bluuebunny/crossref_metadata_2025 huggingface dataset:
Miniaturised UWB antenna with dual‐band rejection of WLAN/WiMAX using slitted EBG structure
Authors: Ghahremani Mehdi , Ghobadi Changiz , Nourinia Javad , Ellis Mubarak Sani , Alizadeh Farzad , Mohammadi Bahman
Published: December 2018

This study presents a new slitted electromagnetic bandgap (EBG) structure to filter undesired wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) bands in the ultra‐wideband (UWB) spectrum. A simple UWB antenna which consists of a microstrip tapered feed line, a circular patch and a defected ground structure is used as a reference antenna. The antenna is then integrated with a slitted EBG structure near the feed line to notch two interfering bands. The created notched bands by the EBG structure can be independently controlled. Owing to structural symmetry of the proposed antenna, the size can be reduced by approximately half to form a miniaturised antenna. The miniaturised antenna has the same full‐size antenna characteristics with little change in the notched bands specifications. Frequency domain measurement results show that the full‐size and miniaturised antennas have a flat transfer function, and a group delay variation of about 0.5 ns in the entire UWB band except for the notched bands.
Start control of an M3 C‐based FFTS
Authors: Zhang Xiaoliang , Wang Xifan , Wang Xiuli , Huang Qihang , Fan Jiajie , Zhou Qian
Published: December 2018

The fractional frequency transmission system (FFTS) can multiply increase transmission capacity by using a lower frequency to reduce the reactance of the AC transmission system. The modular multi‐level matric converter (M3 C) as the new generation of the AC/AC converter is the critical equipment of FFTS. The self‐start control strategy for M3 C‐based FFTS is proposed and the whole start‐up procedure is divided into the uncontrollable stage and controllable stage. The model of the equivalent circuit in an uncontrollable stage is built and the mathematical relation between the maximum charging current and the current‐limit resistor is obtained. Finally, a digital simulation system of M3 C‐based FFTS is established, and the effectiveness of the proposed control strategies is verified by simulation results.
A coordinating harmonic suppression strategy of a DC microgrid
Authors: Xu Hailiang , Feng Yunpeng , Xu Jianwei , Zhang Yufeng , Wang Shinan
Published: December 2018

Here, a coordinating harmonic suppression strategy of a DC microgrid was proposed. The harmonics introduced from the connected grid and those generated by local non‐linear loads were both considered and evaluated. Then, a coordinating harmonic suppression strategy was presented for two targets. One is to suppress the voltage pulsating in the DC bus capacitor, which aims to mitigate the adverse impact of the grid voltage harmonics. The other is to obtain sinusoidal output voltage waveforms, that is, to improve the power quality of the microgrid system by properly eliminating the harmonics introduced by the non‐linear loads. Simulation studies indicated that the proposed coordinating control can enhance the system stability and ameliorate the power quality of the load side inverters as well.
The electromagnetic effect study of GIS enclosure under high‐frequency electromagnetic pulse
Authors: Chen Shu , Guo Jie , Hu Chengbo , Tao Fengbo , Xie Tianxi , Xu Yang , Jia Jun
Published: December 2018

In gas insulated switchgear (GIS) substation, due to the operation of disconnect switch and circuit breaker, as well as short‐circuit fault, SF6 will break down very rapidly. The superposition of refraction and reflection of high‐frequency travelling waves will cause the very fast transient electromagnetic pulse (EMP). High‐frequency EMP propagating along GIS core wire will couple to GIS enclosure which forms transient enclosure voltage (TEV). Through the study of new GIS enclosure coupling model which can be verified by site test and frequency effect on the enclosure coupling under high‐frequency EMP, results indicate the generation of TEV is closely related to GIS structures and the electromagnetic wave propagation characteristics on its core wire and enclosure. Electromagnetic coupling model must consider the entire propagating and coupling process of EMP in GIS. Paper also shows that TEV is mainly formed by high frequency >0.1 MHz EMP coupling and the difference on coupling extent when frequency is >1 MHz is small.
Effect of a floating conductor on the breakdown performance of a rod–plane air gap
Authors: Yang Guanghua , Wang Shenghui , Chen Weijiang , Lv Fangcheng , Han Bing , Wang Xiaoyu
Published: December 2018

Floating conductor has an effect on the process of air gap discharge, a laboratory experiment has been designed to analyse in detail the development of such discharge in a rod–plane air gap, submitted to an impulse voltage. High‐speed optical observation technology, discharge current measurement technology, and the method for the synchronisation of the above technologies were used in experiments. Experiments obtained the key physical parameters accurately and the authors give a detailed description of the observed phenomena. The coupling mechanism between the positive and the negative discharges have been studied according to the temporal evolution of the floating potential of the conductor. Based on it, a physical model including the process of the first corona initiation and the streamer development, leader inception, the streamer‐leader system propagation, and final jump is proposed. These results will be used for the development and validation of the model of discharge process to obtain numerical simulations of the rod–plane air gap discharge with a floating conductor.
Comparison of boost and LLC converter and active clamp isolated full‐bridge boost converter for photovoltaic DC system
Authors: Liu Jiye , Zheng Zedong , Wang Kui , Li Yong Dong
Published: December 2018

DC collection network offers an attractive alternative to AC network for photovoltaic, as it avoids the charging current issues and reduces the size and weight. Variable voltage gain DC/DC converters play an important role in DC collection network. Two topologies suitable for photovoltaic DC collection are studied. Boost and LLC converter and active clamp isolated full‐bridge boost converter are two converters with high and variable voltage conversion ratio suitable for the photovoltaic system. This work investigates the two converters comprehensively. The topologies are analysed so as to summarise and compare the characteristic of the converters. Soft switching condition is compared to help extend the zero voltage switching range. Voltage and current stress of the two converters are calculated. Loss comparison is made with the theoretical analysis. Advantages and disadvantages are summarised to get a deep insight into their application field.
Examination on the parameter stability region of the VSC control system in VSC‐HVDCtransmission systems
Authors: Xu Long , Su Guoyun , Du Wenjuan , Chen Chen , Ren Bixing , Wang Haifeng
Published: December 2018

Nowadays, the voltage source converter (VSC)‐based high‐voltage direct current (HVDC) transmission technology is widely adopted for the integration of renewable power generations. However, the grid‐connected VSC systems may also cause power system instability issues. This study focuses on the parameter stability region of VSC control system in VSC‐HVDC transmission systems. The small‐signal linearised model of the whole power system is firstly established and on the basis of which the modal analysis method is applied to obtain the parameter stability region of VSC control system. The results show that the region is mainly affected by both the selection of the initial operating point of VSC and the dynamic interaction between the AC system and the VSC. From these two perspectives, the parameter stability regions of the VSC control system under different operating conditions are investigated. Meanwhile, it is found in the study that when modal coupling occurs between the oscillation modes corresponding to AC system and VSC, the parameter stability regions of the VSC control system obtained in the previous analysis will be deteriorated. Consequently, in terms of stability region, an evaluated method for VSC control system is proposed and validated through case study.
Control of electric spring for frequency regulation
Authors: Yuan Chang , Tong Ming , Feng Jiayao , Zhou Ruibing
Published: December 2018

The authors propose a novel control of electric spring for frequency stabilisation. Frequency stability is an important part of power grid stability. At present, utilising energy storage devices, such as batteries, to stabilise frequency fluctuation in the power grid is a hot topic. However, the high cost of energy storage devices becomes a bottleneck in their applications. Electric spring in series with the non‐critical load provides a cost efficient solution for frequency stabilisation. The relationship between the active power of non‐critical load (P) and voltage of critical load (U L) is given by a detailed derivation. Then a novel control is put forward for frequency regulation based on theoretical derivation. A simulation model of single‐phase electric spring in PSCAD/EMTDC is established to validate the theoretical derivation. The detailed simulation results show that electric spring employing the novel control is capable of stabilising frequency fluctuation.
Simulation of the magnetic coupling phenomena in electric vehicle wireless charging
Authors: Zheng Zhong , Song Ruya , Huang Xiaohua , Xu Jinxing , Gao Chao
Published: December 2018

In recent years, wireless charging technology for electric vehicles has aroused widespread concern in the industry. The technology has the advantages of flexibility and convenience, safe operation and low maintenance cost, and is one of the development trends of charging and discharging technology for electric vehicles in the future. The author summarises the current research status from the most crucial aspects of the magnetic coupling structure of wireless charging systems of electric vehicles, which are the transmission coil structure and the resonance compensation network. Finally, the author put forward the urgent problem to be solved at present is the interoperation problem of the magnetic coupling mechanism in different technical routes. Finally, a magnetic field analysis model based on finite element calculation is established, which provides a tool for the interoperability research of magnetic coupling mechanism.
Constrained operation zone of a VSG considering the DC‐side power margin
Authors: Yuan Chang , Yang Dan , Feng Jiayao , Liu Chang
Published: December 2018

Recently, the virtual synchronous generator (VSG) has drawn considerable attention for its function of simulating the electromechanical transient of SG to make converters equip with the characters of inertia, damping, voltage regulating, and frequency regulating. Energy storage systems (ESSs), which are connected to the converter by a DC/DC circuit, are the basis of VSG. The output active power of VSG is restricted by the capacity margin of the grid‐side converter and DC/DC circuit, and the output energy is bounded by the energy margin of ESS, which means that VSG is restrained by treble constraints: DC side power, DC‐side energy, and AC‐side power. A small signal model of VSG is built, and the method of getting the treble constraints is proposed. Through the analysis of the dynamic response characteristics of the VSG, the operating zone of VSG under constraints is confirmed. Simulations in power system computer aided design (PSCAD)/electromagnetic transient including DC (EMTDC) verified the theoretical analysis and the transient characteristics of VSG when the constraints are broken and simulated.
Electrical field distribution of 35 KV Igla under polluted and ice‐covered situation at power frequency
Authors: Jie Guo , Xiaoke Wu , Mengzhen Li , Zexin Zhao , Long Xu
Published: December 2018

Lightning striking on power system may lead to severe accident and huge losses, which is the reason why line arresters are needed. During operation, the electrical field concentration in line arrester may lead to ablation and accelerated aging of insulation materials, and furthermore, cause mal‐operation. A type of line arresters with internal series air gap (IGLA) is chosen by this study, which is distinguished from the previously used metallic oxide arrester, with better characteristic on anti‐flashover when icing, but with worse characteristic on anti‐flashover when polluted. This paper aims at studying the probable variation of power‐frequency electric field of this new kind of IGLA under polluted and icing situation, and making further analysis on the reason why the electric field strength change like this.
Research on overvoltage and minimum air clearance on 1000 kV AC side of converter transformer in ±1100 kV Guquan converter station
Authors: Ying Lou , Zhenqiang Li , Liang Xie , Lei Wan
Published: December 2018

In the hierarchically connected ultra‐high voltage (UHV) DC projects, the minimum air clearance on the 1000 kV AC side of converter transformer directly affects the layout and area of the valve hall. The minimum air clearance is determined by the overvoltage and the flashover characteristics of different electrodes. Since the UHV DC projects are hierarchically connected to the AC power grid, the overvoltage and the electrode flashover characteristics are different from that of general UHV AC projects, necessitating the relevant overvoltage calculation and test studies. The electromagnetic transients software PSCAD is used for modelling of the ±1100 kV Wannan convertor station and the related AC system. The power frequency overvoltage, switching overvoltage, time‐to‐crest value, and coefficient α of phase‐to‐phase overvoltage on the AC side of the 1000 kV converter transformer are calculated. Tests are carried out on air clearances between bundle conductors, tubular buses, and equipment grading rings under switching impulse with 1000 μs long wave‐front. The minimum phase‐to‐earth and phase‐to‐phase air clearances on the 1000 kV AC side of the converter transformer are given.
Effect mechanism of dielectric‐coated electrodes on metal particle lift‐off in SF6 gas
Authors: Zhenyu Zhan , Fangcheng Lü , Hongyu Liu , Zhibing Li , Yan Liu
Published: December 2018

In order to study the influence mechanism of dielectrically coated electrode in SF6 gas under DC electric field on metal particle lift‐off, experimental platform is setup and motion trajectory is recorded by high‐speed camera. The experiment shows that with the increasing of SF6 gas pressures, the lift‐off field of metal particle is increased and the time to reach the high‐voltage electrode shortened. Instantaneous displacement of metal particle is gained by image processing and computational method of charge quantity is raised, analysing of charge quantity shows that the metal particle's charge quantity decreases. Meanwhile, theoretical analysis model of field distribution around metal particle is established, result indicates that there is an enhance of electric field between coating and metal particle and a transform of charge density distribution, which leads to a downward polarisation force for metal particle. The decreasing of the electric charge quantity and the downward polarisation force results in the increasing of the lift‐off field. This article maintains that partial discharge is the charging mechanism of metal particle; the enlargement of SF6 gas pressure brings about the raise of initial electric field of partial discharge, causing the increase of downward polarisation force with higher electric field to lift‐off.
Research on an innovative topology of PFC based on a space nuclear power system
Authors: Jin Yang , Liu Shichao , Dong Baolei , He Xiaobin , Liu Huiying
Published: December 2018

AC/DC power converters have been widely implemented in a variety of power systems. Power factor correction (PFC) is considered as one of the significant technologies in AC/DC converters, which has been researched deeply. A new topology of the boost PFC converter is investigated and related operating principles are analysed. The state space modelling approach is applied to evaluate the performance of the boost converter based on the continuous current mode. To demonstrate the stability of the overall system, an optimal design of a compensation network is carried out through the analysis and modelling of the boost PFC converter. The parameters of the proportional integral controller are determined through the theoretical design and mathematical derivation of the voltage loop and current loop. The control strategy and transient response of the converter are verified in MATLAB SIMULINK, which is able to achieve the zero‐phase and sinusoidal tracking between input current and input voltage.
Dusty spirals triggered by shadows in transition discs
Authors: Cuello N. , Montesinos M. , Stammler S. M. , Louvet F. , Cuadra J.
Published: December 2018

Context. Despite the recent discovery of spiral-shaped features in protoplanetary discs in the near-infrared and millimetre wavelengths, there is still an active discussion to understand how they formed. In fact, the spiral waves observed in discs around young stars can be due to different physical mechanisms: planet/companion torques, gravitational perturbations, or illumination effects.

Aims. We study the spirals formed in the gaseous phase by two diametrically opposed shadows cast at fixed disc locations. The shadows are created by an inclined non-precessing disc inside the cavity, which is assumed to be optically thick. In particular, we analyse the effect of these spirals on the dynamics of the dust particles and discuss their detectability in transition discs.

Methods. We performed gaseous hydrodynamical simulations with shadows, then we computed the dust evolution on top of the gaseous distribution, and finally we produced synthetic ALMA observations of the dust emission based on radiative transfer calculations.

Results. Our main finding is that millimetre- to centimetre-sized dust particles are efficiently trapped inside the shadow-triggered spirals. We also observe that particles of various sizes starting at different stellocentric distances are well mixed inside these pressure maxima. This dynamical effect would favour grain growth and affect the resulting composition of planetesimals in the disc. In addition, our radiative transfer calculations show spiral patterns in the disc at 1.6 μm and 1.3 mm. Due to their faint thermal emission (compared to the bright inner regions of the disc) the spirals cannot be detected with ALMA. However, our synthetic observations prove that shadows are observable as dips in the thermal emission.
Chemical composition of planet building blocks as predicted by stellar population synthesis
Authors: Cabral N. , Lagarde N. , Reylé C. , Guilbert-Lepoutre A. , Robin A. C.
Published: December 2018

Context. Future space missions (TESS, CHEOPS, PLATO, and the JWST) will considerably improve our understanding of the formation and history of planetary systems by providing accurate constraints on planetary radius, mass, and atmospheric composition. Currently, observations show that the presence of planetary companions is closely linked to the metallicity and the chemical abundances of the host stars.

Aims. We aim to build an integrated tool for predicting the planet building blocks (PBBs) composition as a function of the stellar populations to interpret ongoing and future large surveys. The different stellar populations we observe in our Galaxy are characterized by different metallicities and α-element abundances. We here investigate the trends of the expected PBBs composition with the chemical abundance of the host star in different parts of the Galaxy.

Methods. We synthesized stellar populations with the Besançon galaxy model, which includes stellar evolutionary tracks that are computed with the stellar evolution code STAREVOL. We integrated a previously published simple stoichiometric model into this code to determine the expected composition of the PBBs.

Results. We determine the expected PBB composition around FGK stars for the four galactic populations (thin and thick disks, halo, and bulge) within the Milky Way. Our solar neighborhood simulations are in good agreement with the recent results obtained with the HARPS survey for firon, fw, and the heavy element mass fraction fZ. We present evidence of a clear dependence of firon and fw on the initial alpha abundances [α/Fe] of the host star. We find that the different initial [α/Fe] distributions in the different galactic populations lead to a bimodal distribution of PBB composition. Our simulations show an iron valley that separates PBBs with high and low iron mass fractions and a water valley that separates PBBs with high and low water mass fractions.

Conclusions. We linked host star abundances and expected PBB composition in an integrated model of the Galaxy. The trends we derive are an important step for statistical analyses of expected planet properties. In particular, internal structure models may use these results to derive statistical trends of rocky planet properties, constrain habitability, and prepare an interpretation of ongoing and future large-scale surveys of exoplanets.
3D MHD modeling of the expanding remnant of SN 1987A
Authors: Orlando S. , Miceli M. , Petruk O. , Ono M. , Nagataki S. , Aloy M. A. , Mimica P. , Lee S.-H. , Bocchino F. , Peres G. , Guarrasi M.
Published: December 2018

Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field in the dynamics of the expanding remnant of SN 1987A, and the origin and evolution of the radio emission from the remnant, in particular during the interaction of the blast wave with the nebula surrounding the SN.

Methods. We modeled the evolution of SN 1987A from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula using three-dimensional magnetohydrodynamic simulations. The model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-SN ambient magnetic field. We explore the strengths of the pre-SN magnetic field ranging between 1 and 100 μG at the inner edge of the nebula and we assume an average field strength at the stellar surface B0 ≈ 3 kG. From the simulations, we synthesize the thermal X-ray and the non-thermal radio emission and compare the model results with observations.

Results. The presence of an ambient magnetic field with strength in the range considered does not change significantly the overall evolution of the remnant. Nevertheless, the magnetic field reduces the erosion and fragmentation of the dense equatorial ring after the impact of the SN blast wave. As a result, the ring survives the passage of the blast, at least during the time covered by the simulations (40 yr). Our model is able to reproduce the morphology and lightcurves of SN 1987A in both X-ray and radio bands. The model reproduces the observed radio emission if the flux originating from the reverse shock is heavily suppressed. In this case, the radio emission originates mostly from the forward shock traveling through the H II region and this may explain why the radio emission seems to be insensitive to the interaction of the blast with the ring. Possible mechanisms for the suppression of emission from the reverse shock are investigated. We find that synchrotron self-absorption and free–free absorption have negligible effects on the emission during the interaction with the nebula. We suggest that the emission from the reverse shock at radio frequencies might be limited by highly magnetized ejecta.
Non-isothermal crystallization behavior of spinel crystals in FeO-SiO2-TiO2-V2O3-Cr2O3 slag
Authors: Shao Lixiong , Diao Jiang , Zhou Wang , Zhang Tao , Xie Bing
Published: December 2018

The growth behaviour of spinel crystals in vanadium slag with high Cr2O3 content was investigated and clarified by statistical analyses based on the Crystal Size Distribution (CSD) theory. The results indicate that low cooling rate and Cr2O3 content benefit the growth of spinel crystals. The chromium spinel crystals firstly precipitated and then acted as the heterogeneous nuclei of vanadium and titanium spinel crystals. The growth mechanisms of the spinel crystals at the cooling rate of 5 K/min consist two regimes: firstly, nucleation control in the temperature range of 1873 to 1773 K, in which the shapes of CSD curves are asymptotic; secondly, surface and supply control within the temperature range of 1773 to 1473 K, in which the shapes of CSD curves are lognormal. The mean diameter of spinel crystals increases from 3.97 to 52.21 µm with the decrease of temperature from 1873 to 1473 K.
Effects of modification on microstructure and properties of Al-bearing high-boron high-speed steel
Authors: Yaguang Zhang , Fu Hanguang , Jian Lin , Changan Wang , Yongping Lei
Published: December 2018

The microstructure of Al-bearing high-boron high speed steel (AB-HSS) contains a large amount of borocarbides, which makes it have high hardness, superior wear resistance and thermal stability. But the borocarbides are coarser and continuously distribute along the grain boundary which seriously destroys the toughness of AB-HSS. In this paper, the microstructure and properties of AB-HSS were regulated by adding modifiers and quenching and tempering heat-treatment. The modifier was RE-Mg, Ti and N elements. The microstructure and properties of AB-HSS were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), the electron probe microanalysis (EPMA), hardness testing, wear testing, and impact testing. The results show that the borocarbides in as-cast AB-HSS are found in intergranular networks showing different degrees of continuity after adding different types of modifiers. The matrix of as-cast AB-HSS all is composed of ferrite, pearlite and martensite, and the borocarbides all consist of M2(B,C) and M7(C,B)3 after adding different types of modifiers. After high-temperature heat treatment, the borocarbides in the microstructure of RE-Mg modification AB-HSS appear as discontinuous networks showing signs of spheroidization and the distribution of the borocarbides is more uniform. The matrix of RE-Mg modification AB-HSS is martensite and the borocarbides consist of M2(B,C), M7(C,B)3 and M23(C,B)6. The hardness of RE-Mg modification AB-HSS reaches 61.7 HRC, and impact toughness increases by 52%, and has excellent comprehensive mechanical properties.
„Humor macht kein kranckheit“
Authors: Hick Christian
Published: December 2018

Paracelsus was an adventurer in more than one way. We retrace the little that is known about his life and then focus on his adventures in the history of ideas, namely the scientific revolution he brought about for humoral pathology. Following the landmark study of Pagel (1982) we identify two of his conceptions of disease: diseases as fruits and diseases as minerals, discovered by a new science, a “scientia separationis”. Paracelsus did not merely polemize against humoral pathology, but offered a new world view, a new paradigm, so that his endeavor can be characterized with Kuhn (1962) as a scientific revolution.
Gar ned krank is a ned g’sund
Authors: Müller Wilfried , Mann Klaus
Published: December 2018

This article is written in remembrance of Karl Valentin’s 70th anniversary of his death. He was a comedian and song writer suffering from vegetative dystonia and depression lifelong. This hypochondriac developed extreme self observation and had anxiety to get ill permanently. As one year old, his brother died of diphteria and he was close to death himself. After jumping in an ice cold river in Munich as a young man he caught a pneumonia. From that day he had a undefined long lasting lung disease. His performances and pieces of literature in Bavarian dialect are characterized by critical thoughts about the world in general and human vulnerability including his own in a philosophical way. His sarcastic view of the world, which was rarely pleasant for the counterpart still induced admiration of many audiences and was satisfying for Karl Valentin’s egocentrism. He has been the most famous Bavarian comedian during world war II and during the early days of the Republic of Germany.
Prophylaktisches Shuntvenenbanding mit arteriovenöser
Reanastomose
Authors: Krönung Gerhard
Published: December 2018

Prophylaktische Indikationen in der Shuntchirurgie erfordern eine besonders
sorgfältige interdisziplinäre Bewertung, Aufklärung des Patienten und Erfahrung
des Operateurs. Dies gilt besonders, wenn der OP-Erfolg von pathologischen
Substratveränderungen abhängt, die oft erst intraoperativ, also nach der
Indikationsstellung, detailliert beurteilt werden können.
Machʼ mal Pause!
Authors: Jürgens Ute
Published: December 2018

Auch die Pause gehört zur Musik! Dieser Spruch von Stefan Zweig beschreibt das A
und O von guter Leistung. Zur Regeneration brauchen wir eine regelmäßige
Arbeitsunterbrechung. Oft ist zu viel zu tun und wir gönnen uns keine Rast.
Radiological Diagnosis of Soft Tissue Tumors in Adults: MRI Imaging of Selected Entities Delineating Benign and Malignant Tumors
Authors: Lisson Catharina , Lisson Christoph , Beer Meinrad , Schmidt Stefan
Published: December 2018

Objective MRI is the most important and sensitive imaging modality in the differentiation of unclear soft tissue tumors. A systematic approach helps to narrow down the large number of possible differential diagnoses.

Method Our review systematically compares MRI characteristics of the major soft-tissue masses and aims to gain access to these often difficult tumor entities.

Results and conclusion MRI, as the most important modality in the imaging of soft tissue tumors, allows a more detailed classification of the tumor entity and in many cases a differentiation between benign and malignant masses.

Key points: 

Citation Format
Artifacts in 3D Prenatal Sonography
Authors: Miric Tesanic Danka , Merz Eberhard
Published: December 2018

Purpose Artifacts may be part of any 3D sonographic examination during pregnancy and can disturb a routine diagnostic procedure, even simulate fetal malformation. The aim of this study was to classify the artifacts in different types according to their appearance.

Materials and Methods A total of 2349 healthy fetuses examined during the last five years was included in this study. The observed artifacts have been grouped into 6 different types according to their appearance: 1. fetal movement artifacts, 2. shadow artifacts, 3. amputation artifacts caused by the volume box, 4. defects caused by the improper use of the electronic scalpel, 5. artifacts due to an unfavorable threshold adjustment and 6. artifacts due to superimposed objects.

Results Significant artifacts were found in 119 ultrasound examinations: 39 artifacts were caused by fetal movement, 25 by acoustic shadowing, 19 artifacts occurred due to amputation of objects by the volume box and 15 by the improper use of the electronic scalpel. In 12 cases the threshold adjustment was unfavorable and in 9 cases the artifacts were caused by superimposed objects.

Conclusion In 3D ultrasound some artifacts can be avoided by optimizing the size and position of the volume box or by using a different scanning angle. Other artifacts can be minimized using gain and threshold properly and by precise use of the electronic scalpel. In doubtful situations it is recommended to rescan the volume and to use all diagnostic 3D rendering possibilities. Proper recognition of the artifacts can avoid the risk of misdiagnosis.
Total Synthesis of Bryostatin 8 and (–)-Exiguolide: Applications of an Organosilane Strategy
Authors: Zhang Yuebao , Lu Ji , Li Hongze , Sun Xianwei , Gao Lu , Song Zhenlei
Published: December 2018

In this Account, we give an overview of our recent efforts towards the total synthesis of two marine natural products: bryostatin 8 and (–)-exiguolide. The central theme is to highlight the power of the organosilane strategy, which was characterized with our geminal bis(silanes)-based methodologies for constructing the unique exocyclic enoate-substituted pyran rings.

1 Introduction

2 Background of Bryostatins and (–)-Exiguolide

3 Constructing the B-Ring of Bryostatins

4 Total Synthesis of (–)-Exiguolide via an Organosilane Strategy

5 Constructing the C-Ring of Bryostatins

6 Total Synthesis of Bryostatin 8

7 Conclusion
Die Bedeutung von „Social Eating“ für die
Gesundheit
Authors: Zielinski Johanna
Published: December 2018

In der Geschichte der Menschheit spielt das gemeinsame Mahl seit jeher eine
bedeutende Rolle. Im heutigen digitalen Zeitalter erweitern sich die
Möglichkeiten des „gemeinsamen Speisens“. Weltweit gesellen sich Menschen über
Smartphones, Tablets oder PCs an einen gemeinsamen „virtuellen Tisch“. Wie
verändern sich dadurch Wohlbefinden und Gesundheitsstatus der Gesellschaft?
Direct and photon-assisted tunneling in resonant-cavity quantum-well light-emitting transistors
Authors: Qiu Junyi , Wang Curtis Y. , Feng Milton , Holonyak N.
Published: December 2018

Tunneling in a transistor is a critical quantum process toward the next-generation, energy-efficient, high-speed data transfer for both electrical and optical communications. In this work, resonant-cavity quantum-well light-emitting transistors with tunneling collector junctions are designed and fabricated. Three distinctive tunneling mechanisms are clearly identified by the transistor optical output family curves, namely, electron direct tunneling (DT) from collector to base, electron DT from base to collector, and intra-cavity photon-assisted electron tunneling from base to collector. The device operations under both direct and photon-assisted tunneling are explained in detail by the intra-cavity quantum transition of electron-hole pair to photon dynamics. The tunnel junction and the corresponding carrier tunneling injection suggest the possibility of utilizing tunneling to achieve high-speed optoelectronics operations.
Antiferromagnetic MnNi tips for spin-polarized scanning probe microscopy
Authors: Forrester P. R. , Bilgeri T. , Patthey F. , Brune H. , Natterer F. D.
Published: December 2018

Spin-polarized scanning tunneling microscopy (SP-STM) measures magnetoresistance with atomic resolution. While various methods for achieving SP probes have been developed, each is limited with respect to fabrication, performance, and operating conditions. In this study, we present the fabrication and use of SP-STM tips made from commercially available antiferromagnetic Mn88Ni12 foils. The tips are intrinsically SP, which is attractive for exploring magnetic phenomena in the zero field limit. The tip material is relatively ductile, is straightforward to etch, and has a Néel temperature exceeding 300 K. We benchmark the topographic and spectroscopic performance of our tips and demonstrate their spin sensitivity by measuring the two-state switching of holmium single atom magnets on MgO/Ag(100).
Influence of the emission current on a beam-generated plasma
Authors: Levko Dmitry , Gruenwald Johannes
Published: December 2018

The influence of the electron emission current on the beam-generated plasma is analyzed using the self-consistent one-dimensional Particle-in-Cell Monte Carlo collision model. It is established that the emission current can be used to control both the ion current and the ion energy at the anode. It is also found that for the values of the emission current of interest in the present work and the gas pressure of 15 Pa, the plasma density is mainly controlled by the emission current, while only ∼1%–2% of plasma is produced by the plasma electrons being generated in the cathode sheath. The plasma potential, which defines the ion energy at the anode, is controlled by the coupling between the beam and plasma electrons through the excitation of electrostatic waves in the plasma by damping the electron beam.
Energy condition of isothermal magnetoelectric switching of perpendicular exchange bias in Pt/Co/Au/Cr2O3/Pt stacked film
Authors: Nguyen Thi Van Anh , Shiratsuchi Yu , Yonemura Shogo , Shibata Tatsuo , Nakatani Ryoichi
Published: December 2018

Energy condition for isothermal reversible magnetoelectric switching of exchange bias was investigated using Pt/Co/Au/Cr2O3/Pt stacked films with different thicknesses of the antiferromagnetic layer (tAFM). We discussed the effective magnetic anisotropy energy of the antiferromagnetic layer (KAFMeff), the interface exchange coupling energy (JINT), and the offset electric field (E0). The dependence of KAFMeff on tAFM suggested that the magnetic domain wall motion significantly influenced the switching of the electric-field-induced magnetization similar to an ordinal ferromagnet. Below 0.025 mJ/m2, JINT was equal to the exchange anisotropy energy (JK), and above 0.025 mJ/m2, JINT exceeded JK, suggesting that JK is restricted by the magnetic domain wall energy. The dependence of E0 on tAFM revealed that E0 mainly arose from the interfacial uncompensated antiferromagnetic moment. The obtained results suggest that the energetic interpretation of static switching of electric-field-induced magnetization in Cr2O3 was similar to that of the ordinary ferromagnetic materials.
Non-equilibrium strain relaxation noise in the relaxor ferroelectric (PbMg1/3Nb2/3O3)1-x(PbTiO3)x
Authors: Zhang Xinyang , Kennedy Thomas J. , Colla Eugene V. , Weissman M. B. , Viehland D. D.
Published: December 2018

Large low-frequency polarization noise is found in some perovskite relaxor ferroelectrics when they are partially polarized, regardless of whether the polarization is accompanied by an applied electric field. The noise appears both in the ferroelectric and relaxor states, including the nominally ergodic paraelectric state at temperatures above the susceptibility peak. Since it is present whenever the samples have non-zero average piezoelectric coefficients, but not otherwise evident, it appears to be a response to mechanical strain changes. Dependence of the noise on sample thermal history indicates that non-equilibrium strain relaxation is the source, even in the temperature range for which the sample is nominally ergodic. Non-equilibrium noise in the absence of net piezoelectricity is found at somewhat higher frequencies. Related materials lacking a metastable non-equilibrium cubic bulk phase and a symmetry-broken surface layer show very little of the anomalous low-frequency noise. The implications for a non-equilibrium origin of the skin effect are discussed.
Improper integrals as a puzzle for creeping flow around an ellipsoid
Authors: Wang Shiyan , Martin Curtis P. , Kim Sangtae
Published: December 2018

The general ellipsoid immersed in the quadratic ambient velocity field Hijkxjxk with the origin at the ellipsoid center will exhibit an additional Faxén law contribution to the hydrodynamic drag because of the ambient pressure gradient. Here we reexamine the solution of S. Kim and P. Arunachalam [“The general solution for an ellipsoid in low-Reynolds-number flow,” J. Fluid Mech. 178, 535–547 (1987)] for Stokes flow by focusing more carefully on the system of equations and boundary condition on the disturbance velocity field. All of the unknown coefficients (quadrupole moments) in the disturbance velocity were determined by Kim and Arunachalam from a linear system of equations that arise from matching the quadratic terms in the disturbance and ambient fields. Note that when matching the boundary conditions, they interpreted the constant terms in the disturbance velocity field as a complicated but formal expression for the drag on the ellipsoid. Kim and Arunachalam did not explore this further and instead opted for the simpler expression for the drag from a direct application of the Faxén law to the quadratic ambient field. Years later, we provide the resolution of the “mystery” of two seemingly different expressions for the hydrodynamic drag on the ellipsoid by proving their equivalence. One interesting consequence is the emergence of rather formidable integrals that are identically zero. Uniqueness theorems and related properties for Stokes flow provide a guarantee that the two expressions for the drag are equivalent, but we also provide a direct proof via the properties of elliptic integrals and thus provide formal closure to the problem of the ellipsoid in a quadratic ambient field.
21Ne and 131Xe NMR study of electric field gradients and multinuclear NMR study of the composition of a ferroelectric liquid crystal
Authors: Ahola Susanna K. , Ingman Petri , Laatikainen Reino , Sinkkonen Jari , Jokisaari Jukka
Published: December 2018

This study has two goals. First, the electric field gradient (EFG) present in the liquid-crystalline phases of ferroelectric FELIX-R&D is determined using NMR spectroscopy of noble gases 21Ne and 131Xe. The 21Ne and 131Xe NMR spectra were recorded over a temperature range, which covers all the mesophases of FELIX-R&D: nematic N*, smectic A, and smectic C*. The spin quantum number of both 21Ne and 131Xe is 3/2. Their electric quadrupole moment interacts with the EFG at the nuclear site, which in liquid-crystalline phases results in the NMR spectra of the triplet structure, instead of a singlet detectable in the isotropic phase. The total EFG experienced by the noble gas nuclei consists of two contributions; one arises from the quadrupole moments of the liquid crystal molecules (external contribution) and the other one from the deformation of the electron distribution of the atoms (deformational contribution). The total EFGs determined from the 131Xe and 21Ne quadrupole splittings are very similar in the nematic and smectic A phases but differ in the smectic C* phase, being about twice larger in the 21Ne case which stems from the larger deformation of the xenon electron cloud than that of neon. For the first time, EFG was determined also in the smectic C* phase applying noble gas NMR spectroscopy. Second, the structure of molecules which, as a mixture, compose the used ferroelectric liquid crystal, FELIX-R&D, is determined by applying a number of various NMR methods and sophisticated spectral analysis. In this part, NMR spectra were recorded from FELIX-R&D/CDCl3 solution. The NMR spectral analysis was divided into four subsystems with over 13 000 000 nonzero intensity transitions. It appeared that FELIX-R&D is composed of three phenyl pyrimidine derivatives and a chiral dopant with fluorine in the asymmetric carbon atom.
Reconstructing signed networks via Ising dynamics
Authors: Xiang Bing-Bing , Ma Chuang , Chen Han-Shuang , Zhang Hai-Feng
Published: December 2018

Revealing unknown network structure from observed data is a fundamental inverse problem in network science. Current reconstruction approaches were mainly proposed to infer the unsigned networks. However, many social relationships, such as friends and foes, can be represented as signed social networks that contain positive and negative links. To the best of our knowledge, the method of reconstructing signed networks has not yet been developed. To this purpose, we develop a statistical inference approach to fully reconstruct the signed network structure (positive links, negative links, and nonexistent links) based on the Ising dynamics. By the theoretical analysis, we show that our approach can transfer the problem of maximum likelihood estimation into the problem of solving linear systems of equations, where the solution of the linear system of equations uncovers the neighbors and the signs of links of each node. The experimental results on both synthetic and empirical networks validate the reliability and efficiency of our method. Our study moves the first step toward reconstructing signed networks.
Local domain inversion in MgO-doped lithium niobate by pyroelectric field-assisted femtosecond laser lithography
Authors: Imbrock Jörg , Hanafi Haissam , Ayoub Mousa , Denz Cornelia
Published: December 2018

We explore a physical approach to invert ferroelectric domains in the volume of MgO-doped lithium niobate crystals without any external electric field. Permanent defect structures are created by focused infrared femtosecond laser pulses below the material surface along the polar axis followed by a thermal treatment. This procedure leads to an inversion of ferroelectric domains beneath and above the laser-induced filaments up to the surfaces of the crystal. All domain walls are straight and up to 800 μm long. We measure the domain width in dependence on the length of the filaments and the writing energy. The smallest achieved domain width and the domain spacing is 1 μm. We propose a model taking into account the temperature dependence of the pyroelectric field and thermally activated bulk charges to explain the mechanism of domain inversion. Our findings pave the way to all-optical printing of arbitrary ferroelectric domain structures for nonlinear photonic applications.
X-ray radiation hardness and influence on blinking in Si and CdSe quantum dots
Authors: Pevere Federico , von Treskow Carl , Marino Emanuele , Anwar Monib , Bruhn Benjamin , Sychugov Ilya , Linnros Jan
Published: December 2018

We study the effect of X-ray irradiation on the photoluminescence (PL) efficiency and intermittency (blinking) of single Si/SiO2 and CdSe/CdZnS quantum dots (QDs). Our results show that the PL efficiency of Si nanocrystals is not significantly altered up to a cumulative fluence of 1020 photons/m2 (corresponding to ∼300 kGy of absorbed dose in SiO2), while CdSe particles become completely dark already after a 17 times lower fluence. In both types of QDs, the statistical nature of blinking ON- and OFF-times remains unaltered: mono-exponential for Si and power-law for CdSe QDs. However, the evolution of the blinking parameters with absorbed dose depends on the choice of material. On average, both ON- and OFF-time constants do not vary in Si nanocrystals, highlighting their radiation hardness. Instead, the ON-time exponent increases while the OFF-time exponent decreases with the increasing dose for CdSe dots, confirming their efficiency quenching. Ensemble measurements did not show PL spectral changes neither indicated removal of surface ligands in irradiated CdSe dots. Thus, ionization-generated non-radiative centers in the core-shell system modify blinking of CdSe dots and eventually rapidly quench their emission, in contrast to robust Si/SiO2 nanocrystals. Our study is important for the future use of luminescent QDs in harsh environments, such as space, and the engineering of their blinking properties via ionizing radiation.
Enhanced fast ion prompt loss due to resonant magnetic perturbations in KSTAR
Authors: Kim Kimin , Jhang Hogun , Kim Junghee , Rhee T.
Published: December 2018

We report a numerical study for the impact of resonant magnetic perturbation (RMP) on fast ion prompt loss in KSTAR using full orbit following simulation. Experimental observation in KSTAR indicates a sudden increase in RMP-induced fast ion prompt loss when the applied RMP field exceeds a threshold amplitude. Full orbit simulation with 3D perturbed equilibrium computed by the ideal plasma response reproduces the experimentally observed feature of RMP-induced prompt loss of fast ions and the existence of threshold RMP amplitude. Simulation with vacuum fields only shows a small increase in the fast ion loss that is insufficient to explain the observation. We show that the conservation of canonical angular momentum is broken due to the RMP during the fast ion transit, which is consistent with the enhanced fast ion loss above the threshold RMP amplitude. Phase space analysis suggests that trapped and intermediate pitch passing particles modified from initial high pitch passing ones are responsible for the threshold behavior of the fast ion loss in the simulation, while the phase space distribution of lost particles depends on the RMP field configuration.