bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyperspectral regression lossless compression algorithm of aerospace images
Authors: Sarinova Assiya , Zamyatin Alexander
Published: February 2020

In this work, we propose an algorithm for compressing lossless hyperspectral aerospace images, which is characterized by the use of a channel-difference linear regression transformation, which significantly reduces the range of data changes and increases the degree of compression. The main idea of the proposed conversion is to form a set of pairs of correlated channels with the subsequent creation of the transformed blocks without losses using regression analysis. This analysis allows you to reduce the size of the channels of the aerospace image and convert them before compression. The transformation of the regressed channel is performed on the values of the constructed regression equation model. An important step is coding with the adapted Huffman algorithm. The obtained comparison results of the converted hyperspectral AI suggest the effectiveness of the stages of regression conversion and multi-threaded processing, showing good results in the calculation of compression algorithms.
Application of two-dimensional fast Fourier transform algorithm, analog of the Cooley-Tukey algorithm, for 4k fixed format digital image of satellite data in frequency domain processing
Authors: Noskov Mikhail , Tutatchikov Valeriy
Published: February 2020

Currently, digital images in the format Full HD (1920 * 1080 pixels) and 4K (4096 * 3072) are widespread. This article will consider the option of processing a similar image in the frequency domain. As an example, take a snapshot of the earth's surface. The discrete Fourier transform will be computed using a two-dimensional analogue of the Cooley-Tukey algorithm and in a standard way by rows and columns. Let us compare the required number of operations and the results of a numerical experiment. Consider the examples of image filtering.
On the issue of fluctuations in the extreme maximum runoff under the conditions of the expected climate change in the Marmarik river basin
Authors: Margaryan Varduhi , Fedotova Elena
Published: February 2020

The paper analyzes the peculiarities of formation of the absolute maximum runoff of the Marmarik river evaluates the patterns of multi-year fluctuations of maximum runoff rates in different river sites and gives a forecast of the maximum runoff in the context of global climate change. Absolute values of the maximum river runoff for different scenarios of climate change are estimated. The actual observational data of Armhydromet for maximum runoff rate, the air temperature and precipitation were used as the source material. As a result of the study, it turned out that there is only a tendency to decrease in the values of maximum runoff. It turned out that for all scenarios and cases in the Marmarik river basin, a different degree of changes in the maximum flow is observed. Moreover, the largest decrease in the maximum runoff of the Marmarik river basin is expected under the conditions of an increase in the average air temperature of the spring season by 2,7—3,9 degrees Celsius and a decrease in the amount of spring atmospheric precipitation by 2,4—2,6 %.
Anthropogenic impact on the air environment condition of megalopolis and suburban areas of forestland
Authors: Rogov Vadim , Kravchenko Nataliya , Bagaeva Oksana , Guseva Anastasiya , Sugak Evgenii
Published: February 2020

The anthropogenic impact of the megalopolis on the release of volatile matters by woody plants, air ionization in the suburban areas of the forestland for the period 1998 - 2018 was monitored. A decrease in the emission of volatile matters by woody plants, negative ions, an increase in positive ions was revealed. The composition of the air environment of a megalopolis for a long time was studied. It has been established that anthropogenic factors (dust content, gas contamination, electromagnetic radiation) increase the amount of positive ions by order of magnitude. It was revealed that the presence of electromagnetic radiation significantly affects the physical properties of air. The effect of ionization and volatile matters on the deposition rate of suspended particles was determined in laboratory conditions. Theoretical studies have been carried out, on the basis of which deterministic, differential equations of the effect of ionization on dust content, gas contamination of the air environment and the interaction of air ionization with polydisperse dust, volatile substances to produce adsorbate and its deposition rate have been obtained. The data of experimental and theoretical studies made it possible to develop measures to reduce anthropogenic environmental factors, which will improve the ecological situation and reduce the incidence of megalopolis residents.
Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates
Authors: Leon Cyril , Le Gall Sylvain , Gueunier-Farret Marie-Estelle , Kleider Jean-Paul , Roca i Cabarrocas Pere
Published: February 2020

Epitaxial silicon layers were grown on highly doped c-Si substrates using the plasma-enhanced chemical vapour deposition process (PECVD) at low temperature (175 °C). The transport and defect-related properties of these epi-Si layers were characterized by current density-voltage (J–V) and capacitance–voltage (C–V) techniques. The results show that the epi-Si layers exhibit a non-intentional n-type doping with a low apparent doping density of about 2 × 1015 cm−3. The admittance spectroscopy technique is used to investigate the presence of deep-level defects in the structure. An energy level at 0.2 eV below the conduction band has been found with a density in the range of 1015 cm−3 which may explain the observed apparent doping profile.
Effect of Inclination and of Darcy Number on Bifurcations and Thermal Transfer in a Square Porous Cavity
Authors: Aklouche-Benouaguef Sabiha , Adjal Saad , Zeghmati Belkacem.
Published: February 2020

In the present work a numerical study of natural convection in air in a square cavity filled with a porous media, was carried out in order to analyze the effects of the inclination angle and the Darcy number on the roads toward the chaos. The horizontal wall of the cavity is adiabatic while the vertical walls, composed of two part of the same size, are maintained at different temperatures. The dimensionless transfer equations, expressed in terms of stream function and vorticity had been solved using the Alternating Direction Implicit Method (ADI) and the GAUSS elimination method. The different bifurcations had been represented by attractor in phase space and by amplitude spectrum. We have noticed that for an inclination angle equal to 30°, the scenario of the roads towards the chaos is in agreement with the one of Feigen Baum. For the inclination angle equal to 60°, the scenario is that of Ruelle and Takens which is by quasi periodicity.
Hydromagnetic natural convection from a horizontal porous annulus with heat generation or absorption
Authors: Belabid Jabrane , Belhouideg Soufiane
Published: February 2020

The problem of unsteady laminar, two-dimensional hydromagnetic natural convection heat transfer in a concentric horizontal cylindrical annulus filled with a fluid-saturated porous medium in the presence of a transverse magnetic field and fluid heal generation effects is studied numerically. It is assumed that the inner and outer walls of the cylindrical annulus are maintained at uniform and constant temperatures Ti and To respectively. The model consists of the heat equation and the equations of motion under the Darcy law. The derived problem with the stream function-temperature formulation is solved numerically using the alternating direction implicit method. This investigation concerns the effect of magnetic field inclination angle, Hartmann number and heat generation on the heat transfer and the flow pattern. The obtained numerical results are presented graphically in terms of streamlines and isotherms. It was found that the heat transfer mechanisms and the flow characteristics depend strongly on the magnetic field inclination angle, Hartmann number and heat generation..
Hygrothermal behaviour of flax shives used as insulation material in an attic of a traditional house
Authors: Brachelet Franck , Asli Mounir , Antczak Emmanuel , Brue Flore , Defer Didier , Lucas Alain
Published: February 2020

Western Europe area is one of the world regions where traditionally flax is grown. Whether in France or Belgium, flax is mainly used for the production of fabrics. When separating the different components of the plant, small woody elements called shives which represented about 50% of the production, are recovered. This work aims to study the behavior of flax shives used as insulation material in an attic of a French Flanders traditional house. Main scientific issues related to the study of heat and mass transfer is to determine the evolution of the thermal characteristics of the material and its durability. First, we propose a laboratory analysis of the hygrothermal behavior of shives by conventional thermal methods for characterizing thermal conductivity and volumetric heat (heat flux method), sorption curve is also determined. Then we focus on an experimental site which is an independent house where the old insulation of the attic in glass wool was replaced by flax shives. The hygrothermal behavior of this new insulation was monitored with humidity and temperature sensors for ten months. The thermal performances determined for a raw form of the shives in the laboratory are encouraging and hygrometric results show advantageous behavior whatever the season.
Influence of Thermal Insulation’s and Phase Change Material’s Insertion within a Partition Wall on the Energy Consumption of a Conditioned Room under Adjacent Local Periodical Temperature Effect
Authors: Hanchi Nisrine , Hamza Hamid , Idmoussa Rabiaa , Lahjomri Jawad , Oubarra Abdelaziz
Published: February 2020

The aim of this work is to study the combined insertion effect of Phase Change Materials (PCM) and thermal insulation within a partition wall separating a conditioned room from an adjacent local which is under a periodic thermal activity. This is done by a comparative study with a reference wall under the same thermal conditions. The comparison criterion is the energy density transmitted to the local conditioned in established regime. The results show that the inclusion of thermal insulation and phase change material provides a significant reduction of energy consumption of the conditioned local; thereby a judicious choice of phase change material with thermal level and range melting temperature reduces further this reduction.
Transient Numerical Analysis of Free Convection in Cylindrical Enclosure
Authors: Medebber Mohamed Amine , Retiel Nourddine , Ould said belkacem , Aissa Abderrahmane , El Ganaoui Mohammed
Published: February 2020

A transient two dimensional study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103to 106and height ratios 0.5. The influence of physical and geometrical parameters on the isotherms, velocity fields, average Nusselt has been numerically investigated.
Investigation Of The Improvement Building Envelope Impact On Energy Consumption Using Energy Audit
Authors: Mokhtari Fatiha , Semmar Djaffar , Chikhi Mourad , Kasbadji Merzouk Nachida , Oukaci Soumia
Published: February 2020

Effective evaluation on the thermal performance of building envelope plays an important role towards the reduction of energy consumption for space cooling and heating. In order to estimate the energy consumption for cooling, heating and the whole energy saving on the envelop designs; an improvements of thermal performances of this envelope are introduced. This trend is performed using a numerical study. The building is an office part of the Unit of Developmental for Solar Equipment (UDES) located at Bou-Ismail, an Algerian coastal city. Through the software PLEADES-COMFIE, building energy has been evaluated. The simulation results illustrate that; adding 90 mm thick insulation on the opaque walls and double glazing on windows produce a maximum saving of 50% and 10% annual energy required in heating and cooling. Also these proposed performances allow increasing indoor temperate of 4°C in winter season and decreasing.
Numerical simulation of the flow over a tubercled wing
Authors: Baghdad Mohammed , Nehmar Abdelkader , Ouadha Ahmed
Published: February 2020

The objective of the present study is to carry out a numerical study of the flow around a NACA0021 modified wing by the incorporation of sinusoidal tubercles on its leading edge at a Reynolds number equal to 225,000. The SST k-ω turbulence model is used as closure to the incompressible governing equations. Runs have been performed for several attack angles. Results show that for lower angles of attack, tubercles reduce the drag coefficient with a slight increase in lift.
Protective Plasma Sprayed Coating forThermo-Sensitive Substrates
Authors: Oukach Soufiane , Hamdi Hassan , El Ganaoui Mohammed , Pateyron Bernard
Published: February 2020

Plasma spray is one of the surface treatment techniques that consist on the deposition of a thin coating onto a targeted substrate. Coating is built up by successive accumulation of layered splats resulting from impact and solidification of molten particles into thin ‘‘splats’’ onto the substrate. The process of droplet impact, spreading and solidification is then a crucial process in coating formation. This technique may be also used for thermo-sensitive materials such as wood by applying a metallic coating for protective or decorative purposes. However, when applying a ceramic coating which provides a high protection against hot temperatures like fire, wood may be damaged because of the high temperature at which the ceramic molten particles arrive at the substrate. In this paper, a numerical simulation based on the Finite Elements Method is carried out in order to simulate the process of the first splat formation onto a wood substrate under traditional plasma spraying conditions. The computations are carried out on a fixed eulerian structured mesh using the level set method to track the interface between the molten particle and surrounding gas. The effects of operating conditions as well as the droplet characteristics that allow applying ceramic coating onto a wood substrate without any damage to this thermo-sensitive material are investigated.
Numerical Study of Heat and Mass Transfer during the Evaporative Drying of Porous Media
Authors: SELLAMI Karima , FEDDAOUI M’barek , LABSI Nabila , OUBELLA M’hand , BENKAHLA Youb Khaled
Published: February 2020

The paper deals with numerical study of drying process of porous media of sand during the evaporation of a liquid saturated porous layer within parallel vertical channel. The liquid and air streams are modeled as two coupled laminar boundary layers incorporating non-Darcian models of the inertia and boundary effects. The governing equations and the associated boundary conditions are discretized by means of the finite volume method implemented on a staggered mesh and the velocity-pressure coupling is processed by the SIMPLER algorithm. The influences of the inlet mass flow of the drying gas, porous layer thickness and the porosity on the drying process are analyzed. Results show that the drying rate of the porous media is improved by the reduction of the porosity and porous layer thickness a large drying rate is obtained with high inlet mass flow and high inlet gas temperature.
Study of air movement and temperature distribution in a greenhouse used as a dryer
Authors: TIGAMPO Soumaïla , SAMBOU Vincent , DIEYE Younouss , TOURE Pape Moussa , BODIAN Séckou
Published: February 2020

Sun drying is the oldest way to preserve but also to valorize and store surplus agricultural production. Nowadays, several types of dryers have been developed, but the solar greenhouse dryer is an ideal solution in our tropical countries because of its implicit and higher load capacity. The greenhouse climate depends on several factors, namely the outdoor climatic conditions (air temperature, wind speed, radiation, etc.) but also on the type of materials used to cover the greenhouse. The study was carried out on a parabolic greenhouse covered by a polyethylene film with a concrete base (absorber) which in turn is placed on the ground and will be tested under the climatic conditions of Dakar, Senegal. It is in this context of sustainable development that this work is carried out. The goal is to determine the distribution of temperatures and wind speeds in the greenhouse. The simulation was carried out using the three-dimensional computer fluid dynamics software (CFD). The turbulence method (k-ε) was used and to solve the radiation transfer equation (RTE) we introduce the discrete ordered method DO. We also add the “Solar Load Model” which gives the position of the sun and its radiations in relation to the layout of the greenhouse according to the date and time of the simulation. The simulation is carried out in a closed greenhouse and the results found can be used to improve the design and control of the greenhouse climate. Air temperatures and velocities simulation give an average of 325.95 K and 0.114 m/s respectively.
Experimental analysis of a Vapour-Liquid Separated Flat Loop Heat Pipe Evaporator System
Authors: Yang Yang , Kai Zhu , Yabo Wang , Jie Wei , Chen Sarula
Published: February 2020

In this paper, a unique operation mechanism of loop heat pipe (LHP) was proposed. To test the performance of LHP under this new mechanism, a visual flat LHP evaporator prototype and an open experimental system were designed and assembled, and start-up experiment and variable heat load experiment were done respectively to obtain the actual operation characteristics, such as the evaporator thermal resistance (Re), total thermal resistance (Rt), start-up time and temperature of base plate. The proposed LHP had better overall performance during the start-up tests when He value of EC was set to 0.5mm, and its corresponding Re and Rt value were 0.035 K/W and 0.451 K/W when the heating power was 208w. Meanwhile, as per the heat load applied to the base plate, the whole variable heat load experiment could be divided into three distinct stages: low heat load stage, efficiency operation stage and dry-out stage. Moreover, the results also showed that the circulation driven head formed inside of the EC played an important role in promoting the operation performance, especially when the wick, the vapour-liquid interface and the bottom of the evaporator arrived at a reasonable situation.
Thermal behavior of ceramic particles in a gaseous medium at high temperature
Authors: AISSA Abderrahmane , ZAIM Abdel-Nour , SAHNOUN M , FARES Redouane , ABDELOUHAB M , EL GANAOUI Mohammed
Published: February 2020

Numerical simulation of the interaction between the spherical particle and plasma gas is carried out. The aim of this study is to investigatethermal transfer between the plasma gas and solid particle during the plasma spray process and to validate the well-known empirical correlation of the Ranz and Marshall. In the conditions of molten or semi-molten states of prepared substrate, the medium (plasma jet) can affect the high velocities of particles. On the basis of direct numerical simulation, the computational analysis has been carried out by using computational fluid dynamics (CFD) of heat transfer in atmospheric pressure and mid-temperature range (3000k–12000k) of a plasma flow over a spherical particle. Our proposed model improves correlation with experiments compared to the existing approaches in the literature.
Schlechte Luft durch Verkehr, Industrie und Landwirtschaft
Authors: Lelieveld Jos
Published: February 2020

Die Belastung der Außenluft mit Schadstoffen, insbesondere Feinstaub, ist einer der 5 wichtigsten Gesundheitsrisiken. Sie kann zu Lungen- und Herz-Kreislauferkrankungen sowie zum vorzeitigen Tod führen. Der durchschnittliche Verlust an Lebenserwartung durch schlechte Luft in Deutschland und den Europäischen Nachbarländern beträgt mehr als 2 Jahre. Eine wichtige Quellkategorie von Luftschadstoffen ist die Nutzung fossiler Brennstoffe durch Verkehr und Industrie. Allerdings ist die Landwirtschaft in Deutschland nahezu gleichbedeutend, da der Ausstoß von Ammoniak wesentlich zur Feinstaubbelastung beiträgt. Da die Wirkung von Ammoniak bei der Feinstaubbildung in der Atmosphäre nicht proportional mit der Konzentration abnimmt, ist es notwendig, die Ammoniakemissionen drastisch zu verringern. Studien zeigen, dass Maßnahmen hierzu technisch möglich und wirtschaftlich vorteilhaft sind. Um geringere Treibhausgas- und Luftschadstoff-Emissionen für Gesundheit, Umwelt und Klima zu erreichen, sind neue Zukunftskonzepte für eine nachhaltige Mobilität, Energieversorgung und Landwirtschaft erforderlich.
Ernährungsintervention im medizinischen Alltag
Authors: Stephanie Balz
Published: February 2020

Immer mehr Menschen in Deutschland leiden an Erkrankungen wie Adipositas oder Diabetes mellitus Typ 2, die zum großen Teil durch eine unausgewogene Ernährung ausgelöst werden. Der ernährungsmedizinischen Versorgung kommt eine immer größere Bedeutung bei der Behandlung von Krankheiten zu.
Stadtluft: „hot and dusty“
Authors: Liebers Uta , Maglakelidze Maka , Witt Christian
Published: February 2020

Die gesundheitsschädigende Wirkung von Luftschadstoffen ist durch eine Vielzahl von Studien belegt. Eine erhöhte Konzentration von Feinstaubpartikeln (PM10 und PM2.5), Ozon und Stickoxiden triggern inflammatorische Prozesse an den Schleimhäuten der Atemwege und am Endothel. Diese kann zur Progression oder Exazerbation chronischer Krankheiten führen und akute respiratorische oder kardiovaskuläre Symptome auslösen. Die Exposition gegenüber Luftschadstoffen ist konzentrationsabhängig mit einem Anstieg der Mortalität und Morbidität assoziiert. Vulnerable Gruppen sind Säuglinge und Kleinkinder, aber auch ältere Personen und polymorbide Patienten. Diese Bevölkerungsgruppen sind vor allem in Metropolenregionen nicht nur den erhöhten Luftschadstoffen, sondern im Rahmen des Klimawandels auch zunehmender Hitzebelastung ausgesetzt.

Die Stimme der Ärzte ist wichtig, um die Bevölkerung auf die gesundheitlichen Auswirkungen von Luftschadstoffen im Klimawandel hinzuweisen und fortschrittliche Lösungen zum Hitzeschutz auch in den Kliniken zu unterstützen.
Directing-Group-Assisted Transition-Metal-Catalyzed Direct C–H Oxidative Annulation of Arenes with Alkynes for Facile Construction of Various Oxygen Heterocycles
Authors: Kuang Guanghua , Liu Guangyuan , Zhang Xingxing , Lu Naihao , Peng Yiyuan , Xiao Qiang , Zhou Yirong
Published: February 2020

The most recent advances in the construction of oxygen heterocycles by the directing-group-assisted transition-metal-catalyzed direct oxidative annulation of arenes with diverse alkynes are summarized in this review. More than 140 recent research papers and many closely related reviews are referenced in this paper. Nine different oxygen heterocycles frameworks are discussed. Several traditional transition-metal catalysts as well as some classical non-noble metals are utilized to promote the annulation. Three plausible controlling models are disclosed to clarify the excellent regioselectivity outcomes achieved in case of unsymmetrical alkyne substrates.

1 Introduction

2 Coumarins

3 I socoumarins and Their Analogues

4 2-Pyrones and Their Analogues

5 Chromones and Chroman-4-ones

6 Chromenes and Isochromenes

7 Fused Polycyclic Oxygen Heteroaromatics

8 Benzofurans, Dihydrobenzofurans, and Furans

9 Phthalides and Benzofuranones

10 Benzoxepines

11 Conclusion
Candida and Oral Candidosis—A Review
Authors: Mallya Sachidananda , Mallya Shrikara
Published: February 2020

Oral candidiasis (also called candidosis) is an opportunistic infection affecting the oral mucosa. These lesions are very common and caused by yeast Candida albicans. C. albicans are normal component of oral microflora and around 30 to 50% carry these organisms. The rate of carriage increases with advancing age of the patient. C. albicans are recovered from patient’s mouth over the age of 60 years. Other species such as C. glabrata, C. tropicalis, C. guilliermondii, and C. krusei are infrequently but consistently isolated. Oral candidosis can be classified into primary and secondary candidiasis. The factors involved in the pathogenicity of C. albicans have been reviewed. The pathogenesis of different biotypes and strains of C. albicans varies. A relationship has been suggested between the adherence of C. albicans to surfaces and its ability to colonize and cause disease. An important aspect of the pathogenicity of C. albicans may be its nonspecific affinity and binding to acrylic resin and other plastics. The factors affecting adhesion of yeasts, related to yeast cells, related to host cells and environmental factors, and the main factors which increase the susceptibility of oral candidiasis have been reviewed. The different types of oral lesions, their identification by different methods, management, and treatment of oral candidiasis also have been highlighted.

Oral candidosis as a common opportunistic infection has gained importance after the discovery of human immunodeficiency virus infection. Candidiasis was always an endogenous infection. There are few cases of exogenous infection in intravenous drug abusers and contact lens users. Esophageal candidiasis is the earliest and most cases of lesions seen in acquired immunodeficiency syndrome patient. The diagnosis and reporting of oral candidiasis should be done with utmost care. The finding of yeast cells in large numbers and presence of pseudohyphae indicate invasion and causative agent of infection. The diagnosis of Candida infection can be confirmed by various techniques and recently discovered advanced methods.

The confirmation of Candida infection depends on clinical diagnosis, proper collection of specimen, and careful evaluation in methodology and reporting.
Multidetector Computed Tomography Evaluation of Omental Infarct
Authors: Babu Merin , Avantsa Rohini
Published: February 2020

Background Omental infarction is a rare cause of acute pain abdomen and is difficult to diagnose clinically due to nonspecific clinical features. Multidetector computed tomography (MDCT) imaging of the abdomen is essential for the diagnosis of omental infarction and is also crucial to rule out appendicitis and other causes of acute pain abdomen.

Objective The main purpose of this article is to describe the MDCT features of omental infarction in clinching the diagnosis and differentiating it from its clinical mimics.

Methods CT findings of five patients with diagnosed omental infarction were retrospectively reviewed from 2014 to 2019. All patients presented with pain abdomen on the right side of the abdomen with various clinical diagnoses. MDCT was done for diagnosis and features evaluated include size of the lesion, location, relation to colon, and findings that were correlated to clinical presentation and etiology.

Results Age distribution ranged between 36 and 55 years with female predominance. Out of five cases, one was secondary omental infarction due to inguinal hernia causing omental torsion and the other four cases were of unknown etiology. Three cases were managed conservatively and the other two cases were surgically managed. Three lesions were in right iliac fossa and two lesions were in the supraumbilical region on the right side.

Conclusion Omental infarction should be considered important in the differential diagnosis of acute pain abdomen mimicking acute appendicitis and requires CT abdomen to establish diagnosis. Knowledge of typical imaging findings and application for diagnosis are important, as it is a self-limiting disease and can avoid unnecessary surgical interventions.
Emerging Technologies, Market Segments, and MarkeTrak 10 Insights in Hearing Health Technology
Authors: Edwards Brent
Published: February 2020

Hearing health care is rapidly changing through innovation in technology, services, business models, and product categories. The introduction of hearables and over-the-counter (OTC) hearing aids in particular will change the market for hearing help and the role of the hearing care professionals (HCPs). This article focuses on how these products will be differentiated from HCP-fit hearing aids through their ability to address the unmet needs of different consumer segments within the population of people with hearing dysfunction. The unmet hearing needs of each segment are discussed, and the size of each segment estimated, demonstrating a large potential market for hearables and a smaller potential market for hearing aids than has been previously mentioned in the literature. The results from MarkeTrak 10's survey of consumers' attitudes toward an OTC model are reviewed, showing that approximately half of both hearing aid owners and nonowners are uncomfortable doing hearing- and hearing aid–related tasks on their own without the assistance of an HCP and would be unlikely to purchase OTC hearing aids if available today. MarkeTrak data are also shown that demonstrate that the majority of hearing aid and personal sound amplification product owners believe that the HCP helped or would have helped with their hearing devices. Finally, challenges to OTC hearing aids becoming successful are discussed.
Improved ferroelectric response of pulsed laser deposited BiFeO3-PbTiO3 thin films around morphotropic phase boundary with interfacial PbTiO3 buffer layer
Authors: Sahoo Kishor Kumar , Katoch Rajesh , Brajesh Kumar , Garg Ashish , Gupta Rajeev
Published: February 2020

(1 − x)BiFeO3-xPbTiO3 (BF-xPT) is an interesting material for sensing and actuating devices with large polarization near the morphotropic phase boundary (MPB) (x = 0.30) in the bulk form. However, pulsed laser deposition (PLD) grown (BF-xPT) thin films usually show high electrical leakage and, hence, saturated ferroelectric hysteresis loops are only obtained at subzero temperatures. In this article, we report on high room temperature ferroelectric polarization with saturated hysteresis loops in pulsed laser deposited (BF-xPT) polycrystalline thin films of compositions near the MPB with the use of a thin buffer layer of PbTiO3 (PT). The thin films possessed a perovskite structure with excellent crystallinity and exhibit the presence of a monoclinic (Cm) phase (MA-type) for x = 0.20–0.25 and a mixture of a monoclinic (Cm) phase and a tetragonal (P4mm) phase for x = 0.30–0.35 compositions. The thin films with composition x = 0.25 exhibit a monoclinic phase and yield very large room temperature ferroelectric polarization (2Pr > 80μC/cm2), perhaps the highest room temperature ferroelectric polarization and excellent piezoelectric properties in PLD deposited (BF-xPT) thin films of near-MPB composition. Furthermore, the evolution of ferroelectricity with PT content, studied using room temperature Raman spectroscopy, reveals a correlation with lattice dynamics and stereochemical activity of Bi. Piezoforce domain analysis of the thin films reveals that ferroelectric polarization and electrical leakage in the thin films are intricately related to the type of domains present in the samples, viz., 180°, 109°, 90°, and 71° due to differences in the nature of the domain walls.
Anomalous magnetorheological effect in unstructured magnetoisotropic magnetoactive elastomers
Authors: Kalita V. M. , Dzhezherya Yu. I. , Levchenko G. G.
Published: February 2020

It was found that the anomalous magnetorheological effect observed in initially unstructured magnetoisotropic magnetoactive elastomers, i.e., the growth of their effective shear modulus in an external magnetic field by almost two orders of magnitude, is a result of the uniaxial magnetic anisotropy induced by the magnetic field. An additional magnetoelastic contribution to the mechanical stress created by the induced magnetic anisotropy counteracts the shear and increases the effective shear modulus of the magnetoactive elastomer when the latter is magnetized. Numerical estimates made for the magnitude of magnetorheological effect are in good agreement with known experimental data.
Three-dimensional measurement of Mg dopant distribution and electrical activity in GaN by correlative atom probe tomography and off-axis electron holography
Authors: Amichi Lynda , Mouton Isabelle , Di Russo Enrico , Boureau Victor , Barbier Frédéric , Dussaigne Amélie , Grenier Adeline , Jouneau Pierre-Henri , Bougerol Catherine , Cooper David
Published: February 2020

The distribution and electrical activity of p-type doping (Mg) in gallium nitride (GaN) grown by metal organic chemical vapor deposition was investigated by correlating atom probe tomography (APT) and off-axis electron holography. APT results revealed that high Mg concentrations promote the formation of Mg-rich clusters. This is associated with the formation of pyramidal inversion domains (PIDs). The direct measurement of the doping concentration outside the clusters provided by APT suggests a saturation in the p-type electrical activity for Mg concentrations above 7 × 1019 cm−3. Maps of the electrostatic potential provided by off-axis electron holography confirm that the highest carrier concentration was achieved in the regions with the highest dopant concentration of 2 × 1020 cm−3, despite the presence of a high density of Mg-rich clusters revealed by APT. The correlation of these techniques suggests that PIDs are not the major cause of the reduction in electrostatic potential.
Enhanced multiferroicity in Mn- and Cu-modified 0.7BiFeO3 − 0.3(Ba0.85Ca0.15)TiO3 ceramics
Authors: Shu MingFang , Wang Dong , Li Sumei , Yin Lihua , Wang Caixia , Song Wenhai , Yang Jie , Zhu Xuebin , Sun Yuping
Published: February 2020

The effect of CuO and MnO2 as sintering additives on the structural, ferroelectric, and magnetic properties of 0.7BiFeO3−0.3(Ba0.85Ca0.15)TiO3 was investigated. The addition of CuO can inhibit grain growth, and the sample possesses the maximum remanent magnetization. However, the addition of MnO2 can promote grain growth, and the sample exhibits the maximum remanent polarization of 34μC/cm2. Nevertheless, the addition of both CuO and MnO2 can markedly enhance the magnetic properties. The magnetization measurements manifest that all the samples undergo a paramagnetic to ferrimagnetic transition arising from the existence of a net moment due to the antiferrimagnetic interactions between Fe2+ and Fe3+ sublattices. The enhanced magnetism of the samples with the addition of CuO and MnO2 can be due to the enhanced superexchange interaction between Fe2+ and Fe3+ arising from the increased Fe–O–Fe bond angle.
Electrical characterization of GaN Schottky barrier diode at cryogenic temperatures
Authors: Chen Jiaxiang , Zhu Min , Lu Xing , Zou Xinbo
Published: February 2020

In this report, electrical characteristics of the Ni/GaN Schottky barrier diode grown on sapphire have been investigated in the range of 20 K–300 K, using current–voltage, capacitance–voltage, and deep level transient spectroscopy (DLTS). A unified forward current model, namely a modified thermionic emission diffusion model, has been developed to explain the forward characteristics, especially in the regime with a large ideality factor. Three leakage current mechanisms and their applicability boundaries have been identified for various bias conditions and temperature ranges: Frenkel–Poole emission for temperatures above 110 K; variable range hopping (VRH) for 20 K–110 K, but with a reverse bias less than 20 V; high-field VRH, in a similar form of Fowler–Nordheim tunneling, for cryogenic temperatures below 110 K, and relatively large bias (>25 V). Four trap levels with their energy separations from the conduction band edge of 0.100 ± 0.030 eV, 0.300 eV, 0.311 eV, and 0.362 eV have been tagged together with their capture cross sections and trap concentrations. The significantly reduced DLTS signal at 100 K suggested that traps practically became inactive at cryogenic temperatures, thus greatly suppressing the trap-assisted carrier hopping effects.
In situ oxidation studies of Cu thin films: Growth kinetics and oxide phase evolution
Authors: Unutulmazsoy Yeliz , Cancellieri Claudia , Chiodi Mirco , Siol Sebastian , Lin Luchan , Jeurgens Lars P. H.
Published: February 2020

A comprehensive understanding of the oxidation of Cu thin films in the low-temperature regime is of fundamental interest and particularly relevant for applications in the fields of micro- and nanoelectronics, sensors, catalysis, and solar cells. The current study reports on the oxidation kinetics of PVD grown Cu thin films (20–150 nm thick) and the oxide phase evolution from Cu2O to CuO upon thermal oxidation in the temperature range of 100–450 °C. XRD investigations in the laboratory and at the synchrotron show that the oxide phase formation critically depends on the oxidation conditions such as temperature and oxygen partial pressure. The real-time synchrotron XRD measurements reveal that the formation of the CuO phase only starts after complete oxidation of the Cu films to Cu2O films. In situ resistance measurements were performed to follow the oxide growth rate of Cu2O on Cu films in the temperature range of 100–300 °C in air and in 10 mbar pO2. It is found that the oxidation kinetics of Cu films to Cu2O films follows the linear rate law, which is attributed to surface reaction controlled oxidation. The oxygen dissociation rate at the gas–solid interface is the rate-limiting process. A dramatic decrease in the linear oxidation rate is observed at low oxygen partial pressures. The fundamental differences between the oxidation rate-limiting processes of Cu as compared to other transition metal films are discussed.
Multiple-ion-ejection multi-reflection time-of-flight mass spectrometry for single-reference mass measurements with lapping ion species
Authors: Fischer Paul , Schweikhard Lutz
Published: February 2020

Repeated switching of electric potentials within a single experimental cycle is introduced for a multi-reflection time-of-flight mass spectrometer (also known as an electrostatic ion beam trap) in order to eject different ion species after different storage times. The method is demonstrated with two cluster ions with considerably different mass-to-charge ratios (the A = 624 and 832 isotopologues of Pb3+ and Pb4+, respectively) for the specific case where the sequential ejections result in an identical number of revolution periods. Thus, the ions’ flight lengths are identical, and the resulting time-of-flight values allow single-reference mass determination. The requirements for the switching time window are studied in detail. For the present system and ion pair, the relative mass uncertainty is found to be 3 · 10−7 for short measurements (≈10 min) and 6 · 10−8 for longer ones (≈2 h).
Evaluation of performance of near-field thermophotovoltaic systems based on entropy analysis
Authors: Li Bowen , Cheng Qiang , Song Jinlin , Zhou Kun , Lu Lu , Luo Zixue
Published: February 2020

Near-field radiative heat transfer can significantly improve the output power of thermophotovoltaic (TPV) systems. Therefore, it is crucial to explore how to increase the energy conversion efficiencies of near-field TPV systems. In this study, based on the fluctuation–dissipation theorem with the effective medium theory, we evaluate the performance of a near-field TPV system from the formulation of thermodynamics. It is found that a near-field TPV system consisting of InAs or GaSb cell can achieve higher heat flux or efficiency limit, respectively. Moreover, the TPV system with a hyperbolic metamaterial (HMM) emitter composed of nanowire or nanohole arrays can achieve higher heat flux and efficiency limit compared to that of the bulk reference. This is attributable to the HMMs being able to support hyperbolic modes, and the radiation with the HMM emitter exhibits a favorable entropy content for the energy conversion efficiency. This work provides an approach to determine the efficiency limit and establish a target for efficiency of the near-field TPV system without considering how the system works. The results of this study will facilitate the design and application of the HMM emitter and material of the TPV cell to improve the efficiency of near-field TPV systems.
Shape-controlling effects of hydrohalic and carboxylic acids in TiO2 nanoparticle synthesis
Authors: Sellschopp K. , Heckel W. , Gäding J. , Schröter C. J. , Hensel A. , Vossmeyer T. , Weller H. , Müller S. , Vonbun-Feldbauer G. B.
Published: February 2020

The ability to synthesize nanoparticles (NPs), here TiO2, of different shapes in a controlled and reproducible way is of high significance for a wide range of fields including catalysis and materials design. Different NP shapes exhibit variations of emerging facets, and processes such as adsorption, diffusion, and catalytic activity are, in general, facet sensitive. Therefore, NP properties, e.g., the reactivity of NPs or the stability of assembled NPs, depend on their shape. We combine computational modeling based on density functional theory with experimental techniques such as transmission electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray powder diffraction to investigate the ability of various adsorbates, including hydrohalic and carboxylic acids, to influence NP shape. This approach allows us to identify mechanisms stabilizing specific surface facets and thus to predict NP shapes using computational model systems and to experimentally characterize the synthesized NPs in detail. Shape-controlled anatase TiO2 NPs are synthesized here in agreement with the calculations in platelet and bi-pyramidal shapes by employing different precursors. The importance of the physical conditions and chemical environment during synthesis, e.g., via competitive adsorption or changes in the chemical potentials, is studied via ab initio thermodynamics, which allows us to set previous and new results in a broader context and to highlight potentials for additional synthesis routes and NP shapes.
Comparing steady state photothermalization dynamics in copper and gold nanostructures
Authors: Hogan Nicki , Sheldon Matthew
Published: February 2020

Metal nanostructures have been the focus of several recent studies due to their ability to generate high energy, non-equilibrium “hot” electrons for use in photochemical and photocatalytic applications. In particular, there is growing interest to understand how differences in the electronic structure and optical response of different metals may impact the behavior and utility of their hot electrons in chemical reactions. Using a continuous wave anti-Stokes Raman spectroscopy technique recently developed in our laboratory, in this study, we measured the temperature and lifetime of hot electrons in gold and copper nanostructures in order to understand how the choice of metal impacts hot electron dynamics during steady state illumination. We found that hot electrons in copper are more abundant and more reactive than those in gold, suggesting that copper nanostructures may be a more promising platform for performing hot electron photochemistry.
Exploiting the advantages of the centrifugal softening effect in rotational impact energy harvesting
Authors: Fang Shitong , Wang Suo , Zhou Shengxi , Yang Zhichun , Liao Wei-Hsin
Published: February 2020

This Letter presents a rotational impact energy harvester by utilizing the centrifugal softening effect of an inverted driving beam in improving the energy harvesting performance of two piezoelectric beams at low rotational frequencies. By our proposed structure, the static divergence of the inverted driving beam in the deflected mode can not only be avoided but also be utilized. Numerical and experimental results show that the centrifugal softening effect can amplify the relative motion between the driving and generating beams and increase the impact force, which in turn improves the output power significantly. The maximum output power of the harvester is increased by 212.5%, 258.7%, and 682.8% for the impact gaps of 1.07 mm, 1.43 mm, and 2.14 mm, respectively. Moreover, the inverted driving beam can be prevented from continuously deflecting by introducing large impact stiffness at the contact instant.
Optimized effective potentials to increase the accuracy of approximate proton transfer energy calculations in the excited state
Authors: Partovi–Azar Pouya , Sebastiani Daniel
Published: February 2020

Many fundamental chemical reactions are triggered by electronic excitations. Here, we propose and benchmark a novel approximate first-principles molecular dynamics simulation idea for increasing the computational efficiency of density functional theory-based calculations of the excited states. We focus on obtaining proton transfer energy at the S1 excited state through actual density functional theory calculations at the T1 state with additional optimized effective potentials. The potentials are optimized as such to reproduce the excited-state energy surface obtained using time-dependent density functional theory, but can be generalized to other more accurate quantum chemical methods. We believe that the presented method is not only suitable for studies on excited-state proton transfer and ion mobility in general systems but can also be extended to investigate more involved processes, such as photo-induced isomerization.
Beyond Marcus theory and the Landauer–Büttiker approach in molecular junctions. II. A self-consistent Born approach
Authors: Sowa Jakub K. , Lambert Neill , Seideman Tamar , Gauger Erik M.
Published: February 2020

Marcus and Landauer–Büttiker approaches to charge transport through molecular junctions describe two contrasting mechanisms of electronic conduction. In previous work, we have shown how these charge transport theories can be unified in the single-level case by incorporating lifetime broadening into the second-order quantum master equation. Here, we extend our previous treatment by incorporating lifetime broadening in the spirit of the self-consistent Born approximation. By comparing both theories to numerically converged hierarchical-equations-of-motion results, we demonstrate that our novel self-consistent approach rectifies shortcomings of our earlier framework, which are present especially in the case of relatively strong electron–vibrational coupling. We also discuss circumstances under which the theory developed here simplifies to the generalized theory developed in our earlier work. Finally, by considering the high-temperature limit of our new self-consistent treatment, we show how lifetime broadening can also be self-consistently incorporated into Marcus theory. Overall, we demonstrate that the self-consistent approach constitutes a more accurate description of molecular conduction while retaining most of the conceptual simplicity of our earlier framework.
How short is the runaway electron flow in an air electrode gap?
Authors: Mesyats G. A. , Yalandin M. I. , Zubarev N. M. , Sadykova A. G. , Sharypov K. A. , Shpak V. G. , Shunailov S. A. , Ulmaskulov M. R. , Zubareva O. V. , Kozyrev A. V. , Semeniuk N. S.
Published: February 2020

We present and analyze characteristics of the runaway electron flow in a high-voltage (the voltage rise rate of up to 1.5 MV/ns) air-filled electrode gap with a strongly nonuniform electric field. It is demonstrated that such a flow contains a high-energy electron component of duration not more than 10 ps. According to numerical simulations, runaway electron generation/termination is governed by impact ionization of the gas near the cathode and switching on/off a critical (sufficient for electrons to run away) electric field at the boundary of the expanding cathode plasma. The corresponding characteristic time estimated to be 2–3 ps is defined by the ionization rate at a critical field.