bluuebunny/crossref_metadata_2025 huggingface dataset:
Experience in using distance technologies under online learning conditions
Authors: Burlakova Irina , Reva Tatyana , Azmetova Rezeda , Golovyashkina Marina , Palanchuk Nadezhda
Published: March 2021

The pandemic situation has revealed some problems in education, which should be solved by educational entities. One of such problems is unreadiness of teachers to organize online classes. More complex aspect is organization of feedback. Some platforms used for online learning demonstrated their incompetence for widescreen education. Not all teachers managed to create comfortable learning digital space for students. This article analyzes the existing situation in vocational training due to transition to distance learning. Some scientists believe that the educational community evidenced revolutionary shift in the pedagogic paradigm. The opinion of other scientists is that today there are no preconditions for changing classic paradigm in pedagogy and only temporary modifications occurring under pandemic conditions should be considered. This article is devoted not only to identification of problems of organization of educational process in distance format but also to proposing solutions to the highlighted problems, verified by the authors, since the circumstances faced by all teachers forced to accelerate transition to digitalization of educational environment. The educational route is now arranged with consideration for digital experience acquired during the pandemic. Due to the experience orientation the article attracts interest not only of university teachers, forced to modify on the go their pedagogical style and to adapt it to the context of current situation, but also of school teachers facing similar problem and locked in forced professional isolation.
Digital educational space in the professional training of music teachers
Authors: Daynova Guzel , Zabbarova Margarita , Karimova Laysan , Levina Irma , Politaeva Tatyana
Published: March 2021

Professional training of music teacher is a versatile and creative process. It includes numerous areas, such as instrumental and vocal training, studying pedagogical technologies for working with children, studying masterpieces of world music art, and, certainly, studying digital resources and technologies. Digital education space is a digital environment integrating opportunities of digital education resources, computer-aided music technologies and tools, which is the basis in training music teacher. The importance of skills of setting as interactive accompaniment and basic user accompaniment in the form of phonogram is also stipulated by the specificity of accompaniment activity of music teacher as one of the major constituents of professional readiness. Imagination of music teacher as a concertmaster (accompanist of children singing) exerts the influence on whether he would be able by means of expressive playing and keyboard technique to underline and to support the temper of children singing, to present clearly and to reproduce instrument features by piano. That is, a music teacher should be aware of organology, know features of instrument sounding and peculiarities of various instruments. This is sufficiently aided by sequencer software with embedded banks of virtual tunes on synthesizer. In digital education space, video is presented as teaching aid for transfer of learning information, that is, it is considered as video aid, video device used for organization of education. Under existing conditions of distance learning, the interaction between teacher–choirmaster, teacher–vocalist, concertmaster, and students is supported by information and communication technologies. Therefore, mastering means and resources of digital education space is aimed at improved of professional training of future music teacher being the basis of formation of personal capabilities and skills of student.
Online learning technologies as a modern direction of learning in communities
Authors: Klevetova Tatyana , Komissarova Svetlana , Popov Konstantin
Published: March 2021

This article discusses the implementation of technologies of online learning in the mode of massive open online courses, namely, online classes, which are considered as a platform for distance learning and interactive communication between students and teacher. These technologies allow to provide the choice of content, rate, forms of work for students, to increase level of individualization and personification of education, to facilitate learning irrespective of place and time of being, to decrease subjectiveness of evaluation of learning results, to make the learning process more accessible. Theoretical foundations of connectivism are considered as a learning theory implementing the learning process on the basis of online information technologies. This approach changes the role of the teacher, who, acting as a tutor, regulates the pace and volume of students’ work, organizes the exchange of information, thereby creating a community. This article determines the reasons and features of creation of communities of teachers and students during studying in massive open online course. In the frames of this study, network community is considered as a group of students and teachers participating in interactive communication by means of network tools, social networks and messengers. This communication format allows to solve the problems of formation not only of subject but also of meta-subject results of learning, namely, communicative properties of students. The features of construction of communicative activity in these communities are exemplified by the course titled Preparing students for USE in mathematics (profile level), implemented in Volgograd State Socio-Pedagogical University on Miroznai platform. Examples of classes are discussed, each being devoted to solution to one of the task types presented in ESU in mathematics of profile level. Analysis of execution of tests proposed in the course demonstrates that the results of the considered students are somewhat higher than those of students studying in isolation.
Potential of the higher mathematics course in digital education
Authors: Kondrashova Zoya , Solokhin Nikolay
Published: March 2021

Rapid changes taking place at present in the society determine the vector of education development, form requirements to an educated person. The connectivism theory, disclosing the features of education environment under conditions of education digitization, allows to outline the learning strategy in individual subjects. The connectivism education is a complex process including plunging into information environment, maximum use of accumulated knowledge, skills to determine timeliness of the acquired knowledge and its relevance under modern conditions, various trends of communication among participants in learning, ability to detect links among various areas of knowledge, theories, concepts. Objective of the research is to substantiate opportunities of application of connectivism education environment during studying mathematics in higher school, to disclose potential of the higher mathematics course and to confirm experimentally the efficiency of the proposed learning strategy. Methods used in the research were as follows: analysis, statistic methods, generalization, systematization, the method of rising from the abstract to the concrete upon consideration of functionality of digital products, system approach, experimental verification of research results. Results and novelty of the research implied the following: substantiation and development of principles of connectivism learning theory, development of the strategy for construction and implementation of educational programs of higher mathematics course, experimental verification of the dependence between the level of mastering the higher mathematics course and the level of use of digital technologies. The use of the connectivism learning theory allowed to outline the approaches to expansion of content of the higher mathematics course. The main features of the presented course are plunging of students into information environment by means of assignments aimed at maximum use of programs for symbolic mathematics. Studying of certain sections of the higher mathematics course, in particular, analytic geometry and linear algebra, is exemplified based on the developed learning strategy.
Clinical Analysis of Primary Nephrotic Syndrome Complicated by
Plastic Bronchitis in Children
Authors: Jia Shi-lei , Ni Fen-fen , Ma Yi-jiao , Wu Yu-hui , Ma Wei-ke , gao Xiao-jie
Published: March 2021

Objective To summarize the clinical features of primary nephrotic
syndrome (PNS) complicated by plastic bronchitis (PB) in children to provide
guidance for treatment.

Methods We conducted a retrospective review of the clinical data of
25 children hospitalized with NS complicated by PB in our Hospital between
10/2016 and 03/2019, and summarized the clinical
manifestations, imaging and fiberoptic bronchoscopy (FOB) examinations,
treatment course and outcome of them.

Results 1). The 25 children, with a nephrotic syndrome (NS) course of
one to 36 months, were all diagnosed with PB after FOB, among which 8 cases
(32%) had respiratory failure and required ventilatory support. All
of them started with respiratory symptoms such as fever and cough, and then
suffered from dyspnea and progressive aggravation after 1–3 day(s)
of onset, with rapid occurrence of bidirectional dyspnea and even
respiratory failure in severe cases. 2). Laboratory test for pathogens:
influenza A virus H1N1 (11 cases), influenza B virus (9 cases), adenovirus
(3 cases) and mycoplasma pneumoniae (2 cases). There was no statistically
significant difference (P>0.05) between children with common NS
complicated by influenza virus (IV) infection (not accompanied by dyspnea)
and those with kidney disease who developed PB in the white blood cell
count, lymphocyte count, the inflammatory biomarkers C-reactive protein
(CRP), procalcitonin (PCT) and humoral immunity (IgG level), yet the total
IgG level was found significantly higher and the blood albumin level lower
in the latter (P<0.05). 3). The 25 children were all examined with
the FOB and treated with lavage, 15 of which had typical bronchial tree-like
casts and 10 broken and stringy casts. Based on histopathological
classification, all children were of Type I. 4). Twenty children
(80%) with influenza were administered the antiviral drug
Oseltamivir, 20 (80%) were treated with antibiotics, oral hormones
were replaced with the same dosage of intravenous Methylprednisolone for 5
cases (20%), and 20 (80%) were intravenously administered
gamma globulins (400–500 mg/kg x 3 days). These children
showed a remarkable improvement after treatment and there were no
deaths.

Conclusion NS children are at high risk of influenza virus infection.
Children with a severe case of NS are more susceptible to PB. If symptoms
like shortness of breath, wheezing and progressive bidirectional dyspnea
occur, FOB examination and lavage treatment should be performed as early as
possible. Hyper-IgE-emia and hypoproteinemia may be the high risk factors
for PNS complicated by PB in children.
Psychische Störungen nach erworbener ZNS-Schädigung
Authors: Aschenbrenner Steffen , Schilling Thomas M. , Grossmann Judith , Heck Tobias , Bossert Magdalena
Published: March 2021

Psychische Störungen sind eine häufige Folge erworbener zentralnervöser Schädigungen. Nicht frühzeitig erkannt und behandelt, wirken sie sich negativ auf den Verlauf der neurologischen Rehabilitation aus. Dieser Beitrag beschäftigt sich mit der Diagnostik und Therapie psychischer Störungen nach erworbener Schädigung des zentralen Nervensystems.
Veränderungen der Hepatitis-C-Virus-Genotyp-1a/1b-Verteilung zwischen 2004 und 2018 in Deutschland – eine Analyse von 17093 Patienten aus verschiedenen Real-World-Registern
Authors: Simon Karl-Georg , Serfert Yvonne , Buggisch Peter , Mauss Stefan , Boeker Klaus H.W. , Klinker Hartwig , Müller Tobias , Merle Uta , Hüppe Dietrich , Manns Michael P. , Wedemeyer Heiner
Published: March 2021

Einleitung Der Hepatitis C Genotyp 1 ist der häufigste Genotyp in West- und Zentraleuropa. In dieser Arbeit werden die Veränderungen der Baselinecharakteristika von 17 093 HCV-Patienten mit Genotyp 1a/1b, die im Zeitraum 2004–2018 in Deutschland antiviral therapiert wurden, analysiert. Es wurden insgesamt 5 Zeiträume betrachtet: (i) 2004–2007, (ii) 2008–2010, (iii) 2010–2013, (iv) 2014–2016, (v) 2017–2018.

Methoden Die vorliegende Analyse basiert auf 5 deutschlandweit durchgeführten nicht-interventionellen Registern und umfasst Daten von Patienten, die mit dem HCV-GT1a und HCV-GT1b infiziert waren und zwischen 2004 und 2018 dokumentiert wurden [ML17071, ML19464, ML21645, ML25724 (Peginterferon alfa-2a® non-interventional study (PAN)) und dem Deutschen Hepatitis-C-Register (DHC-R)].

Ergebnisse Im Untersuchungszeitraum (2004–2018) hatten 7662 Patienten eine HCV-GT1a- und 9431 Patienten eine HCV-GT-1b-Infektion. GT1a-Patienten waren im Vergleich zu GT1b-Patienten jünger (46,5 Jahre vs. 51,2 Jahre) und häufiger männlich (70 % vs. 52 %). Drogenkonsum in der Vorgeschichte oder derzeit war im Untersuchungszeitraum häufiger bei GT1a-Patienten mit höchster Frequenz im aktuellsten Zeitraum (2017–2018; 44 % GT1a, 10 % GT1b). Metabolische Komorbiditäten wie Übergewicht und Diabetes mellitus waren häufiger bei mit GT1b infizierten Frauen. Der Anteil des Genotyps 1a nahm von 34 % (Zeitraum 2004–2007) auf ca. 50 % (Zeitraum 2017–2018) relevant zu. 2004–2018 zeigte sich ein relevanter Wechsel des GT1a/1b-Quotienten bei Männern (2004–2007: 38 %/63 %; 2017–2018: 59 %/41 %) bei weitgehend konstantem GT1a-Anteil der Frauen von ca. 30 % deutschlandweit über alle 5 untersuchten Zeiträume.

Der Anteil der weiblichen Patienten mit GT1a in der Region Ost war im Vergleich zu den anderen 3 Regionen über nahezu alle Zeiträume niedriger, am deutlichsten ausgeprägt 2004–2007: 14 % GT1a vs. 86 % GT1b.

Zusammenfassung Im untersuchten Zeitraum (2004–2018) zeigte sich ein relevanter Anstieg der Genotyp-1a-Infektion bei Männern, nicht bei Frauen, assoziiert mit Drogenkonsum. Die Daten zeigen eine grundlegende Änderung in der HCV-Epidemiologie in Deutschland an, die Konsequenzen für das Therapiemanagement und die allgemeine Versorgung der Hepatitis-C-Patienten haben.
First German Guideline on Diagnostics and Therapy of Clinically Non-Functioning Pituitary Tumors
Authors: Deutschbein Timo , Jaursch-Hancke Cornelia , Knappe Ulrich J. , Saeger Wolfgang , Flitsch Jörg , Bojunga Jörg , Buchfelder Michael , Ditzen Beate , Gerlach Rüdiger , Gertzen Elfriede , Honegger Jürgen , Horstmann Gerhard A. , Koch Arend , Kreitschmann-Andermahr Ilonka , Kunz Mirjam , Lagrèze Wolf A. , Nicolay Nils H. , Paulus Werner , Reincke Martin , Schmidt Manuel A. , Weber Matthias M. , Wilhelm Helmut , Fassnacht Martin
Published: March 2021

Although non-functioning pituitary tumors are frequent, diagnostic and therapeutic concepts are not well standardized. We here present the first German multidisciplinary guideline on this topic. The single most important message is to manage the patients by a multidisciplinary team (consisting at least of an endocrinologist, a neurosurgeon, and a (neuro-) radiologist). The initial diagnostic work-up comprises a detailed characterization of both biochemical (focusing on hormonal excess or deficiency states) and morphological aspects (with magnetic resonance imaging of the sellar region). An ophthalmological examination is only needed in presence of symptoms or large tumors affecting the visual system. Asymptomatic, hormonally inactive tumors allow for a 'wait and scan' strategy. In contrast, surgical treatment by an experienced pituitary surgeon is standard of care in case of (impending) visual impairment. Therapeutic options for incompletely resected or recurrent tumors include re-operation, radiotherapy, and observation; the individual treatment plan should be developed multidisciplinary. Irrespective of the therapeutic approach applied, patients require long-term follow-up. Patient with larger pituitary tumors or former surgery/radiotherapy should be regularly counseled regarding potential symptoms of hormonal deficiency states.
Thymoquinone with Metformin Decreases Fasting, Post Prandial Glucose, and HbA1c in Type 2 Diabetic Patients
Authors: Ali Shoukath M. , Chen Paul , Sheikh Saifuddin , Ahmad Ateeq , Ahmad Moghis , Paithankar Mahesh , Desai Brijesh , Patel Piyush , Khan Mujtaba , Chaturvedi Alok , Patel Ronak , Panchal Dharmendra T. , Shah Kuntal , Chavda Vipul , Saboo Banshi D. , Patel Alpesh , Ahmad Imran
Published: March 2021

Objective Antihyperglycemic activity of Thymoquinone (TQ) was evaluated in diabetic mouse model and patients.

Methods TQ (50 mg/kg) was orally administered daily for 21 days in combination with metformin in diabetic mice and a reduction on blood glucose level was monitored. In human, a 90-day randomized study was carried out in 60 Type 2 Diabetes mellitus patients to evaluate safety and efficacy of TQ administration with metformin in a 3-arm study. Patients in arm 1 (T1) received 1 tablet of metformin SR 1000 mg and 1 tablet of TQ 50 mg once daily. The second arm (T2) patients received 1 tablet of metformin SR 1000 mg and 2 tablets of TQ 50 mg once daily. Patients in arm 3 (R) received 1 tablet of metformin SR 1000 mg only.

Results The diabetic mice treated with combination of TQ and metformin showed significant decrease in blood sugar compared to those treated with only metformin. In patients who completed the study, the glycated hemoglobin (HbA1c) values in T1, T2 and R decreased after 3 months from 7.2, 7.2 and 7.3 to 6.7, 6.8, and 7.1, respectively. A greater reduction in Fasting Blood Glucose and Post Prandial Blood Glucose was also observed in T1 and T2 arms compared to R.

Conclusion At dose levels of 50 and 100 mg of TQ combined with a daily dose of 1000 mg Metformin demonstrated a reduction in the levels of HbA1c and blood glucose compared to the standard treatment of diabetic patients with metformin alone.
Synthesis of Unsymmetrically Substituted Tetraphenylenes through Palladium-Catalyzed C(sp2)–H Activation
Authors: Zhang Yanghui , Wan Bin
Published: March 2021

An efficient protocol for the palladium-catalyzed cross-coupling reaction of 2-iodobiphenyls with biphenylene has been developed through C–H activation. The reaction provides a simple and efficient method for the synthesis of unsymmetrically substituted tetra­phenylenes.
Epidemiological Study of Patients with Spinal Cord Injury Treated in POLEM, a Specialized Clinic in São Paulo State – Brazil
Authors: Lopes José Eduardo de Andrade , Santos Karl Alex Patteis dos , Machado Caroline da Costa , Borges Meire Cristina , Coelho Eder Ferreira , Simões Ìris Lino Kemp , Pereira Ivone Mara , Dalera Mariele Torricelli Brunelli , Bertazini Talita Schneider de Camargo , Lopes José Eduardo de Andrade
Published: March 2021

Objective To analyze the epidemiological profile of patients with spinal cord injury treated at POLEM – Associação de Apoio às Pessoas com Lesão Medular (Association for Supporting People with Spinal Cord Injury).

Method The population studied comprised 113 patients with spinal cord injury, of traumatic or nontraumatic etiology, and the data obtained were compared with those of other institutions.

Results Of the 113 patients, 70.8% were male and 29.2% female. Traumatic lesions were responsible for 54% of the patients, and nontraumatic for 46%. Of the patients with traumatic injury, 90.2% were male, the main cause being traffic accidents. In nontraumatic lesions, women were the most affected, 51.9%; and dysraphism and myelitis were the main causes (31% and 21%, respectively).

Conclusion The results showed an important incidence of spinal cord injury due to trauma, mainly affecting young individuals of productive age and low educational level, representing high economic and social costs. The data found in the present study are similar to those of other studies performed in our country.
Low ADAMTS13 Activity Correlates with Increased Mortality in COVID-19 Patients
Authors: Sweeney Joseph M. , Barouqa Mohammad , Krause Gregory J. , Gonzalez-Lugo Jesus D. , Rahman Shafia , Gil Morayma Reyes
Published: March 2021

The causes of coagulopathy associated with coronavirus disease 2019 (COVID-19) are poorly understood. We aimed to investigate the relationship between von Willebrand factor (VWF) biomarkers, intravascular hemolysis, coagulation, and organ damage in COVID-19 patients and study their association with disease severity and mortality. We conducted a retrospective study of 181 hospitalized COVID-19 patients randomly selected with balanced distribution of survivors and nonsurvivors. Patients who died had significantly lower ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity, significantly elevated lactate dehydrogenase levels, significantly increased shistocyte/RBC fragment counts, and significantly elevated VWF antigen and activity levels compared with patients discharged alive. These biomarkers correlate with markedly elevated D-dimers. Additionally, only 30% of patients who had an ADAMTS13 activity level of less than 43% on admission survived, yet 60% of patients survived who had an ADAMTS13 activity level of greater than 43% on admission. In conclusion, COVID-19 may present with low ADAMTS13 activity in a subset of hospitalized patients. Presence of schistocytes/RBC fragment and elevated D-dimer on admission may warrant a work-up for ADAMTS13 activity and VWF antigen and activity levels. These findings indicate the need for future investigation to study the relationship between endothelial and coagulation activation and the efficacy of treatments aimed at prevention and/or amelioration of microangiopathy in COVID-19.
Vision Deterioration and Hydrocephalus: Rare Presentations of Vestibular Schwannoma and Evolution of Management
Authors: Keulen Marte van , Pace Jonathan , Burant Christopher J. , Penn David L. , Wilson Betsy , Ronald Andrew , Mowry Sarah E. , Megerian Cliff A. , Bambakidis Nicholas C.
Published: March 2021

Introduction The incidence of vestibular schwannoma is reported as 12 to 54 new cases per million per year, increasing over time. These patients usually present with unilateral sensorineural hearing loss, tinnitus, or vertigo. Rarely, these patients present with symptoms of hydrocephalus or vision changes.

Objective The study aimed to evaluate the surgical management of vestibular schwannoma at a single institution and to identify factors that may contribute to hydrocephalus, papilledema, and the need for pre-resection diversion of cerebrospinal fluid.

Patients and Methods A retrospective review examining the data of 203 patients with vestibular schwannoma managed with surgical resection from May 2008 to May 2020. We stratified patients into five different groups to analyze: tumors with a diameter of ≥40 mm, clinical evidence of hydrocephalus, and of papilledema, and patients who underwent pre-resection cerebrospinal fluid (CSF) diversion.

Results From May 2008 to May 2020, 203 patients were treated with surgical resection. Patients with tumors ≥40 mm were more likely to present with visual symptoms (p < 0.001). Presentation with hydrocephalus was associated with larger tumor size (p < 0.001) as well as concomitant visual symptoms and papilledema (p < 0.001). Patients with visual symptoms presented at a younger age (p = 0.002) and with larger tumors (p < 0.001).

Conclusion This case series highlights the rare presentation of vision changes and hydrocephalus in patients with vestibular schwannoma. We recommend urgent CSF diversion for patients with visual symptoms and hydrocephalus, followed by definitive resection. Further, vision may still deteriorate even after CSF diversion and tumor resection.
Croup: A Rare Manifestation of Coronavirus Disease 2019
Authors: Kumar H. C. Krishna , Kumar K. Jagadish , Nadagoud Shaarangdhar , VG Manjunath
Published: March 2021

Croup is an acute inflammatory condition affecting upper airways and commonly seen in children with younger age group. Croup is most commonly due to acute viral infection and rarely because of bacterial and atypical agents. Here, we report a 3-month-old child who presented to us with classic signs and symptoms of croup and was also positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Child's mother also tested positive for SARS-CoV-2. SARS-CoV-2 infection presenting with stridor and croup is very rare and probably represents a new manifestation which should be considered in a young infant presenting with croup.
Differences in Temporal Volume between Males and Females and the Influence of Age and BMI: A Cross-Sectional CT-Imaging Study
Authors: Nikolis Andreas , Frank Konstantin , Guryanov Robert , Gombolevskiy Victor , Morozov Sergey , Makhmud Kamal , Chernina Valeria , Gotkin Robert H. , Green Jeremy Blair , Cotofana Sebastian
Published: March 2021

Background The temple has been identified as one of the most compelling facial regions in which to seek aesthetic improvement—both locally and in the entire face—when injecting soft tissue fillers.

Objective The objective of this study is to identify influences of age, gender, and body mass index (BMI) on temporal parameters to better understand clinical observations and to identify optimal treatment strategies for treating temporal hollowing.

Methods The sample consisted of 28 male and 30 female individuals with a median age of 53 (34) years and a median BMI of 27.00 (6.94) kg/m2. The surface area of temporal skin, the surface area of temporal bones, and the temporal soft tissue volume were measured utilizing postprocessed computed tomography (CT) images via the Hausdorff minimal distance algorithm. Differences between the investigated participants related to age, BMI, and gender were calculated.

Results Median skin surface area was greater in males compared with females 5,100.5 (708) mm2 versus 4,208.5 (893) mm2 (p < 0.001) as was the median bone surface area 5,329 (690) mm2 versus 4,477 (888) mm2 (p < 0.001). Males had on average 11.04 mL greater temporal soft tissue volume compared with age and BMI-matched females with p < 0.001. Comparing the volume between premenopausal versus postmenopausal females, the median temporal soft tissue volume was 46.63 mL (11.94) versus 40.32 mL (5.69) (p = 0.014).

Conclusion The results of this cross-sectional CT imaging study confirmed previous clinical and anatomical observations and added numerical evidence to those observations for a better clinical integration of the data.
Collisions of neutral gas with dusty plasma support explanations of natural phenomena in Earth’s ionosphere
Authors: Johnson-Groh Mara
Published: March 2021

Mathematical model of dusty ionospheric plasma leads to better understanding how neutral collisions with charged particles affect modulational instabilities in the region.
Video-based fractional order identification of diffusion dynamics for the analysis of migration rates of polar and nonpolar liquids: Water and oil studies
Authors: Andrade Stefani I. E. , Galvão Roberto K. H. , Araujo Mario C. U. , Hadjiloucas Sillas
Published: March 2021

Diffusion dynamics of water and oil are observed in real-time using video images. Savitzky–Golay derivative filtering ensures accurate localization of the liquid front. System identification demonstrates that a fractional-order model with only two parameters may be used to describe the dynamics of the diffusion process. The method paves the way for video-based cellulose filter paper microfluidics and lateral flow assays, which are low cost and have broad diagnostic applications.
Stability of saturated granular columns: Role of stress-dilatancy and capillarity
Authors: Taylor-Noonan A. M. , Siemens G. A. , Cabrera M. A. , Arpin N. M. , Parera Morales F. , Take W. A.
Published: March 2021

The granular column collapse experiment is an important benchmark case for the physical and numerical study of transitional mass flows. Unlike columns of dry granular materials, the presence of a relatively incompressible fluid, such as water, in the voids of saturated columns complicates the shear behavior of the column by becoming a function of the coupled shear and volumetric behavior of the grain–fluid system. Dilative or contractive behavior at the pore level will cause a decrease or increase, respectively, in the pore fluid pressure. These changes in effective stress, in turn, will define stability or instability and length of runout. Here we use the new opportunity provided by transparent soil to observe air entry within saturated columns to explore the hypothesis that the entry pressure provides the maximum contribution of capillary pressure at incipient failure, thereby providing a quantitative control on the stability of dilative granular columns. Furthermore, the mobility of densely packed saturated columns subject to collapse was significantly influenced by air entry. An analytical model, based on this assumption of limiting capillary pressure, is able to describe the stability of the experimental columns as well as the larger dataset from the literature, reframing the previous empirical stability threshold using limit equilibrium and soil material parameters. Our results demonstrate the importance of stress-dilatancy and air-entry phenomena on the rapid shear behavior of saturated granular materials.
Effect of polymer swell in extrusion foaming of low-density polyethylene
Authors: Lombardi Lorenzo , Tammaro Daniele
Published: March 2021

Insights into the effect of die swell on extrusion foam of thermoplastic polymers are presented. The die swell or Barus effect is the swelling of a viscoelastic material due to a fast elastic recovery after being subjected to stress. The elastic recovery is proportional to the energy stored in the material during the deformation that is released immediately when the material is free to expand. In extrusion foam, the elastic recovery happens at the die exit together with the foaming process (i.e., bubble nucleation and growth). Previous reports on extrusion have focused on modeling the die swell or foaming individually. We investigated the existence of a link between the die swell and foaming that is fundamental in designing the geometry of a die for extrusion foam. Simple and complex dies were used to measure the expansion ratio of a polyethylene blown with isobutane and CO2. It was found that the expansion ratio is anisotropic, the anisotropy in the expansion of the foam is due to the die swell strongly affecting the final shape of the product, and it cannot be neglected in standard application for extrusion foam. Surprisingly, it was found that the foam density changes at a high level of die swell because it is affected by the elastic recovery of the material.
Light–matter interaction of a molecule in a dissipative cavity from first principles
Authors: Wang Derek S. , Neuman Tomáš , Flick Johannes , Narang Prineha
Published: March 2021

Cavity-mediated light–matter coupling can dramatically alter opto-electronic and physico-chemical properties of a molecule. Ab initio theoretical predictions of these systems need to combine non-perturbative, many-body electronic structure theory-based methods with cavity quantum electrodynamics and theories of open-quantum systems. Here, we generalize quantum-electrodynamical density functional theory to account for dissipative dynamics of the cavity and describe coupled cavity–single molecule interactions in the weak-to-strong-coupling regimes. Specifically, to establish this generalized technique, we study excited-state dynamics and spectral responses of benzene and toluene under weak-to-strong light–matter coupling. By tuning the coupling, we achieve cavity-mediated energy transfer between electronically excited states. This generalized ab initio quantum-electrodynamical density functional theory treatment can be naturally extended to describe cavity-mediated interactions in arbitrary electromagnetic environments, accessing correlated light–matter observables and thereby closing the gap between electronic structure theory, quantum optics, and nanophotonics.
Leaky cell model of hard spheres
Authors: Fai Thomas G. , Taylor Jamie M. , Virga Epifanio G. , Zheng Xiaoyu , Palffy-Muhoray Peter
Published: March 2021

We study packings of hard spheres on lattices. The partition function, and therefore the pressure, may be written solely in terms of the accessible free volume, i.e., the volume of space that a sphere can explore without touching another sphere. We compute these free volumes using a leaky cell model, in which the accessible space accounts for the possibility that spheres may escape from the local cage of lattice neighbors. We describe how elementary geometry may be used to calculate the free volume exactly for this leaky cell model in two- and three-dimensional lattice packings and compare the results to the well-known Carnahan–Starling and Percus–Yevick liquid models. We provide formulas for the free volumes of various lattices and use the common tangent construction to identify several phase transitions between them in the leaky cell regime, indicating the possibility of coexistence in crystalline materials.
Multi-scale dynamics simulations of molecular polaritons: The effect of multiple cavity modes on polariton relaxation
Authors: Tichauer Ruth H. , Feist Johannes , Groenhof Gerrit
Published: March 2021

Coupling molecules to the confined light modes of an optical cavity is showing great promise for manipulating chemical reactions. However, to fully exploit this principle and use cavities as a new tool for controlling chemistry, a complete understanding of the effects of strong light–matter coupling on molecular dynamics and reactivity is required. While quantum chemistry can provide atomistic insight into the reactivity of uncoupled molecules, the possibilities to also explore strongly coupled systems are still rather limited due to the challenges associated with an accurate description of the cavity in such calculations. Despite recent progress in introducing strong coupling effects into quantum chemistry calculations, applications are mostly restricted to single or simplified molecules in ideal lossless cavities that support a single light mode only. However, even if commonly used planar mirror micro-cavities are characterized by a fundamental mode with a frequency determined by the distance between the mirrors, the cavity energy also depends on the wave vector of the incident light rays. To account for this dependency, called cavity dispersion, in atomistic simulations of molecules in optical cavities, we have extended our multi-scale molecular dynamics model for strongly coupled molecular ensembles to include multiple confined light modes. To validate the new model, we have performed simulations of up to 512 Rhodamine molecules in red-detuned Fabry–Pérot cavities. The results of our simulations suggest that after resonant excitation into the upper polariton at a fixed wave vector, or incidence angle, the coupled cavity-molecule system rapidly decays into dark states that lack dispersion. Slower relaxation from the dark state manifold into both the upper and lower bright polaritons causes observable photo-luminescence from the molecule–cavity system along the two polariton dispersion branches that ultimately evolves toward the bottom of the lower polariton branch, in line with experimental observations. We anticipate that the more realistic cavity description in our approach will help to better understand and predict how cavities can modify molecular properties.
Quantum dots as potential sources of strongly entangled photons: Perspectives and challenges for applications in quantum networks
Authors: Schimpf Christian , Reindl Marcus , Basso Basset Francesco , Jöns Klaus D. , Trotta Rinaldo , Rastelli Armando
Published: March 2021

The generation and long-haul transmission of highly entangled photon pairs is a cornerstone of emerging photonic quantum technologies with key applications such as quantum key distribution and distributed quantum computing. However, a natural limit for the maximum transmission distance is inevitably set by attenuation in the medium. A network of quantum repeaters containing multiple sources of entangled photons would allow overcoming this limit. For this purpose, the requirements on the source's brightness and the photon pairs' degree of entanglement and indistinguishability are stringent. Despite the impressive progress made so far, a definitive scalable photon source fulfilling such requirements is still being sought after. Semiconductor quantum dots excel in this context as sub-Poissonian sources of polarization entangled photon pairs. In this work, we present the state-of-the-art set by GaAs based quantum dots and use them as a benchmark to discuss the challenges toward the realization of practical quantum networks.
Will flat optics appear in everyday life anytime soon?
Authors: Chen Wei Ting , Capasso Federico
Published: March 2021

Flat optical components based on metasurfaces will appear in our daily life in the near future. Our discussion focuses on metasurface-based components consisting of sub-wavelength spaced dielectric nanostructures in the optical region. After an introduction to the underlying technology, the advantages of metasurfaces are highlighted and the efforts in the development of metasurface components is discussed. The metasurface not only promises a reduction in the size and complexity of optical components but also brings new functionalities. Examples of achromatic optical components, a full-Stokes metasurface camera, and a metasurface depth sensor with superior performance are highlighted. Finally, future trends and opportunities are discussed.
Some aspects of modulational interaction in Earth's dusty ionosphere
Authors: Morozova T. I. , Kopnin S. I. , Popel S. I. , Borisov N. D.
Published: March 2021

The development of modulational instability involving dust acoustic perturbations in dusty ionospheric plasma and in dusty plasmas of meteor tails in Earth's ionosphere was considered. The effect of collisions of electrons, ions, and dust grains with neutrals at different altitudes was estimated. It is shown that, in this case, the influence of collisions of electrons and ions with neutrals is usually less significant than the influence of collisions between dust grains and neutrals. It is demonstrated that the effect of the modulational instability on the propagation of electromagnetic waves in the dusty ionospheric plasma is the most significant at heights of 100–120 km. The values of the wave vectors of the electromagnetic pump wave at which inelastic collisions with neutrals are important for the development of modulational interaction are calculated. The modulational interaction in the dusty ionosphere is important for the explanation of different phenomena such as ground-based observations of low-frequency ionospheric radio noises with frequencies below 60 Hz. The absence of observations of low-frequency ionospheric radio noise during such phenomena as noctilucent clouds and polar mesosphere summer echoes caused by the presence of dusty plasmas at heights of 80–95 km is explained by suppression of the development of the modulational instability at these heights. The role of inelastic collisions with neutrals in meteor tails is also discussed. It is shown that for typical parameters of dusty plasmas of meteor tails such collisions do not influence the development of the modulation instability in meteor tails.
The rectification mechanism in polyelectrolyte gel diodes
Authors: Nyamayaro Kudzanai , Triandafilidi Vasilii , Keyvani Parya , Rottler Joerg , Mehrkhodavandi Parisa , Hatzikiriakos Savvas G.
Published: March 2021

Ionic driven devices have been increasingly investigated in the drive to develop flexible and biointegrable electronics. One such device is a polyelectrolyte gel diode capable of rectifying ionic current. However, the underlying mechanism behind the rectification of current in polyelectrolyte gel diodes is not fully understood. Based on experimental data, it has been proposed that the rectification is due to the asymmetric distribution of ions at the interface between two gels doped with a cationic polyelectrolyte on one side and an anionic polyelectrolyte on the other. Additionally, an electrochemical model has been proposed to explain the mechanism quantitatively. Here, we explore the mechanism proposed by the Yamamoto–Doi model and validate it by using experimental data. We show that the diode operates via a physical mechanism that involves the electrochemical generation of proton and hydroxyl ions at the electrodes to generate current. Exponential currents (J) in the forward bias were observed and J=A−V (with A inversely proportional to the gel ionization and V the potential) in the backward bias, which coincides with predictions of the electrochemical Yamamoto–Doi model. Additionally, we also confirm the dependence of the electrochemical model on the dopant concentration in the backward bias regime.
Phase behavior of hard cylinders
Authors: Lopes Joyce T. , Romano Flavio , Grelet Eric , Franco Luís F. M. , Giacometti Achille
Published: March 2021

Using isobaric Monte Carlo simulations, we map out the entire phase diagram of a system of hard cylindrical particles of length (L) and diameter (D) using an improved algorithm to identify the overlap condition between two cylinders. Both the prolate L/D > 1 and the oblate L/D < 1 phase diagrams are reported with no solution of continuity. In the prolate L/D > 1 case, we find intermediate nematic N and smectic SmA phases in addition to a low density isotropic I and a high density crystal X phase with I–N-SmA and I-SmA-X triple points. An apparent columnar phase C is shown to be metastable, as in the case of spherocylinders. In the oblate L/D < 1 case, we find stable intermediate cubatic (Cub), nematic (N), and columnar (C) phases with I–N-Cub, N-Cub-C, and I-Cub-C triple points. Comparison with previous numerical and analytical studies is discussed. The present study, accounting for the explicit cylindrical shape, paves the way to more sophisticated models with important biological applications, such as viruses and nucleosomes.
Dynamic mode decomposition based analysis of flow past a transversely oscillating cylinder
Authors: Ping Huan , Zhu Hongbo , Zhang Kai , Zhou Dai , Bao Yan , Xu Yuwang , Han Zhaolong
Published: March 2021

Three-dimensional numerical computations are carried out for a cylinder undergoing controlled sinusoidal oscillation perpendicular to the free stream. The results are examined for Re = 500 and an oscillation amplitude of A/D=0.25, to allow comparison with the two-dimensional study by Blackburn and Henderson [J. Fluid Mech. 385, 255–286 (1999)]. The dynamic response of the flow is investigated over a wide oscillation frequency range from 0.5fo to 1.5fo, with fo being the natural shedding frequency of the fixed cylinder. As the oscillation frequency passes through fo, the ubiquitous abrupt shift in the phase of vortex shedding is again observed. On either side of this shift, the wakes exhibit Kármán mode of shedding, in the absence of the mode switch. The hypothesis for the mechanism of phase shift proposed by Blackburn and Henderson [J. Fluid Mech. 385, 255–286 (1999)] is further examined by quantitatively measuring the flux of vorticity generated on the base of the cylinder. Unlike in two-dimensional flow, where hysteresis is found to be associated with four branches, in three-dimensional flow only two longer branches K1 and K2 are identified, which bring out a remarkably simplified bifurcation structure. Dynamic mode decomposition (DMD) and its sparsity-promoting variant are used to characterize the coherent modes that govern the dynamics of the flow, as well as their corresponding frequencies. For the non-synchronized case, a multitude of DMD modes must be retained to accurately approximate the original flow, while for the synchronized case, only four DMD modes suffice to guarantee a same performance loss. In addition, the DMD modes that have the most profound impact on the hysteresis of lift and drag fluctuations are identified by DMD reconstruction.
Comparing plasma conditions in short-pulse-heated foils via fine-structure x-ray emission
Authors: Kraus B. F. , Chien A. , Gao Lan , Hill K. W. , Bitter M. , Efthimion P. C. , Chen Hui , Schneider M. B. , Moreau A. , Hollinger R. , Wang Shoujun , Song Huanyu , Rocca J. J.
Published: March 2021

Fine-structure x-ray spectra have been measured from foils with embedded tracer layers at two laser facilities. A suite of layered foils with thin Ti tracers under varied tamper layers was studied at both the Titan and the ALEPH 400 nm laser facilities, where Ti Heα emission was recorded using a high-resolution Bragg crystal spectrometer. Several indicators of plasma parameters are examined in the spectra, including temperature- and density-dependent line ratios and line broadening from Stark and opacity effects. Spectra indicate that (1) the plasma density at ALEPH is significantly higher than at Titan and (2) the electron temperature is high for near-surface layers at both facilities but drops more quickly with depth at ALEPH. These inferences of plasma conditions are consistent with differing levels of temporal contrast at each laser facility.
Determining the hydration free energies of selected small molecules with MP2 and local MP2 through adaptive force matching
Authors: Zheng Dong , Yuan Ying , Wang Feng
Published: March 2021

Force fields for seven small solute molecules, ethanol, 2-methyl-1-propanol, 2-butanol, cyclohexene, tetrahydropyran, 1,4-dioxane, and 1,4-butanediol, in dilute aqueous solutions were created with the adaptive force matching (AFM) method using MP2 or local MP2 as reference. The force fields provide a way to predict the hydration free energies (HFEs) of these molecules with only electronic structure calculations as reference. For six of the seven molecules, the predicted HFEs are in very good agreement with experiments. For 1,4-butanediol, the model created by force matching LMP2 provides a HFE that is too positive. Further investigation suggests that LMP2 may not be sufficiently accurate for computing HFEs for alcohols with AFM. Other properties, such as enthalpy of hydration, diffusion constants, and vibrational spectra, are also computed with the force field developed. The force fields developed by AFM provide a bridge for computing ensemble properties of the reference electronic structure method. With MP2 and LMP2 as reference methods, the computed properties of the small molecular solutes are found to be in good agreement with experiments.
Asymmetric vortex sheet
Authors: Migdal Alexander
Published: March 2021

We present a steady analytical solution of the incompressible Navier–Stokes equation for arbitrary viscosity in an arbitrary dimension d of space. It represents a d − 1 dimensional vortex “sheet” with an asymmetric profile of vorticity as a function of the normal coordinate z. This profile is related to the Hermite polynomials Hμ(z), which are analytically continued to the negative fractional index μ=−dd−1. In d = 2 dimensions, the solution degenerates to a constant vorticity flow. In d≥3 dimensions, the vorticity is confined to the thin layer around the hyperplane with Gaussian decay on one side of the hyperplane and the power decay on another side. One can adjust the common scale of velocity so that the dissipation will stay finite at vanishing viscosity. In this limit, the width w of the viscous lawyer will shrink to zero as ν35 for arbitrary dimension d >3. In d = 3 dimensions, this power law is also accompanied by powers of the logarithm.