bluuebunny/crossref_metadata_2025 huggingface dataset:
Hemifacial Spasm Associated with Chiari Type I Malformation: Surgical Considerations and Case Report
Authors: Lobão Carlos Augusto Ferreira , Sousa Ulysses de Oliveira , Cabral Diego Arthur Castro , Campos Fernanda Myllena Sousa
Published: April 2020

Hemifacial spasm (HS) is a movement disorder characterized by paroxysmal and irregular contractions of the muscles innervated by the facial nerve. Chiari malformation type I (CM I) is a congenital disease characterized by caudal migration of the cerebellar tonsils, and surgical decompression of foramen magnum structures has been used for treatment. The association of HS with CM I is rare, and its pathophysiology and therapeutics are speculative. There are only a few cases reported in the literature concerning this association. The decompression of the posterior fossa for the treatment of CM I has been reported to relieve the symptoms of HS, suggesting a relation between these diseases. However, the possible complications of posterior fossa surgery cannot be underrated. We report the case of a 66-year-old patient, in ambulatory follow-up due to right HS, no longer responding to botulinum toxin treatment. Magnetic resonance imaging (MRI) of the skull revealed compression of the facial nerve and CM I. The patient underwent surgery for HS by neurovascular microdecompression of the facial nerve via right lateral suboccipital craniectomy, but presented significant clinical worsening in the postoperative period even though the cerebellum edema related to surgical manipulation was mild. Due to the clinical worsening, the patient underwent a median suboccipital craniectomy with decompression of the foramen magnum structures. After this second surgery, the patient had progressive improvement and was discharged from the hospital for ambulatory care.
Role of Fine Needle Aspiration Cytology in the Diagnosis of Parotid Gland Tumors: Analysis of 193 Cases
Authors: Dhanani Rahim , Iftikhar Haissan , Awan Muhammad Sohail , Zahid Nida , Momin Sehrish Nizar Ali
Published: April 2020

Introduction Parotid gland tumors include a wide variety of inflammatory and neoplastic diseases. The majority of these tumors are benign (80%), which usually require superficial parotidectomy, while the incidence of malignant tumors is lower (20%), requiring more radical surgery with or without neck dissection. The diagnosis cannot be established on the basis of clinical history and simple physical examination and requires complementary diagnostic methods. Fine needle aspiration cytology (FNAC) guided by ultrasound is a widely used diagnostic tool to evaluate parotid swellings.

Objective To determine the sensitivity, specificity, positive and negative predictive values and diagnostic accuracy of FNAC in the diagnosis of parotid gland tumors.

Methods A retrospective chart review of 193 patients who underwent preoperative FNAC and parotidectomy at the Aga Khan University Hospital, Karachi, Pakistan, from the period of January 2000 to December 2015 was performed.

Results Out of 193 patients undergoing parotidectomy, 110 (57%) were males and 83 (43%) were females, the mean age being 48.21 and 43.76 years old, respectively. The mean duration of the symptoms was 41.33 months, and the most common symptom was preauricular swelling present in all patients, followed by pain, which was present in 29 patients (15%) and facial nerve weakness in 6 patients (3.1%). Fine needle aspiration cytology was performed preoperatively and the results were compared with the final histopathology, which showed sensitivity of 88.9%, specificity of 97.9%, positive predictive value of 93%, negative predictive value of 96.7% and diagnostic accuracy of 95.8%.

Conclusion Our results suggest that FNAC is relatively an accurate method for preoperative diagnosis of parotid swelling and can prove to be a valuable tool for preoperative counseling of the nature of the disease and prognosis.
Submental Artery Island Flap in Oral Cavity Reconstruction. An Observational, Retrospective Two-centre Study
Authors: Ramirez Adonis Tupac , Chiesa-Estomba Carlos Miguel , González-García José Ángel
Published: April 2020

Introduction The submental flap provides an alternative technique in orofacial reconstruction, especially in situations in which free flaps are not available, or the patients are unfit.

Objective To demonstrate the oncological safety and benefits of this flap in oral cavity reconstruction.

Methods A total of 14 patients with oral cavity cancers, who underwent submental flap reconstruction from January 2016 to January 2018, were included in the study.

Results There were 11 male and 3 female patients with a mean age of 66.7 ± 14 (Min: 52/Max: 91) years old. The most common primary tumor site was the mobile tongue in 12 (85.7%) patients. All of the patients underwent ipsilateral selective neck dissection after the flap was harvested. Flap partial necrosis was observed in one patient, and total necrosis in another one. The mean follow-up was of one year. Nonlocal or regional recurrences were observed.

Conclusion Submental island flap represents a good option in oral cavity reconstruction in a restricted setting or in patients considered not fit for free flap reconstruction. Preoperative selection of clinically neck node-negative patients is essential due to the potential risk of occult metastasis.
The Maternal Impact, Health Burden, and Postpartum Sequela in Triplet Pregnancies: A Retrospective Cohort
Authors: Lambers Donna S. , Allen Jennifer , Gottula Jessica , Devaiah C. Ganga , Habli Mounira
Published: April 2020

Objective The aim of the study is to describe the maternal health burden and perinatal outcomes in triplet pregnancies, and identify the maternal and pregnancy indicators associated with increased perinatal morbidity and mortality.

Study Design This is a retrospective cohort study of triplet pregnancies from 2007 to 2014. Maternal data were manually collected and assessed until 6 weeks postpartum, and neonatal data were assessed until hospital discharge or death.

Results Eighty-two triplet pregnancies were identified with 246 babies born. Mean gestational age at delivery was 32.3 (standard deviation [SD] ± 3.6) weeks and average birth weight was 1,726 g (SD ± 500). There were 12 perinatal deaths and 25 (10.2%) infants diagnosed with a congenital anomaly. Prior preterm birth and nulliparity had a negative impact on gestational age at delivery (p = 0.016) as compared with prior full-term births. Pregnancy complications (preeclampsia or hypertensive disorders [46.3%], gestational diabetes [28%], postpartum hemorrhage [9.8%], and blood transfusions [8.5%]) also impacted gestational age at delivery (33.0 vs. 34.0 weeks, p = 0.031). Spontaneous conception, chorionicity, and maternal medical problems did not have an impact on median gestational age.

Conclusion Nulliparity and presence of pregnancy complications are pertinent to triplet outcomes. This study provides valuable information for anticipatory guidance and preconception counseling to patients considering artificial reproductive technology.
Congenital Complete Atrioventricular Heart Block in a Pregnant Woman with Sjögren Syndrome: Prenatal Care Follow-Up and the Challenge of Intrauterine Treatment
Authors: Carrilho Milene Carvalho , Bravo-Valenzuela Nathalie Jeanne , Araujo Júnior Edward
Published: April 2020

The present report describes a case of complete atrioventricular block (CAVB) diagnosed at 25 weeks of gestation in a pregnant woman with Sjögren's syndrome and positive anti-Ro/SSA antibodies. Fluorinated steroids (dexamethasone and betamethasone) and terbuline were used to increase the fetal heart rate, but the fetal heart block was not reversible, and the administration of drugs was discontinued due to maternal collateral effects. Follow-up fetal echocardiograms were performed, and the fetus evolved with pericardial effusion, presence of fibroelastosis in the right ventricle, and ventricular dysfunction. Interruption of pregnancy by cesarean section was indicated at 34 weeks of gestation, and a cardiac pacemaker was implanted in the male newborn immediately after birth. Therapy for fetuses with CAVB is controversial mainly regarding the use or not of corticosteroids; however, monitoring of the atrioventricular interval by fetal echocardiography should be performed in fetuses from pregnant women with positive autoantibodies anti-Ro/SSA and/or anti-La/SSB to prevent the progression to CAVB.
Microsurgical and Endoscopic Anatomy of the Cavernous Sinus
Authors: Isolan Gustavo Rassier , Braga Francisco Luiz Souza , Campero Alvaro , Landeiro José Alberto , de Araújo Ricardo Marques Lopes , Adjer Pablo , Sakaya Gabriel Reis , Rabelo Nícollas Nunes , Brito Josué da Silva , Teixeira Manoel Jacobsen , Figueiredo Eberval Gadelha
Published: April 2020

Objective To describe the endoscopic and microsurgical anatomy of the cavernous sinus (CS) with focus on the surgical landmarks in microsurgical anatomy.

Materials and methods Ten formalin-fixed central skull base specimens (20 CSs) with silicone-injected carotid arteries were examined through an extended endoscopic transsphenoidal approach. Fifteen formalin-fixed heads were dissected to simulate the surgical position in CS approaches.

Results Endoscopic access enables identification of the anterior and posterior surgical corridors. Structures within the CS and on its lateral wall could be visualized and studied, but none of the triangular areas relevant to the transcranial microsurgical anatomy were fully visible through the endoscopic approach.

Conclusion The endoscopic approach to the CS is an important surgical technique for the treatment of pathological conditions that affect this region. Correlating endoscopic findings with the conventional (transcranial) microsurgical anatomy is a useful way of applying the established knowledge into a more recent operative technique. Endoscope can provide access to the CS and to the structures it harbors.
Impact of Helium-Oxygen Administered via High Velocity Nasal Insufflation on Delivery of Inhaled Nitric Oxide
Authors: Hertzog James H. , Burr Katlyn L. , Stump Angela , Brown Joel M. , Penfil Scott , McMahon Kimberly
Published: April 2020

Inhaled nitric oxide (iNO) may be continued during the transition from invasive to noninvasive respiratory support. Upper airway obstruction from laryngeal edema following extubation and lower airway obstruction from asthma and bronchiolitis may be managed with inhaled helium. The coadministration of helium with iNO and the impact on delivered amounts of iNO have not been extensively studied. A bench model simulating a spontaneously breathing infant received iNO at varying preset doses delivered with either helium-oxygen or nitrogen-oxygen via a Vapotherm unit. iNO levels were measured at the simulated trachea. Results from the two conditions were compared using t-tests. When nitrogen-oxygen was used, there was no difference between preset and measured iNO levels. A significant difference was present when helium-oxygen was used, with a 10-fold increase in measured iNO levels compared with preset values. The use of helium resulted in a significant increase in measured iNO at the level of the simulated trachea. Clinicians must be aware that iNO will not be delivered at prescribed doses when used with helium under the conditions used in this study.
Passivating contacts and tandem concepts: Approaches for the highest silicon-based solar cell efficiencies
Authors: Hermle Martin , Feldmann Frank , Bivour Martin , Goldschmidt Jan Christoph , Glunz Stefan W.
Published: April 2020

The efficiency of photovoltaic energy conversion is a decisive factor for low-cost electricity from renewable energies. In recent years, the efficiency of crystalline silicon solar cells in mass production has increased annually by about 0.5–0.6%abs per year. In order to maintain this development speed, new technologies must be developed and transferred to industrial production. After the transition from full area Al back surface field cells to passivated emitter and rear contact cells, passivating contacts are an important step to get as close as possible to the efficiency limit of single junction Si solar cells. The theoretical background and the two prominent technologies for passivating contacts are presented and discussed. After implementing passivating contacts, the fundamental limit of single junction Si solar cells of 29.4% is in reach. Multi-junction solar cells are the most promising option to achieve efficiencies greater than 30%. Tandem technologies based on crystalline silicon as bottom cells have the advantage that they are based on a mature technology established on a gigawatt scale and can partially use the existing production capacity. In addition, silicon has an ideal bandgap for the lower subcell of a tandem solar cell. The two most promising material candidates for the top cell, i.e., III/V and perovskites, will be discussed. The presented technology routes show that silicon is able to maintain its outstanding position in photovoltaics in the coming years.
Wave-induced vortex generation around a slender vertical cylinder
Authors: Antolloni Giulia , Jensen Atle , Grue John , Riise Bjørn H. , Brocchini Maurizio
Published: April 2020

Experimental results of wave-induced vortex generation around a slender, vertical cylinder are discussed. Coherent vortices appear in long waves (kR ∼ 0.1, where k is the wave number and R is the cylinder radius) during the timing of the secondary load cycle, a strongly nonlinear component of the wave force acting on the cylinder, which is also measured. However, the secondary load cycle is also present in moderately long wave cases (kR ∼ 0.3) where there is no vortex formation. The measurement of vortex generation is enabled by particle image velocimetry. The flow downstream the cylinder, in three horizontal planes at different depths, is measured. The vortex formation that occurs in the long waves is attached to the cylinder in the form of thin vortex tubes. These appear symmetrically at angles of 40°–45° off the wave propagation direction. In one weak long wave case, several very thin vortex tubes appear along the back side of the cylinder. Vortex diameters are 20% of the cylinder diameter in four cases and 50% of the cylinder diameter in one case. The measured vorticity emanates from the cylinder’s boundary layer and is an order of magnitude stronger than the vorticity caused by wave breaking. Wave breaking reduces the vortex strength. The fact that the secondary load cycle appears without and with flow separation effects indicates that the load cycle is a gravity wave phenomenon that scales with the Froude number but that flow separation effects also contribute to the magnitude of such suction forces.
How motifs condition critical thresholds for tipping cascades in complex networks: Linking micro- to macro-scales
Authors: Wunderling Nico , Stumpf Benedikt , Krönke Jonathan , Staal Arie , Tuinenburg Obbe A. , Winkelmann Ricarda , Donges Jonathan F.
Published: April 2020

In this study, we investigate how specific micro-interaction structures (motifs) affect the occurrence of tipping cascades on networks of stylized tipping elements. We compare the properties of cascades in Erdős–Rényi networks and an exemplary moisture recycling network of the Amazon rainforest. Within these networks, decisive small-scale motifs are the feed forward loop, the secondary feed forward loop, the zero loop, and the neighboring loop. Of all motifs, the feed forward loop motif stands out in tipping cascades since it decreases the critical coupling strength necessary to initiate a cascade more than the other motifs. We find that for this motif, the reduction of critical coupling strength is 11% less than the critical coupling of a pair of tipping elements. For highly connected networks, our analysis reveals that coupled feed forward loops coincide with a strong 90% decrease in the critical coupling strength. For the highly clustered moisture recycling network in the Amazon, we observe regions of a very high motif occurrence for each of the four investigated motifs, suggesting that these regions are more vulnerable. The occurrence of motifs is found to be one order of magnitude higher than in a random Erdős–Rényi network. This emphasizes the importance of local interaction structures for the emergence of global cascades and the stability of the network as a whole.
A levitated magnetic dipole configuration as a compact charged particle trap
Authors: Saitoh H. , Stoneking M. R. , Pedersen T. Sunn
Published: April 2020

As a magnetic confinement configuration for electron–positron pair-plasmas, the APEX collaboration [T. S. Pedersen et al., New J. Phys. 14, 035010 (2012)] plans to construct a compact levitated dipole experiment with a high-temperature superconducting coil. In order to realize stable levitation of the dipole field coil, a simple feedback-controlled levitation system was constructed with conventional analog circuits. We report the properties of a prototype levitation system using a permanent magnet and compare its behavior to predictions from a stability analysis. We also present a practical review needed for the construction of a compact levitated dipole trap system based on the work of Morikawa et al. [Teion Kogaku, J. Cryo. Soc. Jpn. 39, 209 (2004)]. Numerical orbit analysis suggests improved confinement properties of charged particles in a dipole field trap by replacing the permanent magnet with a levitated superconducting coil magnet. Such a compact dipole field configuration is potentially applicable to the confinement of various charged particles including positrons and electrons.
Adsorption and isomerization of glyoxal and methylglyoxal at the air/hydroxylated silica surface
Authors: Gladich Ivan , Carignano Marcelo A. , Francisco Joseph S.
Published: April 2020

We present results from molecular dynamics simulations coupled with enhanced sampling techniques on the adsorption and isomerization of glyoxal (GL) and methylglyoxal (MG) at the air/hydroxylated silica (α-Quartz) interface. GL and MG are two organic compounds present in the atmosphere as oxidation products of both biogenic and anthropogenic precursors. By adsorption and hydration on liquid droplets or wetted dust particles, they can enable aerosol growth in the atmosphere. Moreover, thanks to the different polar characters of their trans and cis conformers, GL and MG have been suggested as possible molecular switches capable of responding to changes in solvent polarity. Here, we show that the hydroxylated silica surface does not significantly catalyze the trans-to-cis isomerization, but it stabilizes the cis-isomers, indicating a higher interfacial cis/trans relative concentration compared to the gas phase. Moreover, adsorbed GL prefers to lie parallel on the silica surface, while adsorbed MG shows a tilted orientation. In particular, we report the aldehyde group pointing upward (downward) to the gas phase (to the silica surface) in trans-MG (cis-MG). These results will help in the rationalization of upcoming experimental and modeling work on the adsorption of ketonic compounds on dust aerosols, while it clarifies the catalytic role of the solid substrate surface in promoting conformational changes.
Time-dependent Ginzburg-Landau simulations of superconducting vortices in three dimensions
Authors: Lara Antonio , González-Ruano César , Aliev Farkhad G.
Published: April 2020

Here we describe the development of a computer algorithm to simulate the Time-Dependent Ginzburg-Landau equation (TDGL) and its application to understand superconducting vortex dynamics in confined geometries. Our initial motivation to get involved in this task was trying to understand better our experimental measurements on the dynamics of superconductors with vortices at high frequencies leading to microwave stimulated superconductivity due to the presence of vortex [A. Lara, et al., Sci. Rep. 5, 9187 (2015)].
Catastrophe theory in the phenomenological description of the avalanche effect in dc-biased microwave HTSC transmission lines
Authors: Melnyk S. I. , Melnyk S. S. , Lavrinovich A. A. , Cherpak N. T.
Published: April 2020

Within the framework of the proposed generalization of the phenomenological model of a microwave nonlinear HTSC transmission line, the effects of direct current on the transmission line are studied. Taking into account the next term in the expansion of the nonlinear dependence of the resistance on current allows us to explain the anomalous dependence of the insertion loss on the input power level observed in the experiment at subcritical temperatures. An additional direct current through the microwave waveguide can lead to the appearance of a bifurcation region in the space of control parameters. This is manifested in the possibility of an abrupt change in the properties of the waveguide at the boundaries of this region and the transition of the HTSC waveguide to a strongly dissipative state. The qualitative correspondence of the properties of the generalized phenomenological model to the data of experimental studies of the HTSC coplanar waveguide is obtained.
Magnetic flux avalanches in Nb/NbN thin films
Authors: Pinheiro L. B. L. G. , Caputo M. , Cirillo C. , Attanasio C. , Johansen T. H. , Ortiz W. A. , Silhanek A. V. , Motta M.
Published: April 2020

Technological applications of NbN thin films may be threatened by the development of magnetic flux avalanches of thermomagnetic origin appearing in a large portion of the superconducting phase. In this work, we describe an approach to substantially suppress the magnetic flux avalanche regime, without compromising the upper critical field. This procedure consists of depositing a thin Nb layer before the reactive deposition of NbN, thus forming a bi-layered system. We use ac susceptibility and dc magnetometry to characterize both the single-layer films, Nb and NbN, and the bi-layered specimen, as well as calibrated magneto-optical imaging to map the instability regime of the studied samples. Magnetic flux imaging reveals interesting features of the dendritic flux avalanches in the bi-layer system, including halo-like patterns and crossing avalanches.
Break-junction tunneling spectra of Bi2212 superconducting ceramics: Influence of inhomogeneous d-wave-Cooper-pairing and charge-density-wave order parameters
Authors: Ekino Toshikazu , Gabovich Alexander M. , Li Mai Suan , Szymczak Henryk , Voitenko Alexander I.
Published: April 2020

Conductance-voltage characteristics (CVCs) of tunnel break junctions made of Bi2Sr2CaCu2O8+δ crystals were measured. It was demonstrated that the CVCs have a V-shaped inner gap region, similar to those typical of CVCs for tunnel junctions between d-wave superconductors. The CVCs have different forms for different junctions, but all of them reveal weak dip-hump structures outside the inner gap region. Calculations of the tunnel current in the ab plane of the break junctions were carried out in the model of the inhomogeneous d-wave superconductor partially gapped by charge density waves (CDWs). The averaging of the tunnel current over the statistical distributions of both the superconducting and CDW order parameters was carried out. The theoretical results qualitatively reproduce the behavior of experimental curves. A conclusion was made that tunnel directionality and the statistical distributions of both order parameters are crucial factors governing the observed CVC shapes for break junctions made of high-Tc oxides.
Threshold resonances and virtual levels in the spectrum of cylindrical and periodic waveguides
Authors: Nazarov S. A.
Published: April 2020

We describe and classify the thresholds of the continuous spectrum and the resulting resonances for general formally self-adjoint elliptic systems of second-order differential equations with Dirichlet or Neumann boundary conditions in domains with cylindrical and periodic outlets to infinity (in waveguides). These resonances arise because there are “almost standing” waves, that is, non-trivial solutions of the homogeneous problem which do not transmit energy. We consider quantum, acoustic, and elastic waveguides as examples. Our main focus is on degenerate thresholds which are characterized by the presence of standing waves with polynomial growth at infinity and produce effects lacking for ordinary thresholds. In particular, we describe the effect of lifting an eigenvalue from the degenerate zero threshold of the spectrum. This effect occurs for elastic waveguides of a vector nature and is absent from the scalar problems for cylindrical acoustic and quantum waveguides. Using the technique of self-adjoint extensions of differential operators in weighted spaces, we interpret the almost standing waves as eigenvectors of certain operators and the threshold as the corresponding eigenvalue. Here the threshold eigenvalues and the corresponding vector-valued functions not decaying at infinity can be obtained by approaching the threshold (the virtual level) either from below or from above. Hence their properties differ essentially from the customary ones. We state some open problems.
Bogolyubov’s theorem for a controlled system related to a variational inequality
Authors: Tolstonogov A. A.
Published: April 2020

We consider the problem of minimizing an integral functional on the solutions of a controlled system described by a non-linear differential equation in a separable Banach space and a variational inequality. The variational inequality determines a hysteresis operator whose input is a trajectory of the controlled system and whose output occurs in the right-hand side of the differential equation, in the constraint on the control, and in the functional to be minimized. The constraint on the control is a multivalued map with closed non-convex values and the integrand is a non-convex function of the control. Along with the original problem, we consider the problem of minimizing the integral functional with integrand convexified with respect to the control, on the solutions of the controlled system with convexified constraints on the control (the relaxed problem).

By a solution of the controlled system we mean a triple: the output of the hysteresis operator, the trajectory, and the control. We establish a relation between the minimization problem and the relaxed problem. This relation is an analogue of Bogolyubov’s classical theorem in the calculus of variations. We also study the relation between the solutions of the original controlled system and those of the system with convexified constraints on the control. This relation is usually referred to as relaxation. For a finite-dimensional space we prove the existence of an optimal solution in the relaxed optimization problem.
Geometric estimates of solutions of quasilinear elliptic inequalities
Authors: Kon’kov A. A.
Published: April 2020

Suppose that

and

are real numbers with

. Let

be a non-empty open subset of

,

. We consider the inequality

where

is the gradient operator,

and

are certain functions and

for almost all

and all

. We obtain estimates for solutions of this inequality using the geometry of

. In particular, these estimates yield regularity conditions for boundary points.
In search of infinite-dimensional Kähler geometry
Authors: Sergeev A. G.
Published: April 2020

This paper is devoted to a survey of recent results in the Kähler geometry of infinite-dimensional Kähler manifolds. Three particular classes of such manifolds are investigated: the loop spaces of compact Lie groups, Hilbert–Schmidt Grassmannians, and the universal Teichmüller space. These investigations have been prompted both by requirements in Kähler geometry itself and by connections with string theory, which are considered in the last section.

Bibliography: 43 titles.
Experimental melting curve of zirconium metal to 37 GPa
Authors: Pigott Jeffrey S , Velisavljevic Nenad , Moss Eric K , Draganic Nikola , Jacobsen Matthew K , Meng Yue , Hrubiak Rostislav , Sturtevant Blake T
Published: April 2020

In this report, we present results of high-pressure experiments probing the melt line of zirconium (Zr) up to 37 GPa. This investigation has determined that temperature versus laser power curves provide an accurate method to determine melt temperatures. When this information is combined with the onset of diffuse scattering, which is associated with the melt process, we demonstrate the ability to accurately determine the melt boundary. This presents a reliable method for rapid determination of melt boundary and agrees well with other established techniques for such measurements, as reported in previous works on Zr.
Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
Authors: Andersson Eric , Arpaia Riccardo , Trabaldo Edoardo , Bauch Thilo , Lombardi Floriana
Published: April 2020

We present the fabrication and electrical transport characterization of underdoped YBa2Cu3O7-δ nanowires. The nanowires have been realized without any protective capping layer and they show transport properties similar to those of the parent thin film, demonstrating that they have not been damaged by the nanopatterning. The current-voltage characteristics of the underdoped nanowires show large hysteretic voltage switching at the critical current, in contrast to the flux-flow like characteristics of optimally doped nanostructures, indicating the formation of a self-stabilizing hot spot. These results open up new possibilities for using the underdoped nanowires as single photon detectors and for exploring the underdoped side of the YBa2Cu3O7-δ phase diagram at the nanoscale.
Preparation of inverse photonic crystals by ETPTA photopolymerization method and their optical properties
Authors: Ashurov M S , Bakhia T , Saidzhonov B M , Klimonsky S O
Published: April 2020

Inverse photonic crystal films were prepared by photopolymerization of ethoxylate trimethylolpropane triacrylate (ETPTA) using opal-type templates. Their high quality was proved by investigations of structural and optical properties. The unexpectedly high refractive index, nETPTA ≈ 1.67, of polymerized ETPTA was obtained from a numerical approximation of the spectral positions of the reflectance peak of the films at different incidence angles. Fabricated samples were tested as sensors for water-ethanol mixtures, and a monotonous increase in the stop band shift with an increase in ethanol concentration was established.
Magnetic field driven light control by hybrid magneto-optical metasurfaces
Authors: Barsukova Maria G , Musorin Alexander I , Shorokhov Alexander S , Fedyanin Andrey A
Published: April 2020

Demonstration of magneto-optical effects enhancement in hybrid Ni/Si metasurfaces is reported. Our results show that the polarization plane rotation angle reaches the considerable value with a change of a sign in a very narrow spectral range in the vicinity of the optical magnetic dipole Mie - type resonance. The specific Faraday rotation is 160 degrees/μm, which is an outstanding effect for an ultra-thin magnetic material with a thickness of only 5 nm as used in this work. These results could be used for the creation of active nonreciprocal photonic nanostructures and metasurfaces.
Optically-driven Rotation of Perfectly Absorbing Nanoparticles
Authors: Canós Valero A. , Shalin A.S.
Published: April 2020

Optical manipulation of small scatterers assisted with auxiliary nanostructures is a very promising and already proven concept. In this work, we investigate an interesting application of angular momentum transfer in light scattering by dielectric nanoparticles. We show that, when illuminated by a circularly polarized plane wave, the scattered Poynting vector from a homogeneous dielectric cube presents a divergence-free component. Such Poynting vector distribution induces rotational motion via angular momentum transfer to any strong absorbing particle in the vicinity of the scatterer. We illustrate this effect in the case perfectly absorbing dipolar nanoparticles. The proposed design is the first step towards an efficient all-dielectric mixing scheme for micro-fluidics applications.
Ab-initio calculation of electronic properties of all-inorganic Pb-based mixed-halide perovskites
Authors: Cherotchenko E. D. , Liashenko T. G. , Agapev K. B. , Vrubel I. I. , Polozkov R. G. , Shelykh Ivan A.
Published: April 2020

Mixed lead-halide perovskite films have recently become a subject of intensive study in the nanophotonic community due to their unique optical properties. In this work we present theoretical investigations of the electronic band structure of full inorganic mixed-halide perovskites in a continuous range of chemical compositions. We demonstrate that in the orthorhombic geometry independently on the particular halogen concentrations the optical band gap remains direct, varying in the absolute value, with the fundamental absorption edge corresponding to the high symmetry point Γ of the band structure. This tunability of the optical band gap in inorganic mixed-halide perovskites is highly promising and has various possible nanophotonic and photovoltaic applications.
Modal analysis of Mie resonators: Pole-expansion of scattering operators
Authors: Colom Rémi , Mcphedran Ross , Stout Brian , Bonod Nicolas
Published: April 2020

Most of the resonant photonic structures behave like open cavities for light where light is trapped for some time before leaking or being absorbed. Their modes are called quasi-normal modes and are associated with complex eigenfrequencies

ω
n

=

ω
n
′

+
i

ω
n
″

,

ω
n
″

characterizing the rate at which the energy leaks from the structure. As a consequence, one can show that the fields of these modes diverge far away from the scatterer. This is problematic when one attempts to develop a theoretical description of the resonant interaction between light and resonant photonic stuctures in terms of their quasi-normal modes. Moreover, the existence or not of a non-resonant term in addition to these resonant contributions is still an open problem. Here, we address these two problems by deriving pole-expansions of the scattering operators of resonant optical structures. We evince the existence of a non-resonant term and we solve the problem of the divergence by studying the scattered field in the time domain and by using the causality principle. The quasi-normal mode expansion that we obtain will be of a great use to study light-matter interactions since it allows to determine the optical response of a photonic resonator both in the time and frequency domain.
Metasurfaces homogenization technique based on the computation of the average value of the contravariant tensors elements
Authors: Edee Kofi
Published: April 2020

The purpose of this paper is to present a 2D metasurfaces homogenization based on the computation of the average value of the contravariant tensors elements. A simple semi-analytical model for the comprehension of the extraordinary optical transmission (EOT) through a 2D array of periodic subwavelength metasurface is analyzed through the proposed method. In this single mode model, the mono layer of the metasurface film is considered as homogeneous medium. Therefore, the electromagnetic response of this structure to a plane wave excitation is equivalent to that of a slab with homogeneous equivalent properties. In a coordinates system where the coordinate curves xj
coincide with the physical discontinuity of the material, the covariant formalism involving contravariant components of density flux and covariant components of the electromagnetic field, allows to efficiently handle the continuity properties of the electromagnetic field. By averaging all these quantities involving local fields over the periods of the unit cell, and assuming that, these macroscopic fields and densities satisfy a constitutive relationship, the electromagnetic parameters such as averaged permittivity and permeability can be defined.
Wave transmission through a layered piezoelectric/elastic phononic crystal with capacitors
Authors: Fomenko Sergey I. , Golub Mikhail V. , Zhang Chuanzeng
Published: April 2020

In this study, elastic wave propagation through a layered phononic crystal made of finite number of unit-cells composed of four elastic/piezoelectric layers and surface electrodes connected by an electrical circuit with a capacitor is considered. The numerical investigation based on the transfer matrix method of the influence of the condenser capacitance on the stop-bands is provided. Some critical values of capacitance providing stop-band transformation into pass-bands are revealed.
Synthesis of nanocrystalline bismuth ferrite by cation-exchange method
Authors: Kalganov Dmitry A , Gryaznova Mariya S. , Bychkov Igor V , Belaya Elena A.
Published: April 2020

In the present work, cation-exchange synthesis on a previously synthesized organic matrix was used to obtain nanodispersed bismuth ferrite powder. The phase composition of the samples was investigated by X-ray diffraction. Using scanning electron microscopy images of powder particles were obtained, their morphology and size were studied. The ferromagnetic resonance in millimeter microwave frequencies at room temperature for multiferroic BiFeO3 nanopowder sample with an appropriate sample-thickness about 1 mm. was observed.
Optical binding near hyperbolic metamaterial substrates
Authors: Kostina N A , Kislov D A , Ginzburg P , Shalin A S
Published: April 2020

We study optical binding of two dielectric nanoparticles near a boundary between air and hyperbolic metamaterial. Three kinds of modes contribution are analyzed and it is shown, that evanescent waves allow formation of stable bound dimer due to hyperbolic metamaterial modes. We have found the most profitable parameters of hyperbolic metamaterial substrate, providing enhancement of the optical binding effect.
Control of the RF magnetic field pattern by tunable metasurface in 1.5 T MRI
Authors: Kretov E. , Shchelokova A. , Slobozhanyuk A.
Published: April 2020

A metasurface with a unit cell in the form of a half-wave dipole can be used as a base for the creation of wireless coils for magnetic resonance imaging (MRI). In a real structure based on a metasurface concept, the number of elements is always limited. Therefore, some elements at the edges become weaker coupled and radiofrequency (RF) magnetic field pattern becomes distorted. In this paper, we investigate metasurface-based structure with added non-uniform electrical capacitance at the ends of the resonant unit cells. We show that such a structure can be easily adjusted to work within the frequency range of the clinical 1.5 T MRI machine. Also, we demonstrate that by adding of non-uniform edge capacitances at the resonant elements, it is possible to control the RF magnetic field pattern above the structure.
High order discontinuous Galerkin methods for time-domain and frequency-domain nanophotonics
Authors: Chaumont-Frelet T. , Descombes S. , Gobé A. , Moghtader Mostafa Javadzadeh , Lanteri S. , Scheid C. , Schmitt N. , Viquerat J.
Published: April 2020

The discontinuous Galerkin (DG) method is a general numerical modeling approach that has been extensively studied in the last 20 years for the solution of many systems of partial differential equations in physics. Its development for the numerical treatment of the system of Maxwell equations was initiated by the applied mathematics community in the early 2000s. It is now a very popular method for time-domain electromagnetics, which is increasingly used and further developed by the applied physics and electrical engineering communities. More recently, a specific variant of DG, referred to as hybridized DG (or HDG), has been proposed for frequency-domain electromagnetics. DG methods possess nice features that make them particularly attractive for dealing with heterogeneous media and irregularly shaped or curved geometries, and more generally with multiscale problems. Not surprisingly, the method has also been adopted by researchers in the nano-optics field. In this paper, we report on our recent efforts for extending the capabilities of this family of methods for the numerical modeling of nanoscale light-matter interactions.
Acousto-optical deflector for non-mechanical manipulating using optical tweezers
Authors: Machikhin A S , Pichugina Y V , Kozlov A B , Batshev V I , Pozhar V E , Nosov P A
Published: April 2020

Optical tweezers are widely used in various fields of science and technology, such as biophysics, cytology and solid-state physics. Most of the existing optical tweezers use mirror or mirror-lens systems to manipulate the position of the trap. Such systems require precise alignment and do not allow the trap to be moved quickly from one arbitrary point to another due to the inertia of the mirror and lenses. We discuss acousto-optic scanning characterized by high precision and repetition rate for manipulating micro-objects using optical tweezers. Bragg diffraction of light via ultrasonic waves allows creating robust solid-state devices for precise and fast laser beam deflection. We describe a scheme of the optical tweezers with PC-driven two-dimensional scanning implemented by two sequential acousto-optical cells.
Light induced heating of silicon nanoparticles inside cervical carcinoma cells (HeLa)
Authors: Shiker A Y , Melchakova I V , Petrova M I , Makarova E K , Zyuzin M V , Milichko V A
Published: April 2020

All-dielectric nanoparticles have been recently emerged as unique components for biophotonics and drug delivery due to their resonant interaction with light providing the Raman thermometry and optical field enhancement. Here we report on the light induced heating the optically resonant silicon nanoparticles (Si NPs) up to 450 K, which were used to modify organic polymer based microcontainers. Moreover Si NPs were successfully employed for the imaging of intracellular compartments HeLa cells. The results will facilitate biocompatible usage of all-dielectric nanoparticles in medicine.
Origin of PL emission at 0.797 eV in near stoichiometric spray deposited CZTS thin films
Authors: Poornima N. , Rajeshmon V.G. , Sudha Kartha C. , Vijayakumar K.P.
Published: April 2020

Photoluminescence (PL) spectroscopy has been employed for analyzing defect levels in near stoichiometric Cu2ZnSnS4 (CZTS) thin films deposited using chemical spray pyrolysis (CSP) technique. An emission at 0.797 eV could be recorded at 15 K from the near stoichiometric CZTS thin films. This emission was persistent up to room temperature and could be identified as “donor to acceptor pair (DAP)” transition and also bears close connection with concentration of copper. Using temperature as well as excitation power dependent PL measurements and X-ray photoelectron spectroscopy (XPS) depth profile analysis, the emission at 0.797 eV could be identified as arising from transition between donor level (due to OSn defect) and acceptor level (created by Cuzn defect).
Analysis of resonance characteristics of surface plasmon-polariton modes at water-metal interfaces by Fano approximation
Authors: Nesterenko D. V. , Pavelkin R.A. , Hayashi S. , Soifer V.A.
Published: April 2020

We estimate the resonance properties of SPP modes excited at water-metal interfaces using Fano approximations in the ultraviolet, visible and infrared regions. The results obtained by Fano approximation correspond to the exact estimations and suggest more simple approach to analysis and design of resonance structures.
Time-resolved non-linear optical response and photo-induced carriers trapping in glassy semiconductors
Authors: Romanova E , Afanasiev A , Velmuzhov A , Sukhanov M , Kuzyutkina Yu , Nezdanov A , Shiryaev V
Published: April 2020

Two realisations of the pump-probe method have been used to study the time-resolved non-linear optical response of glassy chalcogenides at frequencies near their single-photon and two-photon bandgaps. Photo-excitation of gap states has been revealed as a determining effect for structural, electronic, thermal and optical changes in a glass sample.
The Methodology for Accessing the Accuracy of Apparent Diffusion Coefficient Determining
Authors: Sergunova K A , Akhmad E S , Semenov D S , Petraikin A V , Vasilev Yu A , Kivasev S A , Potrahov N N
Published: April 2020

One of the criteria for MRI neoplasms assessing is the apparent diffusion coefficient, which is calculated from the diffusion-weighted images. It is a measured parameter and is characterized by some error. A phantom including substances with self-diffusion limited to varying degrees was developed for quality assurance of diffusion-weighted images. The purpose of this work was to develop a methodology for determining the accuracy of methods and controls. The work included identification of errors sources and evaluation of each of them according to the results of numerical and phantom experiments. The method of MR-spectrometry has been used to evaluate the systematic error caused by the phantom control substances. The result of the evaluation of the phantom scan is an estimate of the magnitude of the random error determined by the operation of the tomograph. In addition, the effect of temperature variations on the measurements was evaluated. 11 experiments on tomographs of 5 different manufacturers were conducted. The accuracy of determining the apparent diffusion coefficient by each of them, as well as the comparison of the devices among themselves, showed a 16% variation.
DFT calculation of electric field effect on the energy profile of the CO oxidation reaction catalyzed by Ni nanoparticles
Authors: Serov Y M , Nestoklon M O , Gurevich S A
Published: April 2020

The DFT calculations of energy profiles for the carbon monoxide oxidation reaction in the presence of Ni catalyst in the various electric fields were performed by means of the Gaussian package. In order to do that the simple computational model was suggested for the active sites on the surface of the Ni catalyst prepared by the laser electrodispersion (LED) method. The data obtained demonstrate that the energy barriers on the reaction path, which the reaction kinetics is determined by, may be reducted in the electric field by factor from 12% up to 90%. This result supports the hypothesis, that the spontaneous charge redistribution in the catalytic systems produced by the LED method may affect significantly their catalytic activity.
Evolution of femtosecond laser-induced periodic structures formed on amorphous silicon surface
Authors: Shuleiko D V , Martyshov M N , Presnov D E , Zabotnov S V , Kashkarov P K
Published: April 2020

The laser-induced periodic surface structures (LIPSS) with period close to the femtosecond laser radiation wavelength (1.25 μm) were formed on amorphous hydrogenated silicon films (a-Si:H). The ripple ridges direction relative to laser radiation polarization was changed from perpendicular to parallel with increasing number of pulses from 50 to 1000. The experimentally observed LIPSS evolution is in a good agreement with the model proposed by J.E. Sipe where so-called efficacy factor depends on the real and imaginary parts of the dielectric constant and defines the LIPSS wave vector on the irradiated surface. In turn, the dielectric constant complex value is varied due to concentration change for the nonequilibrium electrons excited by different number of high-power femtosecond laser pulses. According to the theoretical modelling, the excited nonequilibrium electron concentration required for turning the LIPSS direction is equal to 8.2·1021 cm−3.
Strong negative longitudinal component of the Poynting vector in a tightly focused cylindrical vector beam
Authors: Stafeev S.S. , Nalimov A.G. , Kotlyar V.V.
Published: April 2020

It was shown that tightly focused cylindrical vector beam of m-th order produces reverse energy flow in the focal plane (m=2). If m=3 the reverse energy flow on the axis is equal to zero and near the axis it increases in proportion to a square of the distance to the axis. The azimuthally polarized beam of the m-th order is an example of a polarization vortex. Previously, the reverse energy flow in the focus was obtained only for vortex beams with a topological charge m and circular polarization. Numerically, using the FDTD method and the Richards-Wolf formulae, it was shown that in the focus of the zone plate such laser beams produce regions the Poynting vector opposite to the direction of propagation of the beam.