bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser vibrometer condition assessment of cemented materials using wavelet synchro-squeezed transform
Authors: Wiciak Piotr , Cascante Giovanni , Polak Maria Anna
Published: October 2020

Current non-destructive ultrasonic techniques (NDT) are based mostly on wave velocity analysis. While current techniques can identify severe damage, they fail to detect early deterioration. Therefore, the proposed method, based on the propagation of surface waves, takes into account not only changes in wave velocity but also changes in wave attenuation. In practical/field applications, access to a structure is often limited to one side only (i.e. concrete slabs, vacuum building walls). Thus, surface wave analysis is a natural solution. To improve the reliability of wave attenuation measurements, responses of ultrasonic transducers are measured using a high-frequency Doppler laser vibrometer. Firstly, the ultrasonic transducer is characterized using the laser vibrometer. Then, based on the sensitive frequency ranges, response signals measured for the cemented sand specimen are analyzed, and the relative attenuation index based on spectral energy is proposed. The method is further improved using the wavelet synchro-squeezed transform.
Shear tests on GFRP reinforced concrete beams
Authors: Szczech Damian , Kotynia Renata
Published: October 2020

This paper aims to investigate the shear failure mechanisms in beams reinforced with longitudinal and transverse glass fibre reinforced polymer bars. It is a part of comprehensive research on shear in concrete beams reinforced with steel and GFRP bars. The experimental program is composed of six real-scale single-span, simply-supported T-cross section concrete beams. The beams varied mainly with respect to the longitudinal reinforcement ratio (2.91% and 3.69%), bar diameter (25mm and 28mm, respectively) and transverse reinforcement ratio (0.16% and 0,33%). The paper presents test results, cracking patterns, failure modes and an analysis of the influence of variable parameters on the shear behaviour of elements.
Mechanical fracture properties of concrete with lunar aggregate simulant
Authors: Seitl Stanislav , Miarka Petr , Rozsypalová Iva , Pokorná Katka , Keršner Zbyněk , Katzer Jacek , Zarzycki Paweł K.
Published: October 2020

From the volumetric point of view, aggregate is the most important ingredient in any kind of concrete. It is impossible to use raw soil instead of aggregate to produce concrete. There are numerous reasons for not using soil for concrete production on Earth, and we should not use lunar soil for concrete production on the Moon for the same reasons. Nevertheless, almost all developed lunar concrete-like composites, such as sulphur or polymeric concretes, are based on raw lunar soil. In the research programme, cement composite based on lunar aggregate simulant was tested. The mechanical fracture properties of the composite were the key point of interest. It was proven that the tested lunar concrete is characterized by stable and uniform properties. The obtained results were compared with the properties of other ordinary cement composites.
Modification of early strength parameters of concrete by the addition of fly ash and admixture of nano C-S-H for application in 3D printing
Authors: Szostak Bartosz , Golewski Grzegorz L.
Published: October 2020

In the paper, the authors present the results of tests concerning traditional cement mortars with the addition of silica fly ash and the C-S-H nano-admixture. The use of fly ash results in improved plasticity of the mixture. The use of the C-S-H nano-admixture has a positive effect on shortening the setting time and a rapid increase in the strength of mixtures without losing their subsequent properties, which is presented in the research described in the paper. On this basis, the impact of fly ash and the nano-admixture on the selected parameters of the cement paste in the early maturation periods was determined – after 4, 8, 12, 24, 72h and also 7 and 28 days. The following tests were carried out on previously prepared samples: the compressive strength test on a hydraulic press, the test of setting time and the test of cement matrix shrinkage.
Der Blutungsnotfall – Versorgungskonzepte für Patienten mit unbekannter Blutgruppe
Authors: Selleng Kathleen
Published: October 2020

Die Mortalität von Patienten, die mit lebensbedrohlichen Blutungen ins Krankenhaus aufgenommen werden, beträgt bis zu 50%. Für die Verbesserung der Überlebenschancen dieser Patienten ist ein gut etabliertes Hämotherapiekonzept für jedes Krankenhaus unabdingbar. Dies schließt ein, dass die Blutprodukte schnell am Patienten ankommen, d. h. klare Meldewege zwischen Versorgungsort und Blutdepot, dass der Dokumentationsaufwand minimal ist, aber auch dass die Empfehlungen der deutschen Hämotherapie-Richtlinien beachtet werden. In der Praxis eignen sich kleine Blutproduktdepots in Schockraumnähe und eine einfache Anforderungslogistik mit fest zusammengestellter Lieferung von Blutprodukten. Neue Ansätze sind Transportdepots für Rettungshubschrauber und Notarztwagen. Typischerweise werden 0 Rhesus-negative (RhD-negative) Erythrozytenkonzentrate (EKs) für die Notfallversorgung von Patienten mit unbekannter Blutgruppe verwendet, aber häufig stehen diese nicht in ausreichendem Maß zur Verfügung. An der Universitätsmedizin Greifswald werden seit dem Jahr 2000 Rhesus-positive (RhD-positive) EKs für die Transfusion von Patienten mit unbekannter Blutgruppe verwendet, um nicht unnötig RhD-positive Patienten mit 0 RhD-negativen EKs zu transfundieren. Wir konnten zeigen, dass die Verwendung von 0 RhD-positiven EKs keinen Einfluss auf die Überlebenschance der 0 RhD-negativen Patienten hatte und hämolytische Transfusionsreaktionen nicht vermehrt auftraten. Die Anti-D-Immunisierungsrate lag bei 3 – 5% aller Notfallpatienten. Die geforderte frühe Plasmatransfusion und Transfusionsratio FFP : EK von ≥ 1 : 2 kann durch eine Flüssigplasmabank gewährleistet werden. Um die Lagerzeit der aufgetauten Plasmen kurz zu halten, verwenden wir für alle Plasmatransfusionen Plasma aus der Flüssigplasmabank. Krankenhäuser sollten für ihre Gegebenheiten Standards für die Therapie von Blutungsnotfällen im Schockraum und im Rettungsdienst entwickeln.
How Safe Is the Use of Ultrasound in Prenatal Medicine? Facts and Contradictions. Part 1 – Ultrasound-Induced Bioeffects
Authors: Dudwiesus Heiko , Merz Eberhard
Published: October 2020

The “Ordinance on Protection Against the Harmful Effects of Non-Ionizing Radiation in Human Applications” will go into effect at the beginning of 2021 1. § 10 of this ordinance prohibits non-medical fetal ultrasound exposure thereby resulting in uncertainty, particularly among affected patients, with respect to the generally accepted theory regarding the lack of ultrasound side effects. Although not a single study has shown a detrimental effect on fetal or child development following exposure to ultrasound, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety has justified the ban with the purely hypothetical possibility of an unidentified side effect. The first part of the following study shows which ultrasound-induced biophysical effects are known and which dose-dependent threshold values must be taken into consideration. In particular, the study focuses on the well-researched heat effect with some in vivo measurements in humans showing that the actual temperature increase is less than the theoretically calculated values. The planned second part of this study will discuss the non-thermal effects and present the most important epidemiological studies.
Screening, Management and Delivery in Twin Pregnancy
Authors: von Kaisenberg Constantin , Klaritsch Philipp , Ochsenbein-Kölble Nicole , Hodel Markus Eugen , Nothacker Monika , Hecher Kurt
Published: October 2020

The following AWMF guideline (DGGG/AGG & DEGUM responsible) deals with the diagnosis, screening and management of twins as well as the timing and mode of birth.

Twin pregnancies can be classified as dichorionic diamniotic (DC DA), monochorionic diamniotic (MC DA) and monochorionic monoamniotic (MC MA) which are always monochorionic.

Twin pregnancies can be concordant (both twins are affected) or discordant (only one twin is affected) for chromosomal defects, malformations, growth restriction and hemodynamic disorders.

Chorionicity is the prognostically most significant parameter. Monochorial twins have significantly higher risks of intrauterine morbidity and mortality compared to dichorial twins.

In particular, general aspects of twin pregnancies such as dating, determination of chorionicity and amnionicity, the labeling of twin fetuses and the perinatal switch phenomenon are discussed.

Routine monitoring of MC and DC twin pregnancies with ultrasound at 11–13+ 6 weeks of gestation for chromosomal defects, invasive prenatal diagnosis, first-trimester NT or CRL discrepancies, early diagnosis of fetal anatomical defects, and management of twins with abnormalities, including selective fetocide, is described.

Second trimester screening and management for preterm birth, intrauterine selective growth restriction (sFGR), classification of monochorial twins with sFGR, and management of the surviving twin after the death of the co-twin are described.

Complications exclusively affecting MC twins include Twin to Twin Transfusion Syndrome (TTTS) with the important topics screening, prognosis, complications of laser therapy, timing of delivery, risks for brain abnormalities and delayed neurological development, Twin Anemia-Polycythemia Sequence (TAPS) and Twin Reversed Arterial Perfusion (TRAP) Sequence. This also includes MC MA twins as well as conjoined twins.

Finally, the birth mode and time for DC and MC twin pregnancies are described.

The information is summarized in 62 recommendations for action, 4 tables and 8 illustrations with comprehensive background texts.

The guideline is an international guideline adaptation (ISUOG, NICE) as well as a systematic literature search and is up-to-date.
Highly Functionalized Pyrrolylpyridines from 2-(Acylethynyl)-pyrroles
Authors: Trofimov Boris A. , Tomilin Denis N. , Sobenina Lyubov N. , Ushakov Igor A.
Published: October 2020

A novel family of pharmaceutically prospective, densely functionalized (aryl-, hetaryl-, acyl-, and vinyl-substituted) pyrrolylpyridines has been assembled in up to 95% yields via the amination (NH4Cl/K2CO3/DMSO system, 90 °C, 16 h) of 2-(acylethynyl)pyrroles, followed by cyclization (MeOH, reflux, 6 h, up to 90% yield) of the formed intermediate 1-(pyrrol-2-yl)-1-aminoenones with acetylenic ketones (Bohlmann–Rahtz reaction). The intermediate pyrrolyl aminodienones, prospective building blocks for organic synthesis, can be separately synthesized (DMSO, 90 °C, 6 h) in 70–86% yields. A novel facet of this chemistry is stereoselective synthesis of C-vinylated pyridines, (E)-3-[5-acyl-2-aryl-6-(pyrrol-2-yl)pyridin-3-yl]-1-arylprop-2-en-1-ones, by involving the second molecule of acylacetylene into the reaction.
Synthesis, Spectral Characterization and Crystal Structure of Chlororhodibalamin: A Synthesis Platform for Rhodium Analogues of Vitamin B12 and for Rh-Based Antivitamins B12
Authors: Kräutler Bernhard , Widner Florian J. , Kieninger Christoph , Wurst Klaus , Deery Evelyne , Lawrence Andrew D. , Warren Martin J.
Published: October 2020

Chlororhodibalamin (ClRhbl), a rhodium analogue of vitamin B12 (cyanocobalamin), was prepared in 84% yield by metalation of the metal-free B12 ligand hydrogenobalamin using the RhI-complex [Rh(CO)2Cl]2. ClRhbl was identified and characterized by UV/Vis, circular dichroism, high-resolution mass and heteronuclear NMR spectra. The RhIII-corrin ClRhbl features the ‘base-on’ architecture of vitamin B12. X-ray analysis of single crystals of ClRhbl have revealed its detailed 3D-geometry and close structural similarity to the CoIII-analogue chlorocobalamin (ClCbl). ClRhbl is a versatile starting material for the preparation of other rhodibalamins, among them the organometallic derivatives adenosylrhodibalamin and methylrhodibalamin, the Rh analogues of the important coenzyme and cofactor forms of B12, adenosylcobalamin and methylcobalamin.
Synthesis of Catenanes from a BMP32C10-Based Cryptand Tuned by the Linkage Length of Paraquat Salts
Authors: Li Shijun , Yan Feng-Zhi , Shao Yuan-Guang , Zhang Zibin , Shen Yan-Feng , Huang Xue-Chun , Zhang Pei-Ling
Published: October 2020

A series of catenanes have been synthesized through olefin metathesis from a BMP32C10-based cryptand and paraquat guests attached with two terminal alkenes. Distribution of the catenane products can be significantly affected by the linkage length on the paraquat guests. In the presence of BMP32C10-based cryptand, the paraquat salt with a long linkage facilitates intramolecular olefin metathesis to release a [2]catenane as the sole catenation product, while the use of a paraquat salt with a shorter linkage leads to the simultaneous generation of [2]-, [3]-, and [4]-catenanes.
Predicting Anticoagulation Need for Otogenic Intracranial Sinus Thrombosis: A Machine Learning Approach
Authors: Kaufmann Matthew R. , Camilon Philip Ryan , Levi Jessica R. , Devaiah Anand K.
Published: October 2020

Objective The role of anticoagulation (AC) in the management of otogenic cerebral venous sinus thrombosis (OCVST) remains controversial. Our study aims to better define when AC is used in OCVST.

Methods MEDLINE, EMBASE, and The Cochrane Library were searched from inception to February 14, 2019 for English and English-translated articles. References cited in publications meeting search criteria were searched. Titles and abstracts were screened and identified in the literature search, assessing baseline risk of bias on extracted data with the methodological index for nonrandomized studies (MINORS) scale. Random effects meta-regression followed by random forest machine learning analysis across 16 moderator variables between AC and nonanticoagulated (NAC) cohorts was conducted.

Results A total of 92% of treated patients were free of neurologic symptoms at the last follow-up (mean 29.64 months). Four percent of AC and 14% of NAC patients remained symptomatic (mean 18.72 and 47.10 months). 3.5% of AC patients experienced postoperative wound hematomas. AC and NAC recanalization rates were 81% (34/42) and 63% (five-eights), respectively. OCVST was correlated with cholesteatoma and intracranial abscess. Among the analyzed covariates, intracranial abscess was most predictive of AC and cholesteatoma was most predictive of NAC. Comorbid intracranial abscess and cholesteatoma were predictive of AC.

Conclusion The present study is the first to utilize machine learning algorithms in approaching OCVST. Our findings support the therapeutic use of AC in the management of OCVST when complicated by thrombophilia, intracranial abscess, and cholesteatoma. Patients with intracranial abscess and cholesteatoma may benefit from AC and surgery. Patients with cholesteatoma can be managed with NAC and surgery.
The Role of CD68 (+) Histiocytic Macrophages in Nasal Polyp Development
Authors: Bayar Muluk Nuray , Arikan Osman Kürşat , Atasoy Pınar , Kiliç Rahmi , Tuna Yalçinozan Eda
Published: October 2020

Objectives The aim of this study was to investigate the role of CD68 (+) histiocytic macrophages (H-M) in the nasal polyp pathogenesis.

Materials and Methods The study group consisted of 24 adult patients with nasal polyposis. The control group consisted of 11 adult patients without nasal polyps. A total of 36 nasal polyp samples (10-nasal cavity, 10-maxillary sinus, and 16-ethmoid sinus) from the study group and 11 inferior turbinate samples from the control group were analyzed by immunohistochemical staining, with monoclonal antibodies against CD68 (+) H-M.

Results CD68 positivity was significantly higher than the control group in the subepithelial (SE) layer of the ethmoid sinus, and deep layers of nasal cavity, maxillary, and ethmoid sinuses. In SE and deep layers of ethmoid and maxillary sinuses, CD68 positivity was significantly higher than that of the epithelial layer. In the deep layer, histiocytic macrophages tended to gather around eosinophils.

Conclusion The high numbers of CD68 (+) histiocytic macrophages mainly located in deep layer of lamina propria may be responsible for the phagocytosis of eosinophils within the polyp tissue. Therefore, it may be concluded that increased macrophages in nasal polyps do not trigger the growth of nasal polyps. Instead, they may serve to reduce the number of eosinophils in already-developed nasal polyps.
Hormonal Contraceptives and the Risk of Venous Thrombosis
Authors: Khialani Deeksha , Rosendaal Frits , Vlieg Astrid van Hylckama
Published: October 2020

The risk of venous thrombosis (VT) varies according to the type of progestogen that is found in combined oral contraceptives (COCs). When combined with the estrogen component ethinylestradiol (EE), the androgenic progestogens are better able to counteract the EE-induced stimulation of liver proteins and hence are associated with a twofold decreased risk of VT compared with non- or antiandrogenic progestogens, which exert limited counteraction of EE. Because EE is responsible for the increased risk, novel estrogens such as estradiol were developed and seem to have a lower risk of VT than EE. Besides COCs, there are other methods of hormonal contraceptives, such as progestogen-only contraceptives, which do not increase VT risk, except for injectables. Other nonoral contraceptives are combined vaginal rings and patches. There is insufficient evidence regarding the risk of VT associated with these two methods compared with COCs. The increased risk associated with COCs is more pronounced in women with inherited thrombophilia. In these women, the progestogen levonorgestrel seems to be associated with the lowest risk of VT. Currently, there are no studies that have investigated the risk of VT in women who switch COCs. We hypothesize that switching COCs, even when switching from a high- to a low-risk COC, increases the risk of VT. Finally, risk prediction models in women who use COCs are lacking. Since there is a large number of VT cases associated with COC use, it is important to identify women at risk of VT and advise them on alternative contraception methods.
Digitalisierung des Gesundheitswesens: Wir brauchen klare Regeln für die Daten
Authors: Gocke Peter
Published: October 2020

Mit Staunen lässt sich in den letzten Monaten erleben, welche Fortschritte das Thema „Digitalisierung“ in Deutschland gemacht hat – und das branchenübergreifend, nicht nur im Gesundheitswesen.
Uniklinik Düsseldorf: Cyberangriff verursacht Todesfall
Authors: Kucera Martin
Published: October 2020

Ein massiver Ausfall der Klinik-IT hat das Uniklinikum Düsseldorf tagelang schwer beeinträchtigt. Bis Redaktionsschluss versuchten Techniker, das Haus aus dem erzwungenen Notbetrieb zu holen. Ursache war eine Hackerattacke. Die Staatsanwaltschaft ermittelt inzwischen auch wegen fahrlässiger Tötung.
Krankenhausfinanzierung: Ohne neue Strukturen kein Geld
Authors: Doelfs Guntram
Published: October 2020

Spätestens mit der Corona-Pandemie ist die Debatte um eine grundlegende Krankenhausreform und die Zukunft des DRG-Systems wieder voll entbrannt. Jens Spahn ging auf dem Krankenhausgipfel der DKG die Krankenhauslobby frontal an und stellte klar, dass erst einmal über bedarfsgerechte Strukturen geredet werden müsse.
Krankenhausnetzwerke: Effiziente Konfiguration über die Cloud
Authors: Roller Norbert
Published: October 2020

Die Digitalisierung gewinnt im medizinischen Sektor zunehmend an Bedeutung, um ein Höchstmaß an Leistung, Betreuung und Service liefern zu können. Cloud-basierte Netzwerke sind hierbei – insbesondere in der momentanen Situation – der Schlüssel zum Erfolg.
Electron paramagnetic resonance magnetic field sensors for particle accelerators
Authors: Beaumont Anthony , Giloteaux David , Matheoud Alessandro V. , Buzio Marco , Boero Giovanni
Published: October 2020

We report on four electron paramagnetic resonance sensors for dynamic magnetic field measurements at 36 mT, 100 mT, 360 mT, and 710 mT. The sensors are based on grounded co-planar microwave resonators operating at about 1 GHz and 3 GHz, realized using printed circuit board technology, and on single-chip integrated microwave oscillators operating at about 10 GHz and 20 GHz, realized using complementary metal-oxide-semiconductor technology. The sensors are designed to mark precisely the moment when a time-dependent magnetic field attains a specific value. The trigger from the sensor can be used to preset the output of real-time magnetic field measurement systems, called “B-trains,” which are in operation at several large synchrotron installations, including five of the CERN’s particle accelerators. We discuss in detail the performance achieved, in particular, the magnetic field resolution that is in the range of 0.1 nT/Hz1/2–6 nT/Hz1/2. The effects of material anisotropy and temperature are also discussed. Finally, we present a detailed characterization of the sensors with field ramps as fast as 5 T/s and field gradients as strong as 12 T/m.
Permutations uniquely identify states and unknown external forces in non-autonomous dynamical systems
Authors: Hirata Yoshito , Sato Yuzuru , Faranda Davide
Published: October 2020

It has been shown that a permutation can uniquely identify the joint set of an initial condition and a non-autonomous external force realization added to the deterministic system in given time series data. We demonstrate that our results can be applied to time series forecasting as well as the estimation of common external forces. Thus, permutations provide a convenient description for a time series data set generated by non-autonomous dynamical systems.
Measurement of gradient magnetic field from a ferrofluid drop
Authors: Shih Jyun-Chen , Wu Jin-Lin , Chu Hong-Yu
Published: October 2020

We report that the response of the ferrofluid drop in the magnetic field can be described by the concept of a magnetic dipole. The gradient of the magnetic field in space is measured by the proposed model. Ferrofluid material not only exhibits the fluid property like surface tension and element transport but also can be manipulated by the magnetic field. A model is proposed that regards the bulk magnetization of the ferrofluid drop in the magnetic field as a magnetic dipole. The magnetic length coefficient denoting the ratio of the magnetic length of the dipole and the length of the major axis of the deformed drop is found scaling relation and is consistent with experimental results. A function is proposed that represents the responses of the deformation and traveling motion of the drop due to the presence of the magnetic field. The prolate-shaped traveling ferrofluid drops are demonstrated to measure the gradient of the magnetic field in space.
Inverse design of acoustic metamaterials based on machine learning using a Gauss–Bayesian model
Authors: Zheng Bin , Yang Jing , Liang Bin , Cheng Jian-chun
Published: October 2020

Acoustic metamaterials (AMs) have attracted a substantial amount of attention in recent decades where the parameter design plays an important role. However, conventional design methods generally rely on analytical physical models and require a very large number of evaluations of acoustic performance. Here, we propose and experimentally demonstrate an inverse-design method for AMs based on machine learning using a Gauss–Bayesian model. As a result of the cycle of training and prediction and the use of adaptive acquisition functions, this method allows the parameters of AMs to be efficiently designed for specific functionalities without the need for physical models. Considering the significance of low-frequency ventilated sound absorption, we present a design for a typical acoustic metamaterial absorber with multiple structural parameters that facilitate high sound absorption at low frequencies. In the design process, the parameters were adaptively adjusted to improve the sound absorption performance at low frequencies using only 37 evaluations, and this high absorption performance was verified by the agreement of numerical and experimental results. Because of its low cost, high flexibility, and independence from physical models, this method paves the way for tremendous opportunities in the design of various AMs for particular desired functionalities.
Nanoelectromechanical photothermal polarization microscopy with 3 Å localization precision
Authors: Chien Miao-Hsuan , Schmid Silvan
Published: October 2020

Single-molecule microscopy has become an indispensable tool for biochemical analysis. The capability of characterizing distinct properties of individual molecules without averaging has provided us with a different perspective for the existing scientific issues and phenomena. Recently, super-resolution fluorescence microscopy techniques have overcome the optical diffraction limit by the localization of molecule positions. However, the labeling process can potentially modify the intermolecular dynamics. Based on the highly sensitive nanomechanical photothermal microscopy reported previously, we propose optimizations on this label-free microscopy technique toward localization microscopy. A localization precision of 3 Å is achieved with gold nanoparticles, and the detection of polarization-dependent absorption is demonstrated, which opens the door for further improvement with polarization modulation imaging.
Robin fractional problems with symmetric variable growth
Authors: Bahrouni Anouar , Rădulescu Vicenţiu D. , Winkert Patrick
Published: October 2020

In this paper, we study the fractional p(⋅, ⋅)-Laplacian, and we introduce the corresponding nonlocal conormal derivative for this operator. We prove the basic properties of the corresponding function space, and we establish a nonlocal version of the divergence theorem for such operators. In the second part of this paper, see Sec. IV, we prove the existence of weak solutions of corresponding p(⋅, ⋅)-Robin boundary problems with sign-changing potentials by applying variational tools.
Generic properties of dispersion relations for discrete periodic operators
Authors: Do Ngoc , Kuchment Peter , Sottile Frank
Published: October 2020

An old problem in mathematical physics deals with the structure of the dispersion relation of the Schrödinger operator −Δ + V(x) in Rn with periodic potential near the edges of the spectrum, i.e., near extrema of the dispersion relation. A well-known and widely believed conjecture says that generically (with respect to perturbations of the periodic potential), the extrema are attained by a single branch of the dispersion relation, are isolated, and have nondegenerate Hessian (i.e., dispersion relations are graphs of Morse functions). The important notion of effective masses in solid state physics, as well as the Liouville property, Green’s function asymptotics, and so on hinges upon this property. The progress in proving this conjecture has been slow. It is natural to try to look at discrete problems, where the dispersion relation is (in appropriate coordinates) an algebraic, rather than analytic, variety. Moreover, such models are often used for computation in solid state physics (the tight binding model). Alas, counterexamples exist even for Schrödinger operators on simple 2D-periodic two-atomic structures, showing that the genericity fails in some discrete situations. We start with establishing in a very general situation the following natural dichotomy: the non-degeneracy of extrema either fails or holds in the complement of a proper algebraic subset of the parameters. Thus, a random choice of a point in the parameter space gives the correct answer “with probability one.” Noticing that the known counterexample has only two free parameters, one can suspect that this might be too tight for the genericity to hold. We thus consider the maximal Z2-periodic two-atomic nearest-cell interaction graph, which has nine edges per unit cell and the discrete “Laplace–Beltrami” operator on it, which has nine free parameters. We then use methods from computational and combinatorial algebraic geometry to prove the genericity conjecture for this graph. Since the proof is non-trivial and would be much harder for more general structures, we show three different approaches to the genericity, which might be suitable in various situations. It is also proven in this case that adding more parameters indeed cannot destroy the genericity result. This allows us to list all “bad” periodic subgraphs of the one we consider and discover that in all these cases the genericity fails for “trivial” reasons only.
A magnetic damper for low temperature
Authors: Wang Jin Zhen , Bian Xing , Li Qing , Wu Ji Hao
Published: October 2020

A new magnetic damper is developed for the suspension and vibration isolation of precise instruments working in low-temperature and vacuum environments. The damper comprises permanent magnets, a non-magnetic conductor tube, and a spring, and a room-temperature prototype is designed in COMSOL Multiphysics and verified by experiments. A tubular eddy current damper is chosen because it has less leakage flux than the flat type and better usage of magnetic flux, which leads to higher eddy currents. The adjacent magnets arranged in the reverse direction of magnetization can contribute to obtaining a compact damper. COMSOL Multiphysics is proven to be effective software to predict the performance of an eddy current damper compared with the existing experimental and theoretical results. To apply the damper to low-temperature conditions, the selections of non-magnetic tubes and the permanent magnet are thoroughly analyzed. This study offers the applicability of the magnetic damper in the suspension and vibration isolation of precise instruments and provides suggestions for the design of low-temperature and vacuum magnetic dampers.
A distinct method to eliminate the induced voltage in AC loss determination without phase control
Authors: Shen Liuyang , Liu Cong , Zhang Xingyi , Zhou Youhe
Published: October 2020

AC loss is often considered one of the most important design parameters that guide the fabrication of superconducting devices. Thus, the electrometric method to determine AC loss of superconductors is crucial. Usually, the obtained voltage contains the resistive part and the inductive part. If the induced voltage is large, it will make the result very sensitive to the phase error, and hence, a compensating method is usually adopted. However, phase determination was still needed in the previous studies. In this work, we present an approach to precisely eliminate the unknown induced voltage of the sample just by alternating the inductance of the compensating coil. By determining the minimum of the sample voltage, where the induced voltage of the sample is precisely compensated, the AC loss is then able to be calculated without phase control. The principle of the presented method is strictly certified with the mathematic derivation, along with experimental proof. Current and frequency dependent inductance and loss resistance are obtained naturally. The result reveals that the ratio of induced voltage to resistive voltage decreases exponentially with an increase in current. We also found that the resistance of the CC is determined by both applied currents and frequencies. To universally describe these relations, the cycle resistance r is defined by an exponential function, allowing calculating AC loss with different frequencies just through the data of one frequency, which greatly facilitates the testing process. This method is also expected to be utilized in AC loss measurements for superconducting cables and coils.
Method of information entropy for convergence assessment of molecular dynamics simulations
Authors: Talaat Khaled , Cowen Benjamin , Anderoglu Osman
Published: October 2020

The lack of a reliable method to evaluate the convergence of molecular dynamics simulations has contributed to discrepancies in different areas of molecular dynamics. In the present work, the method of information entropy is introduced to molecular dynamics for stationarity assessment. The Shannon information entropy formalism is used to monitor the convergence of the atom motion to a steady state in a continuous spatial domain and is also used to assess the stationarity of calculated multidimensional fields such as the temperature field in a discrete spatial domain. It is demonstrated in this work that monitoring the information entropy of the atom position matrix provides a clear indicator of reaching steady state in radiation damage simulations, non-equilibrium molecular dynamics thermal conductivity computations, and simulations of Poiseuille and Couette flow in nanochannels. A main advantage of the present technique is that it is non-local and relies on fundamental quantities available in all molecular dynamics simulations. Unlike monitoring average temperature, the technique is applicable to simulations that conserve total energy such as reverse non-equilibrium molecular dynamics thermal conductivity computations and to simulations where energy dissipates through a boundary as in radiation damage simulations. The method is applied to simulations of iron using the Tersoff/ZBL splined potential, silicon using the Stillinger–Weber potential, and to Lennard–Jones fluid. Its applicability to both solids and fluids shows that the technique has potential for generalization to other areas in molecular dynamics.
High velocity outflows along the axis of pulsed power driven rod z-pinches
Authors: Yanuka D. , Theocharous S. , Chittenden J. P. , Bland S. N.
Published: October 2020

We report on initial observations of high velocity outflows from the ends of a rod compressed using pulsed power. 1 mm and 2 mm diameter copper rods were placed in a water bath and driven by ∼0.6 MA currents with rise times of ∼700 ns. Laser backlit framing images and streak photography showed an outflow of the material from the ends of each rod, of the initial velocity of up to 7 km/s, which began ∼500 ns after the start of the current pulse and continued throughout the experiment. Ballistics gel was used to help separate low density gas/plasma from any solid/liquid component in the outflow, successfully capturing the material from larger diameter rods (enabling an estimate of its energy) and tracing the path of the material that passed straight through the gel with smaller rods. Experimental results were compared to 1D and 2D MHD simulations performed with the Gorgon code. These suggested that the outflow had two different components, resulting from two different physical processes. Differences in the resistivity between the copper rod and stainless steel anode result in the opening of a small gap between them and ablated stainless steel being projected above the rod, which is captured in framing and streak images. Later in time, a dense copper material, pinched by the magnetic pressure, is launched—explaining the ballistics gel results. The simulations also suggest that the tamped explosion of the rod surface plays a small role in any outflow.
Growth of the modified two-stream instability in the plume of a magnetically shielded Hall thruster
Authors: Mikellides Ioannis G. , Ortega Alejandro Lopez
Published: October 2020

The electrostatic dispersion relation for an unbounded homogeneous plasma in the presence of unmagnetized ions, magnetized electrons, and an applied magnetic field has been solved numerically in the near-plume of a magnetically shielded Hall thruster. The plasma conditions have been obtained by 2D (r-z) multifluid-particle-in-cell simulations. We find growth of the modified two-stream instability in most regions of the domain, with the fastest growth approaching the fluid-limit ωLH/2, radially away from the channel centerline downstream of the front magnetic poles where ωpe/ωce ∼ 1. In this region, the relative drift between magnetized electrons and beam ions perpendicular to the magnetic field is u ≳ 3 uTi, while that between the counterstreaming beam and cathode ions is ≳4 uTi. The latter suggests that the ion–ion cross field lower hybrid instability may also be active here. The presence of these instabilities can lead to anomalous heating of ions enhancing the average energy with which they impact nearby surfaces.
Thermoreflectance techniques and Raman thermometry for thermal property characterization of nanostructures
Authors: Sandell Susanne , Chávez-Ángel Emigdio , El Sachat Alexandros , He Jianying , Sotomayor Torres Clivia M. , Maire Jeremie
Published: October 2020

The widespread use of nanostructures and nanomaterials has opened up a whole new realm of challenges in thermal management, but also leads to possibilities for energy conversion, storage, and generation, in addition to numerous other technological applications. At the microscale and below, standard thermal measurement techniques reach their limits, and several novel methods have been developed to overcome these limitations. Among the most recent, contactless photothermal methods have been widely used and have proved their advantages in terms of versatility, temporal and spatial resolution, and even sensitivity in some situations. Among them, thermoreflectance and Raman thermometry have been used to measure the thermal properties from bulk materials to thin films, multilayers, suspended structures, and nanomaterials. This Tutorial presents the principles of these two techniques and some of their most common implementations. It expands to more advanced systems for spatial mapping and for probing of non-Fourier thermal transport. Finally, this paper concludes with discussing the limitations and perspectives of these techniques and future directions in nanoscale thermometry.
Dynamic behavior of droplets on confined porous substrates: A many-body dissipative particle dynamics study
Authors: Chen Hao , Nie Qichun , Fang Haisheng
Published: October 2020

Droplets wetting and impacting on porous substrates play a critical role in various printing processes and industrial applications. However, due to the lack of effective observation inside the pores, the dynamic behavior of the droplet is rather unclear. Here, we used a numerical method to investigate the dynamic behavior of droplets spreading on confined porous substrates with different surface fractions. The wetting process has been divided into two stages: the inertial stage and the viscous stage. The numerical results show a power-law evolution of the contact diameter with time, and the exponent has a linear relationship with the surface wettability. The scaling laws proved to have no dependence on the porosity. The presence of confined pores causes the spreading slower and makes the droplet reach an equilibrium state more easily. Then, the impacting process was reported by changing the initial velocities of the droplets. It was found that penetration is always observed after spreading. The wetting transition was captured, and the dimensionless maximum spreading was scaled. Finally, the coalescence-induced droplet jumping has been verified on confined porous substrates with a superhydrophobicity, suggesting the potential of porous structures in designing specific droplet behaviors.
Behaviors of supersonic double-parameter jets and their impingement onto molten bath in BOF steelmaking
Authors: Wang Xi , Liu Guangqiang , Liu Kun
Published: October 2020

The dynamic characteristics of supersonic double-parameter jets and their interaction with the molten pool were experimentally studied. The effects of jet inclination angles and gas flow ratios on gas intensity, coalescence characteristics, and dynamic parameter distributions were discussed. The characteristics of the cavity formed by the interaction of the jet and molten pool were revealed. The results show that the jet inclination angle has more influence on the jet coalescence compared with the gas flow rate. However, the gas flow ratio plays a decisive role in the velocity distribution along the jet centerline compared with the jet inclination angle. The velocity peaks of the double-parameter jets were obviously different at fixed axial distances. Compared with other variables, the small-nozzle inclination has a greater impact on the cavity diameter, while the large-nozzle flow ratio has a greater impact on the cavity depth. The depth and width of the cavity formed by the double-parameter jets are more advantageous than that formed by the single-parameter jets. Furthermore, the double-parameter jets were applied to the actual smelting of a 260t converter.
Ultraminiature AlN diaphragm acoustic transducer
Authors: Hake Alison E. , Zhao Chuming , Ping Lichuan , Grosh Karl
Published: October 2020

Piezoelectric acoustic transducers consisting of a circular aluminum nitride and silicon nitride unimorph diaphragm and an encapsulated air-filled back cavity are reported. Analytical and finite element analysis models are used to design the transducer to achieve low minimum detectable pressure (MDP) within chosen size restrictions. A series of transducers with varying radii are fabricated using microelectromechanical systems (MEMS) techniques. Experimental results are reported for a transducer with a 175 μm radius on a 400 × 500 × 500 μm3 die exhibiting structural resonances at 552 kHz in air and 133 kHz in water. The low-frequency (10 Hz–50 kHz) sensitivity is 1.87 μV/Pa (−114.5 dB re 1 V/Pa) in both air and water. The sensor has an MDP of 43.7 mPa/Hz (67 dB SPL) at 100 Hz and 10.9 mPa/Hz (55 dB SPL) at 1 kHz. This work contributes a set of design rules for MEMS piezoelectric diaphragm transducers that focuses on decreasing the MDP of the sensor through size, material properties, and residual stress considerations.
Reduced screening of remote phonon scattering in thin-film transistors caused by gate-electrode/gate-dielectric interlayer
Authors: Ma Y. X. , Tang W. M. , Lai P. T.
Published: October 2020

Pentacene organic thin-film transistors have been fabricated with their NdTaO gate dielectrics annealed at 200 °C, 400 °C, and 800 °C to study the effects of remote phonon scattering caused by the thermal vibration of the gate dielectric on the carrier transport in the conduction channel. Although the sample annealed at 800 °C can achieve the best dielectric quality (reflected by its lowest oxide-charge density, smallest dielectric surface roughness, and largest pentacene grain size), it shows the lowest carrier mobility of 0.44 cm2/V·s as compared to the highest mobility of 1.69 cm2/V·s for the control sample without dielectric annealing. In addition, this mobility degradation increases with increasing annealing temperature in spite of improving dielectric quality. Transmission electron microscopy shows that higher annealing temperature results in the formation of a thicker Si-gate/gate-dielectric interlayer, which increases the separation between the Si-gate plasmons and the gate-dielectric dipoles to weaken the screening effect of the gate electrode on the remote phonon scattering of the high-k gate dielectric, resulting in a lower carrier mobility. Measurements at high temperatures also support the effects of the interlayer.
Structural and optical properties of transparent, tunable bandgap semiconductor: α-(AlxCr1−x)2O3
Authors: Jangir Ravindra , Srihari Velaga , Bhakar Ashok , Kamal C. , Yadav A. K. , Sagdeo P. R. , Kumar Dharmendra , Tripathi Shilpa , Jha S. N. , Ganguli Tapas
Published: October 2020

Detailed structural and optical properties of α-(AlxCr1−x)2O3 (0 ≤ x ≤ 1) synthesized by the solid state reaction method have been investigated. Single phase α-(AlxCr1−x)2O3 with space group R3¯c is obtained for the full composition range of 0 ≤ x ≤ 1. Variations in the lattice parameters a and c have been determined. Lattice parameter c follows Vegard’s law, while the lattice parameter a shows a clear deviation with a bowing parameter of −0.035 Å. This behavior of the lattice parameters of α-(AlxCr1−x)2O3 with x is explained in detail by studying the local structure. Extended x-ray absorption fine structure spectroscopy shows a reduction in the values of Cr–O bond lengths with composition x. Optical absorption measurements of α-(Al1−xCrx)2O3 for 0 ≤ x ≤ 1 show a large bandgap tunability of 1.9 eV (from 3.4 eV to 5.3 eV). The photoemission spectroscopy data and the analysis of partial density of states obtained from first principles electronic structure calculations suggest that the valence band maxima is mainly composed of Cr 3d levels, which hybridize with the O 2p levels. Increased contribution of O 2p partial density of states is observed with Al substitution, which is expected to enhance p-type carrier conduction in the α-(AlxCr1−x)2O3 system as compared to the parent α-Cr2O3 system. Thus, the large bandgap, its tunability in the UV region, and the predicted enhancement of p-type conductivity in the α-(AlxCr1−x)2O3 system make it a potential candidate for application in UV based photo-detectors and transparent electronics.
Ho:YLF amplifier with Ti:Sapphire frontend for pumping mid-infrared optical parametric amplifier
Authors: Murari Krishna , Zhou Fangjie , Yin Yanchun , Wu Yi , Weaver Bruce , Avni Timur , Larsen Esben , Chang Zenghu
Published: October 2020

We present a Ho:YLF Chirped-Pulse Amplification laser for pumping a longwave infrared Optical Parametric Chirped Pulse Amplifier at a 1 kHz repetition rate. By utilizing a Ti:Sapphire laser as a frontend, 5-μJ seed pulses at 2051 nm laser pulse are generated in a Dual-Chirp Optical Parametric Amplifier, which are amplified to 28 mJ pulses with a pulse duration of 5.6 ps. The scheme offers a potential driver for two-color (800 nm and 8 μm) high harmonic generation with an increased keV x-ray photon flux.
Analysis of aerodynamic characteristics of flexible flapping flap with bidirectional fluid–structure interaction
Authors: Qin Jie , Li Lun , Hao Yongping , Xu Jiulong , Bai Fan , Ye Jintao
Published: October 2020

Birds in nature adjust the shape of their wings in time according to the change in wind resistance to achieve the purpose of increasing lift and reducing drag, thereby achieving higher flight efficiency. Aiming at the aerodynamic change caused by the flexible deformation of the flapping wing, an analysis model of the flexible wing is established. The two-way fluid–solid coupling method is used to construct the control equations in an arbitrary Lagrange–Euler coordinate system and analyze the overall aerodynamic changes in the flapping process of the flexible flapping wing and the deformation of the wing surface and skeleton. The simulation results show the following: The larger lift force and forward thrust can be obtained from the flapping of the flexible wing, but the larger flexible deformation will lead to the increase in resistance, which leads to the decline of the overall aerodynamic efficiency. Therefore, the flexible wing structure should be designed to ensure that the wing has a certain degree of flexibility and improve the stiffness of the wing.