
Composite adaptive model predictive control for DC–DC boost converters
Authors: Po Li , Ruiyu Li , Tianying Shao , Jingrui Zhang , Zheng Fang
Published: April 2018

A composite adaptive model predictive control (MPC) scheme is proposed to mitigate model mismatches due to parameter uncertainties and disturbances in controller designs for DC–DC boost converters. First, a model‐based feedforward compensator based on a cascade proportional‐integral (PI) MPC controller was developed as a current reference to improve the dynamic response performance. Then, an observer was employed to construct an accurate model and thereby avoid overcompensation and poor prediction due to model mismatch. Finally, a finite control set MPC was implemented to select a suitable switching state with which to realise output voltage regulation. Compared with a traditional PI MPC, the proposed controller has a rapid dynamic response, and compared with an unknown offset free MPC, the proposed controller is well suited to a simplified model. The proposed methods and benefits were validated by simulations in MATLAB/Simulink and by experiments on an NI Compact RIO rapid control prototype test bench.
Near‐field reconstruction for portable wireless devices by deconvolution from input impedance changes
Authors: Horváth Bálint , Horváth Péter , Badics Zsolt , Pavó József
Published: April 2018

The near‐field validation of computational electromagnetic models of personal wireless communication devices is becoming indispensable, especially, when assessing specific absorption rate (SAR) compliance to regulatory limits by computer simulation. A possible practice for such validation is to compare measured and simulated electromagnetic field distributions in a standard flat phantom designed for SAR compliance measurements. The authors recently presented an input impedance measurement‐based validation method. They extend their scheme with a deconvolution procedure. This enables near field validation based on the reconstructed field obtained by the deconvolved measurement of the impedance change compared to the calculated . However, the reconstruction problem is inherently ill conditioned and requires numerical treatment. They demonstrate that the regularisation of the convolution matrix makes the reconstruction of the field feasible with promising error. Through examples of a 1 GHz printed inverted F and a 1.8 GHz printed monopole antenna, they show that the mean‐square error as low as 1% between the original and the reconstructed is achievable with the proposed method.
Bifurcation analysis of insulin regulated mTOR signalling pathway in cancer cells
Authors: Sriram Krishnamachari
Published: April 2018

Insulin induced mTOR signalling pathway is a complex network implicated in many types of cancers. The molecular mechanism of this pathway is highly complex and the dynamics is tightly regulated by intricate positive and negative feedback loops. In breast cancer cell lines, metformin has been shown to induce phosphorylation at specific serine sites in insulin regulated substrate of mTOR pathway that results in apoptosis over cell proliferation. The author models and performs bifurcation analysis to simulate cell proliferation and apoptosis in mTOR signalling pathway to capture the dynamics both in the presence and absence of metformin in cancer cells. Metformin is shown to negatively regulate PI3K through AMPK induced IRS1 phosphorylation and this brings about a reversal of AKT bistablity in codimension‐1 bifurcation diagram from S‐shaped, related to cell proliferation in the absence of drug metformin, to Z‐shaped, related to apoptosis in the presence of drug metformin. The author hypothesises and explains how this negative regulation acts a circuit breaker, as a result of which mTOR network favours apoptosis of cancer cells over its proliferation. The implication of reversing the shape of bistable dynamics from S to Z or vice‐versa in biological networks in general is discussed.
Numerical estimation of wavefront error breakdown in adaptive optics
Authors: Ferreira F. , Gendron E. , Rousset G. , Gratadour D.
Published: April 2018

Aims.Adaptive optics (AO) system performance is improved using post-processing techniques, such as point spread function (PSF) deconvolution. The PSF estimation involves characterization of the different wavefront (WF) error sources in the AO system. We propose a numerical error breakdown estimation tool that allows studying AO error source behavior such as their correlations. We also propose a new analytical model for anisoplanatism and bandwidth errors that were validated with the error breakdown estimation tool. This model is the first step for a complete AO residual error model that is expressed in deformable mirror space, leading to practical usage such as PSF reconstruction or turbulent parameters identification.

Methods.We have developed in the computing platform for adaptive optics systems (COMPASS) code, which is an end-to-end simulation code using graphics processing units (GPU) acceleration, an estimation tool that provides a comprehensive error breakdown by the outputs of a single simulation run. We derive the various contributors from the end-to-end simulator at each iteration step: this method provides temporal buffers of each contributor. Then, we use this tool to validate a new model of anisoplanatism and bandwidth errors including their correlation. This model is based on a statistical approach that computes the error covariance matrices using structure functions.

Results.On a SPHERE-like system, the comparison between a PSF computed from the error breakdown with a PSF obtained from classical end-to-end simulation shows that the statistics convergence limits converge very well, with a sub-percent difference in terms of Strehl ratio and ensquared energy at 5λ/Dseparation. A correlation analysis shows significant correlations between some contributors, especially WF measurement deviation error and bandwidth error due to centroid gain, and the well-known correlation between bandwidth and anisoplanatism errors is also retrieved. The model we propose for the two latter errors shows an SR and EE difference of about one percent compared to the end-to-end simulation, even if some approximations exist.
Exploring the production and depletion of lithium in the Milky Way stellar disk
Authors: Bensby Thomas , Lind Karin
Published: April 2018

Despite the recent availability of large samples of stars with high-precision Li abundances, there are many unanswered questions about the evolution of this unique element in the Galaxy and in the stars themselves. It is unclear which parameters and physical mechanisms govern Li depletion in late-type stars and if Galactic enrichment has proceeded differently in different stellar populations. With this study we aim to explore these questions further by mapping the evolution of Li with stellar mass, age, and effective temperature for Milky Way disk stars, linking the metal-poor and metal-rich regimes, and how Li differs in the thin and thick disks. We determine Li abundances for a well-studied sample of 714 F and G dwarf, turn-off, and subgiant stars in the solar neighbourhood. The analysis is based on line synthesis of the 7Li line at 6707 Å in high-resolution and high-signal-to-noise ratio echelle spectra, obtained with the MIKE, FEROS, SOFIN, UVES, and FIES spectrographs. The presented Li abundances are corrected for non-LTE effects. Out of the sample of 714 stars, we are able to determine Li abundances for 394 stars and upper limits on the Li abundance for another 121 stars. Out of 36 stars that are listed as exoplanet host stars, 18 have well-determined Li abundances and 6 have Li upper limits. Our main finding is that there are no signatures of Li production in stars associated with the thick disk. Instead the Li abundance trend is decreasing with metallicity for these thick disk stars. Significant Li production is however seen in the thin disk, with a steady increase towards super-solar metallicities. At the highest metallicities, however, around [Fe/H] ≈ +0.3, we tentatively confirm the recent discovery that the Li abundances level out. Our finding contradicts the other recent studies that found that Li is also produced in the thick disk. We find that this is likely due to the α-enhancement criteria which those studies used to define their thick disk samples. By using the more robust age criteria, we are able to define a thick disk stellar sample that is much less contaminated by thin disk stars. Furthermore, we also tentatively confirm the age-Li correlation for solar twin stars, and we find that there is no correlation between Li abundance and whether the stars have detected exoplanets or not. The major conclusion that can be drawn from this study is that no significant Li production relative to the primordial abundance took place during the first few billion years of the Milky Way, an era coinciding with the formation and evolution of the thick disk. Significant Li enrichment then took place once long-lived low-mass stars (acting on a timescale longer than SNIa) had had time to contribute to the chemical enrichment of the interstellar medium.
Analysis of hysteresis effect on the vibration behavior of AFM intelligent MC in the vicinity of sample surface by considering the size effect in air and liquid
Authors: Korayem Alireza Habibnejad , Taghizadeh Mitra , Emadi Fatemeh
Published: April 2018

Nowadays, scientists consider AFM as a powerful Nanorobot for the measurement of inter-molecular forces as well as identification and topography of sample surfaces. In order to enhance the performance of this Nanorobot, the modified couple stress (MCS) theory in the air and the liquid environment has used to reduce the error resulting from the modeling of AFM microcantilever (MC) based on classic continuum mechanic theory. In this paper, using the Hamiltonian principle and based on the Euler Bernoulli beam theory, motion equations are extracted taking into account the capillary, van der Waals and contact forces between the tip and the sample, as well as the hydrodynamic and the squeeze force in the liquid environment. Modeling is carried out for two dagger and rectangular geometries considering the geometric discontinuities due to the presence of a piezoelectric layer enclosed between the two sides of the electrode and the change in the cross-section of the MC when connecting the probe to the MC. Galerkin method is employed for the discretization of equations. In order to analyze the effects of geometry and environment on the MC vibration behavior, the time and frequency response are obtained at distances away from the surface for both MC geometries in the air and liquid environment. Comparison results suggest that the natural frequency is reduced due to the added mass of the dagger MC. This reduction is more tangible in the liquid environment because of the added mass. Also, the effect of the hysteresis phenomenon caused by the ferromagnetic property of materials is analyzed in order to approximate the theoretical model to the real model using the PI, Bouce-van and Duhem models. Surface topography is illustrated considering the hysteresis effect on rectangular and dagger MC. According to the results, the amplitude is amplified by using the three models. This amplification is higher in the PI model.
A trait database for Phytoplankton of temperate lakes
Authors: Rimet Frédéric , Druart Jean-Claude
Published: April 2018

Phytoplankton is a choice ecological indicator of lake ecological quality. Microalgae composing this biological compartment display a large diversity of morphological, physiological and ecological features, which are useful for understanding the interactions they have with other biotic and abiotic elements. Such kind of information together with classical Utermöhl phytoplankton analyses are useful for lake management and basic science. We present here a reference database of morphological (cell and colony sizes, biovolumes, mobility apparatus, colony formation), functional (functional groups of Reynolds, Padisak and Kruk, zooplankton edibility groups), physiological (trophic capacities) and ecological traits (Brettum index values) of more than 1200 taxa often observed in temperate lakes. This database, maintained since the 70’s until nowadays by the authors of this paper is now realized open access in Zenodo (https://zenodo.org; DOI: 10.5281/zenodo.1164834) and also as supplementary material on the journal website. The paper presents an overview of its content.
Complications of Polydioxanone Foil Use in Nasal Surgery: A Case Series
Authors: Frankel Andrew , Friedman Oren , Wang Leo
Published: April 2018

Polydioxanone (PDS) foil is widely recognized as a septal cartilage replacement during rhinoplasties and is thought to be completely resorbable and biodegradable. Since its United States Food and Drug Administration approval in 2010, PDS foil has drawn significant enthusiasm and many surgeons consider it an ideal implantable biomaterial as reflected in numerous studies highlighting its benefits. However, scant literature exists highlighting relevant complications of PDS plates that may potentially lead to cavalier overuse. This descriptive case series assesses the outcomes of PDS foil usage in three patients seen for septoplasty at two independent institutions over the past 5 years. Our results demonstrate that PDS plate usage can lead to septal cartilage loss and resultant saddle nose deformıty associated with prolonged postoperative edema and inflammation. To our knowledge, this is the largest case series of this reported phenomenon.
Physiologie der Muskel- und Skelettentwicklung
Authors: Semler O. , Hoyer-Kuhn H.-K. , Rehberg M. , Schönau E. , Stark C.
Published: April 2018

Mechanische Kräfte sind essenziell, um die Funktionen von Geweben, wie dem Knochen, aufrechtzuerhalten. Die Wichtigkeit der Muskulatur und deren einwirkende Kräfte auf den Knochen für die Skelettentwicklung sind seit langem bekannt. Das Konzept der funktionellen Muskel-Knochen-Einheit empfiehlt die konsequente Überprüfung der Muskulatur, um primäre von sekundären Skeletterkrankungen zu unterscheiden. Beide haben ein erhöhtes Frakturrisiko gemeinsam, welches es gilt, durch rehabilitative Maßnahmen zu minimieren. Effektive Rehabilitationskonzepte mit Schwerpunkt der Mobilität sollten die Zusammenhänge der Inaktivität und neuromuskulären Kommunikation berücksichtigen. Das multimodale Rehabilitationsprogramm „Auf die Beine“ für Kinder und Jugendliche mit Bewegungsstörungen ist translational aus Modellen zur funktionellen Muskel-Knochen-Einheit entstanden und es konnte eine positive Entwicklung der Mobilität bei Kindern und Jugendlichen mit Störungen der Mobilität nach Teilnahme festgestellt werden.
Hemoptysis and Endometriosis: An Unusual Association — Case Report and Review of the Literature
Authors: Leonardo-Pinto Joao Paulo , Benetti-Pinto Cristina Laguna , Quagliato Iuri , Yela Daniela Angerame
Published: April 2018

Thoracic endometriosis syndrome is a rare condition that includes four entities: catamenial pneumothorax, catamenial hemothorax, catamenial hemoptysis and lung nodules. We describe the case of a 23-year-old woman with complaints of hemoptysis during menstrual period in the two years prior to the appointment. Initially, a treatment for tuberculosis was established with no success. Further investigation showed a 4 mm nodule in the right lung, and the transvaginal ultrasonography indicated the presence of deep endometriosis. Considering the occurrence of symptoms only during menses, an empirical therapy was instituted with remission of the complaints.
Predictors of Bleeding in Patients with Symptomatic Peripheral Artery Disease: A Cohort Study Using The Health Improvement Network in the United Kingdom
Authors: Cea Soriano Lucía , Fowkes F. Gerry , Allum Alaster , Johansson Saga , García Rodriguez Luis
Published: April 2018

The purpose of this analysis was to assess potential predictors of intra-cranial bleeding (ICB) and gastrointestinal bleeding (GIB) in patients with symptomatic peripheral artery disease (PAD) in UK primary care. Patients with symptomatic PAD diagnosed from 2000 to 2010 were identified from The Health Improvement Network (THIN; N = 28,484). A nested case–control analysis, adjusted for potential confounders, was performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for potential predictors of ICB or GIB. For GIB, follow-up was restricted to Hospital Episode Statistics-linked THIN practices. Median follow-up was 6 years. For ICB (153 cases), the OR (95% CI) was 3.85 (1.33–11.13) for previous ICB, 0.90 (0.61–1.34) for treated hypertension, 1.59 (0.65–3.87) for untreated hypertension and 1.38 (0.80–2.36) for current smoking. ORs for ICB were 0.78 (0.50–1.21), 0.40 (0.09–1.82) and 1.27 (0.47–3.47) with use of acetylsalicylic acid (ASA), clopidogrel and warfarin monotherapy, respectively, compared with non-use of such therapy. For GIB (506 cases), the OR was 1.40 (1.05–1.86) for peptic ulcer disease, 3.20 (1.81–5.64) for dual anti-platelet therapy use, 1.96 (1.46–2.64) for non-steroidal anti-inflammatory drug (NSAID) use and 1.01 (0.80–1.28) for proton pump inhibitor use. ORs for GIB were 1.78 (1.39–2.30), 2.03 (1.05–3.93) and 1.25 (0.72–2.16) with ASA, clopidogrel and warfarin monotherapy, respectively, compared with non-use. Previous ICB was a risk factor for ICB. Use of anti-platelet therapy or NSAIDs increased GIB risk. Identifying bleeding predictors could help optimize treatment strategies for patients with PAD.
Mangelernährung bei geriatrischen Traumapatienten
Authors: Bliemel C. , Aigner R. , Rolfes C. , Ruchholtz S. , Buecking B. , Eschbach D.
Published: April 2018

Die Inzidenz von Mangelernährung geriatrischer Patienten wird im Allgemeinen mit über 50 % angegeben. Mangelernährung bei geriatrischen Traumapatienten rangiert im Kollektiv der proximalen Femurfrakturen zwischen 30 und 50 %. Insgesamt erscheinen sowohl die angegebenen Häufigkeiten als auch die angewandten Messinstrumente inhomogen. Malnutrition führt zu einer Verschlechterung der Wundheilung, einer längeren postoperativen Immobilität, einem verlängerten Krankenhausaufenthalt sowie zu einer Steigerung der Mortalität. Unter Hinzuziehung bestehender Leitlinien erreichen das Mini Nutritional Assessment (MNA) sowie das Nutritional Risk Screening (NRS) eine ausreichende prädiktive Validität in diesem geriatrischen Patientengut, um ein Screening auf Mangelernährung durchzuführen. Bezüglich möglicher therapeutischer Interventionen ist die Studienlage limitiert: Vorhandene Studien zeigen oft eine geringe Patientenzahl und demente Patienten, die besonders häufig mangelernährt sind, wurden häufig ausgeschlossen. Eine Leitlinie explizit für dieses spezielle Patientengut existiert aktuell nicht. Ein suffizientes Screening des Ernährungszustandes sowie Daten zur Durchführbarkeit und Effizienz einer kurzfristigen perioperativen Nahrungsergänzung könnten einen wichtigen Beitrag zur Stabilisierung dieser oft multimorbiden und fragilen Patienten leisten.
Surfactant effects on interfacial flow and thermal transport processes during phase change in film boiling
Authors: Premnath Kannan N. , Hajabdollahi Farzaneh , Welch Samuel W. J.
Published: April 2018

The presence of surfactants in two-phase flows results in the transport and adsorption of surfactants to the interface, and the resulting local interfacial concentration significantly influences the surface tension between the liquid and vapor phases in a fluid undergoing phase change. This computational study is aimed at understanding and elucidating the mechanisms of enhanced flows and thermal transport processes in film boiling due to the addition of surfactants. A change in surface tension results in a change in the critical Rayleigh-Taylor wavelength leading to different bubble release patterns and a change in the overall heat transfer rates. Due to the presence of surfactants, an additional transport mechanism of the Marangoni convection arises from the resulting tangential gradients in the surfactant concentration along the phase interface. Our computational approach to study such phenomena consists of representing the interfacial motion by means of the coupled level set-volume-of-fluid method, the fluid motion via the classical marker-and-cell approach, as well as representations for the bulk transport of energy and surfactants, in conjunction with a phase change model and an interfacial surfactant model. Using such an approach, we perform numerical simulations of surfactant-laden single mode as well as multiple mode film boiling and study the effect of surfactants on the transport processes in film boiling, including bubble release patterns, vapor generation rates, and heat transfer rates at different surfactant concentrations. The details of the underlying mechanisms will be investigated and interpreted.
The development of high-voltage repetitive low-jitter corona stabilized triggered switch
Authors: Geng Jiuyuan , Yang Jianhua , Cheng Xinbing , Yang Xiao , Chen Rong
Published: April 2018

The high-power switch plays an important part in a pulse power system. With the trend of pulse power technology toward modularization, miniaturization, and accuracy control, higher requirements on electrical trigger and jitter of the switch have been put forward. A high-power low-jitter corona-stabilized triggered switch (CSTS) is designed in this paper. This kind of CSTS is based on corona stabilized mechanism, and it can be used as a main switch of an intense electron-beam accelerator (IEBA). Its main feature was the use of an annular trigger electrode instead of a traditional needle-like trigger electrode, taking main and side trigger rings to fix the discharging channels and using SF6/N2 gas mixture as its operation gas. In this paper, the strength of the local field enhancement was changed by a trigger electrode protrusion length Dp. The differences of self-breakdown voltage and its stability, delay time jitter, trigger requirements, and operation range of the switch were compared. Then the effect of different SF6/N2 mixture ratio on switch performance was explored. The experimental results show that when the SF6 is 15% with the pressure of 0.2 MPa, the hold-off voltage of the switch is 551 kV, the operating range is 46.4%–93.5% of the self-breakdown voltage, the jitter is 0.57 ns, and the minimum trigger voltage requirement is 55.8% of the peak. At present, the CSTS has been successfully applied to an IEBA for long time operation.
Front tracking velocimetry in advection-reaction-diffusion systems
Authors: Nevins Thomas D. , Kelley Douglas H.
Published: April 2018

In advection-reaction-diffusion systems, the spreading of a reactive scalar can be significantly influenced by the flow field in which it grows. In systems with sharp boundaries between reacted and unreacted regions, motion of the reaction fronts that lie at those boundaries can quantify spreading. Here, we present an algorithm for measuring the velocity of reaction fronts in the presence of flow, expanding previous work on tracking reaction fronts without flow. The algorithm provides localized measurements of front speed and can distinguish its two components: one from chemical dynamics and another from the underlying flow. We validate that the algorithm returns the expected front velocity components in two simulations and then show that in complex experimental flows, the measured front velocity maps fronts from one time step to the next self-consistently. Finally, we observe a variation of the chemical speed with flow speed in a variety of experiments with different time scales and length scales.
High-performance GaAs/AlAs superlattice electronic devices in oscillators at frequencies 100–320 GHz
Authors: Eisele Heribert , Li Lianhe , Linfield Edmund H.
Published: April 2018

Negative differential resistance devices were fabricated from two epitaxial wafers with very similar GaAs/AlAs superlattices and evaluated in resonant-cap full-height waveguide cavities. These devices yielded output powers in the fundamental mode between 105 GHz and 175 GHz, with 14 mW generated at 127.1 GHz and 9.2 mW at 133.2 GHz. The output power of 4.2 mW recorded at 145.3 GHz constitutes a 50-fold improvement over previous results in the fundamental mode. The highest confirmed fundamental-mode oscillation frequency was 175.1 GHz. In a second-harmonic mode, the best devices yielded 0.92 mW at 249.6 GHz, 0.7 mW at 253.4 GHz, 0.61 mW at 272.0 GHz, and 0.54 mW at 280.7 GHz. These powers exceed those extracted previously from higher harmonic modes by orders of magnitude. The power of 0.92 mW constitutes an improvement by 77% around 250 GHz. The second-harmonic frequency of 317.4 GHz is the highest to date for superlattice electronic devices and shows an increase by 25% over previous results.
Microfluidic chip for non-invasive analysis of tumor cells interaction with anti-cancer drug doxorubicin by AFM and Raman spectroscopy
Authors: Zhang Han , Xiao Lifu , Li Qifei , Qi Xiaojun , Zhou Anhong
Published: April 2018

Raman spectroscopy has been playing an increasingly significant role for cell classification. Here, we introduce a novel microfluidic chip for non-invasive Raman cell natural fingerprint collection. Traditional Raman spectroscopy measurement of the cells grown in a Polydimethylsiloxane (PDMS) based microfluidic device suffers from the background noise from the substrate materials of PDMS when intended to apply as an in vitro cell assay. To overcome this disadvantage, the current device is designed with a middle layer of PDMS layer sandwiched by two MgF2 slides which minimize the PDMS background signal in Raman measurement. Three cancer cell lines, including a human lung cancer cell A549, and human breast cancer cell lines MDA-MB-231 and MDA-MB-231/BRMS1, were cultured in this microdevice separately for a period of three days to evaluate the biocompatibility of the microfluidic system. In addition, atomic force microscopy (AFM) was used to measure the Young's modulus and adhesion force of cancer cells at single cell level. The AFM results indicated that our microchannel environment did not seem to alter the cell biomechanical properties. The biochemical responses of cancer cells exposed to anti-cancer drug doxorubicin (DOX) up to 24 h were assessed by Raman spectroscopy. Principal component analysis over the Raman spectra indicated that cancer cells untreated and treated with DOX can be distinguished. This PDMS microfluidic device offers a non-invasive and reusable tool for in vitro Raman measurement of living cells, and can be potentially applied for anti-cancer drug screening.
Perovskite LaBaCo2O5+δ (LBCO) single-crystal thin films for pressure sensing applications
Authors: Ma Y. J. , Xiao J. Y. , Zhang Q. Y. , Ma C. Y. , Jiang X. N. , Wu B. Y. , Zeng X. Y.
Published: April 2018

Perovskite LaBaCo2O5+δ (LBCO) single-crystal films were deposited on (001) MgO substrates by a magnetron sputtering method and processed into Pirani sensors for investigation of pressure measurements. In comparison to the poly-crystal film deposited under the same condition, the single-crystal LBCO films exhibited rather a large temperature coefficient of resistance and a high sensitivity in response to pressure. The LBCO sensors with dimensions of 30 to 200 μm, which are different from resistor-on-dielectric membrane or micro-beam structures, demonstrated to be capable of making response to the pressures ranging from 5 × 10–2 to 105 Pa with a real dynamic range of 3 to 2 × 103 Pa.
Experimental and numerical study of the effects of a wall on the coalescence and collapse of bubble pairs
Authors: Han Rui , Zhang A-Man , Li Shuai , Zong Zhi
Published: April 2018

Two-bubble interaction is the most fundamental problem in multi-bubbles dynamics, which is crucial in many practical applications involving air-gun arrays and underwater explosions. In this paper, we experimentally and numerically investigate coalescence, collapse, and rebound of non-buoyant bubble pairs below a rigid wall. Two oscillating vapor bubbles with similar size are generated simultaneously near a rigid wall in axisymmetric configuration using the underwater electric discharge method, and the physical process is captured by a high-speed camera. Numerical simulations are conducted based on potential flow theory coupled with the boundary integral method. Our numerical results show excellent agreement with the experimental data until the splashing of the jet impact sets in. With different ranges of γbw (the dimensionless distance between the rigid wall and the nearest bubble center), the interaction between the coalesced bubble and the rigid wall is divided into three types, i.e., “weak,” “intermediate,” and “strong.” As γbw decreases, the contact point of the two axial jets migrates toward the wall. In “strong interaction” cases, only an upward jet towards the upper rigid wall forms and a secondary jet with a larger width appears at the base of the first jet. The collapsing coalesced bubble in a toroidal form splits into many smaller bubbles due to the instabilities and presents as bubble clouds during the rebounding phase, which may lead to a weakened pressure wave because the focusing energy associated with the collapsing bubble is disintegrated.
On-top density functionals for the short-range dynamic correlation between electrons of opposite and parallel spin
Authors: Hollett Joshua W. , Pegoretti Nicholas
Published: April 2018

Separate, one-parameter, on-top density functionals are derived for the short-range dynamic correlation between opposite and parallel-spin electrons, in which the electron-electron cusp is represented by an exponential function. The combination of both functionals is referred to as the Opposite-spin exponential-cusp and Fermi-hole correction (OF) functional. The two parameters of the OF functional are set by fitting the ionization energies and electron affinities, of the atoms He to Ar, predicted by ROHF in combination with the OF functional to the experimental values. For ionization energies, the overall performance of ROHF-OF is better than completely renormalized coupled-cluster [CR-CC(2,3)] and better than, or as good as, conventional density functional methods. For electron affinities, the overall performance of ROHF-OF is less impressive. However, for both ionization energies and electron affinities of third row atoms, the mean absolute error of ROHF-OF is only 3 kJ mol−1.
ReaxFF molecular dynamics simulation of intermolecular structure formation in acetic acid-water mixtures at elevated temperatures and pressures
Authors: Sengul Mert Y. , Randall Clive A. , van Duin Adri C. T.
Published: April 2018

The intermolecular structure formation in liquid and supercritical acetic acid-water mixtures was investigated using ReaxFF-based molecular dynamics simulations. The microscopic structures of acetic acid-water mixtures with different acetic acid mole fractions (1.0 ≥ xHAc ≥ 0.2) at ambient and critical conditions were examined. The potential energy surface associated with the dissociation of acetic acid molecules was calculated using a metadynamics procedure to optimize the dissociation energy of ReaxFF potential. At ambient conditions, depending on the acetic acid concentration, either acetic acid clusters or water clusters are dominant in the liquid mixture. When acetic acid is dominant (0.4 ≤ xHAc), cyclic dimers and chain structures between acetic acid molecules are present in the mixture. Both structures disappear at increased water content of the mixture. It was found by simulations that the acetic acid molecules released from these dimer and chain structures tend to stay in a dipole-dipole interaction. These structural changes are in agreement with the experimental results. When switched to critical conditions, the long-range interactions (e.g., second or fourth neighbor) disappear and the water-water and acetic acid-acetic acid structural formations become disordered. The simulated radial distribution function for water-water interactions is in agreement with experimental and computational studies. The first neighbor interactions between acetic acid and water molecules are preserved at relatively lower temperatures of the critical region. As higher temperatures are reached in the critical region, these interactions were observed to weaken. These simulations indicate that ReaxFF molecular dynamics simulations are an appropriate tool for studying supercritical water/organic acid mixtures.
Bright attosecond γ-ray pulses from nonlinear Compton scattering with laser-illuminated compound targets
Authors: Zhu Xing-Long , Chen Min , Yu Tong-Pu , Weng Su-Ming , Hu Li-Xiang , McKenna Paul , Sheng Zheng-Ming
Published: April 2018

Attosecond light sources have the potential to open up totally unexplored research avenues in ultrafast science. However, the photon energies achievable using existing generation schemes are limited to the keV range. Here, we propose and numerically demonstrate an all-optical mechanism for the generation of bright MeV attosecond γ-photon beams with desirable angular momentum. Using a circularly polarized Laguerre-Gaussian laser pulse focused onto a cone-foil target, dense attosecond bunches (≲170 as) of electrons are produced. The electrons interact with the laser pulse which is reflected by a plasma mirror, producing ultra-brilliant (∼1023 photons/s/mm2/mrad2/0.1%BW) multi-MeV (Eγ,max > 30 MeV) isolated attosecond (≲260 as) γ-ray pulse trains. Moreover, the angular momentum is transferred to γ-photon beams via nonlinear Compton scattering of ultra-intense tightly focused laser pulse by energetic electrons. Such a brilliant attosecond γ-photon source would provide the possibilities in attosecond nuclear science.
Microfluidic platform for probing cancer cells migration property under periodic mechanical confinement
Authors: Ma Dongce , Wang Ran , Chen Shuxun , Luo Tao , Chow Yu-Ting , Sun Dong
Published: April 2018

Cancer cell migration and invasion, which are involved in tumour metastasis, are hard to predict and control. Numerous studies have demonstrated that physical cues influence cancer cell migration and affect tumour metastasis. In this study, we proposed the use of a microchannel chip equipped with a number of vertical constrictions to produce periodic compression forces on cells passing through narrow channels. The chip with repeated vertical confinement was applied on adherent MHCC-97L liver cancer cells and suspended OCI-AML leukaemia cells to determine the migration ability of these cancer cells. Given the stimulation of the periodic mechanical confinement on-chip, the migration ability of cancer cells was promoted. Moreover, the migration speed increased as the stimulation was enhanced. Both AFM nanoindentation and optical stretching tests on cancer cells were performed to measure their mechanical property. After confinement stimulation, the cancer cells possessed higher deformability and lower stiffness than non-stimulating cells. The confinement stimulation altered the cell cytoskeleton, which governs the migration speed. This phenomenon was determined through gene expression analysis. The proposed on-chip cell migration assays will help characterise the migration property of cancer cells and benefit the development of new therapeutic strategies for metastasis.
Imaging mycobacterial growth and division with a fluorogenic probe
Authors: Hodges Heather L. , Brown Robert A. , Crooks John A. , Weibel Douglas B. , Kiessling Laura L.
Published: April 2018

Significance

Mycobacteria, including the notorious pathogen
Mycobacterium tuberculosis
, possess a mycolic acid membrane that is a barrier to antibiotics. Although key enzymes that generate this structure are known, a full understanding of cell envelope assembly is lacking. We synthesized a fluorogenic analog of trehalose monomycolate, the building block used by mycolyltransferase enzymes to construct the mycolic acid membrane. When this analog, termed QTF, is processed in cells by mycolyltransferases, fluorescence is generated. Thus, mycolic acid membrane biosynthesis can be monitored in real time over several generations. Although mycolyltransferases are the most abundantly secreted proteins, we found that mycolyltransferase activity is localized. Finally, we show QTF has diagnostic features in that its processing by mycolyltransferases allows it to selectively detect mycobacteria.
KIF15 nanomechanics and kinesin inhibitors, with implications for cancer chemotherapeutics
Authors: Milic Bojan , Chakraborty Anirban , Han Kyuho , Bassik Michael C. , Block Steven M.
Published: April 2018

Significance

Eg5, a mitotic kinesin, has long been an anticancer drug target. However, a different kinesin motor, KIF15, can rescue cell division when Eg5 is incapacitated, leading to chemotherapeutic resistance. We characterized KIF15 motor mechanics at the single-molecule level and studied the effects of combinations of small-molecule inhibitors of KIF15 and Eg5 on admixtures of motors in a motility assay, as well as on cancer cell proliferation. Taken together, our results point the way toward a strategy of combination drug therapy targeting both Eg5 and KIF15 as a means of overcoming KIF15-mediated cancer resistance. This work highlights the importance of understanding the molecular physiology of different kinesins and of exploring inhibitors that target additional mitotic kinesins.
Ratcheting ambition to limit warming to 1.5 °C – trade-offs between emission reductions and carbon dioxide removal
Authors: Holz Ceecee , Siegel Lori S , Johnston Eleanor , Jones Andrew P , Sterman John
Published: April 2018

Mitigation scenarios to limit global warming to 1.5 °C or less in 2100 often rely on large amounts of carbon dioxide removal (CDR), which carry significant potential social, environmental, political and economic risks. A precautionary approach to scenario creation is therefore indicated. This letter presents the results of such a precautionary modelling exercise in which the models C-ROADS and En-ROADS were used to generate a series of 1.5 °C mitigation scenarios that apply increasingly stringent constraints on the scale and type of CDR available. This allows us to explore the trade-offs between near-term stringency of emission reductions and assumptions about future availability of CDR. In particular, we find that regardless of CDR assumptions, near-term ambition increase (‘ratcheting’) is required for any 1.5 °C pathway, making this letter timely for the facilitative, or Talanoa, dialogue to be conducted by the UNFCCC in 2018. By highlighting the difference between net and gross reduction rates, often obscured in scenarios, we find that mid-term gross CO2 emission reduction rates in scenarios with CDR constraints increase to levels without historical precedence. This in turn highlights, in addition to the need to substantially increase CO2 reduction rates, the need to improve emission reductions for non-CO2 greenhouse gases. Further, scenarios in which all or part of the CDR is implemented as non-permanent storage exhibit storage loss emissions, which partly offset CDR, highlighting the importance of differentiating between net and gross CDR in scenarios. We find in some scenarios storage loss trending to similar values as gross CDR, indicating that gross CDR would have to be maintained simply to offset the storage losses of CO2 sequestered earlier, without any additional net climate benefit.