jablonkagroup/rise_ai_scientists huggingface dataset:
Authors: S. Ragini | S. Bharadwaj | Suman Kumar Burnwal | S. R. Murthy
Source: International Journal of Applied Engineering Research (article, 2018-03-30)
Field: Materials Science — Materials Chemistry

Dielectric Properties of Mixed Ferrite (Mn0.4Zn0.6Fe2O4 and Co0.4Zn0.6Fe2O4) Composites Soft ferrite (Mn0.4Zn0.6Fe2O4) and hard ferrite (Co0.4Zn0.6Fe2O4) nanocomposites (x Mn0.4Zn0.6Fe2O4 + (1-x) Co0.4Zn0.6Fe2O4 (where x= 0.25, 0.5, 0.75) were prepared with different weight percent. Crystal structures and microstructures of these composites have been investigated by using X-ray diffraction and scanning electron microscope for composite samples sintered at 900C/30 min using microwave sintering technique. The effect of composite weight percent on dielectric properties of composites are examined over a wide frequency range (1MHz-1.8GHz) by studying the real and imaginary part of permittivity with available theories. Investigation show variation of mixed ferrites for resistivity and resonating frequency. Ferrite (magnet) ; Composite material ; Materials science ; Dielectric ; Optoelectronics Magnetic Properties and Synthesis of Ferrites ; Electromagnetic wave absorption materials
Authors: Savannah D. Benusa
Source: VCU Scholars Compass (Virginia Commonwealth University) (article, 2018-01-01)
Field: Materials Science — General Materials Science

MECHANISMS REGULATING AXON INITIAL SEGMENT STABILITY Axon initial segment (AIS) disruption has been described in a number of pathological environments where neuroinflammation is a contributing factor; however, whether this disruption is reversible in unknown. To address the principle of AIS structural recovery, we employed an acute neuroinflammatory model. Acute neuroinflammation induced disruption of AIS structural and functional domains and, importantly, upon resolution of neuroinflammatory conditions, was reversed.\nConsistent with other studies, we observed a close interaction of microglia with AISs, and utilized this acute neuroinflammatory model to investigate the relationship between reactive microglia and AIS integrity. Gene expression analysis of microglial transcription profiles identified reactive oxygen species (ROS)-producing enzymes as candidates in AIS pathogenesis. Experiments employing mice lacking the major ROS-producing enzyme NOX2, identified ROS as mediators of AIS disruption. Furthermore, we established calcium-dependent protease calpain as a disruptor of AIS protein clustering in inflammation-induced disruption.\nSince we observed an intimate interaction between microglia and the AIS, we conducted studies designed to identify a candidate in microglia that regulates microglial-AIS contact. During chronic inflammatory conditions, microglia enhance contact with AISs often completely surrounding the domain. Concomitant with this morphological change, neurofascin (Nfasc) expression increased in microglia. Nfasc is a cell adhesion molecule with cell-specific isoforms known to mediate glial-neuronal interactions, but until now, was not reported to be expressed by microglia. Here, I characterize the unique Nfasc isoform expressed by microglia and present evidence that suggests that microglial Nfasc may mediate microglial-AIS contact, a potentially pivotal interaction in the induction of AIS disruption by pro-inflammatory factors. Neuroscience ; Computer science ; Biology Material Properties and Applications ; Smart Materials for Construction
Authors: Robert M. Allen
Source: SPIRE - Sciences Po Institutional REpository (preprint, 2018-07-26)
Field: Materials Science — Materials Chemistry

Exploratory simulations of multiscale effects of deformation twinning on the mechanical behavior of FCC and HCP metals Methods designed for incorporation into multiscale modeling polycrystals are presented in this work in two tasks. This work contains mesoscale methods for capturing the effects of both the interactions of slip dislocations encountering twin grain boundaries and the simultaneous growth of multiple twin grain volume fractions on mechanical hardening and texture evolution. These are implemented in a crystal plasticity framework using the Los Alamos viscoplastic self-consistent code, VPSC-7. Presented here, the effects of simultaneous growth in multiple twin variants on textural evolution is tracked using a Kalidindi-type twin volume transfer scheme. In Task 1, the implementation of this scheme in order to simulate the texture of Twinning Induced Plasticity steels (TWIP) subjected to Equal Channel Angular Pressing (ECAP) are summarized. In Task 2, the hardening effects of two types of interactions between slip dislocations and encountered twin grain boundaries, namely dislocation transmutation and dissociation, are captured by way of modifying the dislocation density based hardening model of [11]. Interactions of the first type are presented in a constitutive relation calculating the amount of dislocation density apportioned to a given slip system contained within the encountered twin volume fraction from each interacting slip system in the parent volume fraction. The amount transmuted from each interacting slip system described using the Correspondence Method, an on to mapping of slip systems in a parent grain to slip systems in considered twin grains. Interactions of the second type are then introduced into this constitutive relation as a disassociation parameter, the value of which is established by observations gleaned from the results of the molecular dynamics simulations of [8] and [53]. These methods are implanted to simulate the anisotropic hardening behavior of HCP magnesium under multiple load paths Humanities ; Twip ; Philosophy ; Materials science ; Crystal twinning ; Metallurgy Microstructure and mechanical properties ; Microstructure and Mechanical Properties of Steels ; Metallurgy and Material Forming
Authors: René Tannert | Fabian Henn | Benoit Jan Rhein | Laura Hennes | A. Berkefeld | Lorenz Ratke | Barbara Milow
Source: elib (German Aerospace Center) (article, 2018-09-24)
Field: Chemistry — Spectroscopy

Aerogel-honeycomb sandwich composites based on resorcinol-formaldehyde and silica Composites consisting of aerogels are lightweight materials with possible applications in many fields including the aerospace, automotive, and building sectors. In that context, we have previously demonstrated how aerogels derived from resorcinol-formaldehyde and silica can be mechanically reinforced using aramid-, paper-, or aluminum-based honeycomb structures as matrix in the sol-gel process. This poster describes efforts to produce sandwich materials using such honeycomb-aerogel-composites as core material, and metal sheets as coating. Qualitative studies regarding different adhesives and suitable joining methodology for aerogel-honeycomb composites, as well as joining of core composite and aluminum sheets of varying thickness are described. The resulting sandwich materials were characterized in terms of their thermal and mechanical behavior. More specifically, the thermal conductivity of sandwich materials and core components were determined using a heat flow meter or transient plane source technique, respectively. Regarding mechanical properties, compressive, tensile, shear, and bending tests were performed. The combined results allow for the design of aerogel composite sandwich materials with a balanced trade-off between thermal and mechanical properties. The studies presented herein will guide current and future efforts directed to the production of generic parts for automotive applications. Aerogel ; Materials science ; Composite material ; Sandwich-structured composite ; Composite number ; Thermal conductivity ; Honeycomb ; Nanoporous ; Adhesive ; Honeycomb structure ; Coating ; Ultimate tensile strength ; Layer (electronics) Aerogels and thermal insulation ; Surface Modification and Superhydrophobicity ; Polymer composites and self-healing
Authors: Michael W. Swift
Source: eScholarship (California Digital Library) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Electronic Structure of Materials for Novel Computing and Energy Applications First-principles calculations based on density functional theory are an invaluable tool in the prediction and understanding of materials properties based on their atomic and electronic structure. Computational results provide relevant insight for applications in the energy sector and in novel computational platforms. We begin by addressing a longstanding problem: the computation of binding energies and hyperfine interactions for shallow dopants in semiconductors. We have developed new techniques for calculating these properties with remarkable accuracy, providing guidance for engineering of spin qubits. We move on to electronic complex oxides, studying electron-electron scattering in SrTiO3. We develop a general methodology to calculate electron-electron scattering rates, and identify the conditions under which the mechanism gives rise to a well-known T2 power law in resistivity. We then turn to the unconventional electronic phase found in the spin-orbit Mott insulator Sr3Ir2O7. The electron-doping-driven metal-insulator transition is studied and structural distortions in the correlated metallic state are shown to arise from a different mechanism from the transition itself. Turning finally from electronic conduction to ionic conduction, we study hydrogen transport and optical properties in BaCeO3. We establish a new understanding of electron localization in this material and explain the results of luminescence experiments. In SrCeO3, cation vacancies are shown to be an important source of proton traps which impede diffusion, and known benefits of doping are explained as resulting from a suppression of these vacancies. In each material, advances in fundamental understanding guide experiment and advance applications. Electronic structure ; Dopant ; Condensed matter physics ; Ionic bonding ; Density functional theory ; Semiconductor ; Mott insulator ; Doping ; Materials science ; Engineering physics ; Chemistry ; Physics ; Computational chemistry ; Quantum mechanics ; Ion Electronic and Structural Properties of Oxides ; Advanced Condensed Matter Physics ; Physics of Superconductivity and Magnetism
Authors: Anish Rao | Govind Sasi Kumar | Soumendu Roy | T. R. Ajesh | Gayathri Devatha | Pramod P. Pillai
Source: ChemRxiv (preprint, 2018-10-15)
Field: Chemistry — Electrochemistry

Emergence of Selectivity in Inherently Nonselective Gold Nanoparticles Through Preferential Breaking of Interparticle Interactions We demonstrate a fundamentally unique identification strategy to impart selectivity to a traditionally and inherently nonselective carboxylate-functionalized gold-nanoparticles ([-] AuNPs), without the aid of any analyte specific ligands. The common practice is to use the ability of divalent ions to trigger the aggregation process in a kinetically trapped dispersed solution of [-] AuNPs. Aggregation of NPs being a thermodynamically favourable process will result in a uniform and nonselective turn-off response from most of the strongly binding divalent ions. Our approach is to use the abilities of various divalent ions to break a thermodynamically stable inter-nanoparticle precipitates containing [+] and [-] AuNPs (nanoionic precipitates), as the means of identification. Importantly both [+] and [-] AuNPs, independently, were ‘blind’ in terms of selectivity towards divalent ions. Remarkably, a hybrid-system composed of such nonselective nanoparticles was able to discriminate between the hard-to-distinguish pair of Pb2+ and Cd2+ ions. The rationale is that only the strongest of strongly binding ions will be able to break the interactions between the NP precipitates (thermodynamically stable state) and re-disperse them back in solution (kinetically trapped state). This is in stark contrast with the conventional idea of forming an interaction between NPs and divalent ions, with the help of analyte-specific ligands. Divalent ; Selectivity ; Chemistry ; Colloidal gold ; Nanoparticle ; Ion ; Analyte ; Combinatorial chemistry ; Nanotechnology ; Inorganic chemistry ; Chemical physics ; Catalysis ; Materials science ; Physical chemistry ; Organic chemistry Electrochemical Analysis and Applications ; Gold and Silver Nanoparticles Synthesis and Applications ; Nanocluster Synthesis and Applications
Authors: B. Raftaritangabi
Source: Data Archiving and Networked Services (DANS) (article, 2018-01-01)
Field: Materials Science — Surfaces, Coatings and Films

Drift-Diffusion-Reaction Model for Time-Domain Analysis of Charging Phenomena in Electron-Beam Irradiated Insulators Electron microscopes take advantage of a beam of electrons to illuminate a&lt;br/&gt;specimen and extract the needed information from the interaction of particles&lt;br/&gt;with matter in order to produce a high resolution image. The main research&lt;br/&gt;question of the present study arose from the fact that this resolution is degraded&lt;br/&gt;when a given specimen contains insulating materials. In the electron&lt;br/&gt;microscopy of insulators the effect behind the degradation of an image resolution&lt;br/&gt;is known as the charging effect. The charging effect needs to be studied&lt;br/&gt;and understood, in particular, since biological specimens are either insulators&lt;br/&gt;or contain insulating parts. Electron microscope ; Electron ; Cathode ray ; Resolution (logic) ; Electron beam processing ; Irradiation ; Diffusion ; Materials science ; Image resolution ; Beam (structure) ; Optics ; Degradation (telecommunications) ; Chemical physics ; Nanotechnology ; Chemistry ; Physics ; Computer science ; Electronic engineering ; Nuclear physics ; Engineering ; Artificial intelligence Electron and X-Ray Spectroscopy Techniques ; Advancements in Photolithography Techniques ; Hydrogen embrittlement and corrosion behaviors in metals
Authors: Aparna Nambiar
Source: OpenCommons - UConn (University of Connecticut) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Development of Tools for a 3D Reconstructed Intracortical Volume Around Microelectrode Arrays Extensive research using penetrating electrodes implanted in the central and peripheral nervous systems has been performed for many decades with significant advances made in recent years. While these penetrating devices provide proximity to individual neurons in-vivo and perform effectively for several months, they are prone to failure over a year and longer. 2D Histology studies using serial tissue sections have been extremely insightful over the years in identifying and quantifying most of these factors such as astrocytic scar formation, microgliosis, and neuronal death, around the implant sites. However, there are significant limitations of 2D histological studies in providing a holistic picture of the problems occurring at the electrode-tissue interface. In this study, we present 3D reconstruction of serial sections to overcome the limitations of 2D histological analysis. We used a cohort of software: XuvStitchTM (XuvTools), AutoAlignerTM (Bitplane AG), and ImarisTM (Bitplane AG), and coupled these with MATLAB (The MathWorks, Inc.) programming to correct warping effects and misalignment issues. Once the 3D image volume is reconstructed, we were able to use features of ImarisTM to quantify neuronal densities and astrocytic scar tissue densities around the electrode tips of a hybrid microelectrode array. This study also demonstrated advantages of quantifying around different types of microelectrodes of a hybrid array in the same intracortical space eliminating confounding factors such as varying implantation sites, lengths of study, different animals, so on and so forth. Thereby, the performance of the microelectrodes can be attributed solely to device material properties and device fabrication process. Volume (thermodynamics) ; Microelectrode ; Computer science ; Chemistry ; Physics ; Electrode Anodic Oxide Films and Nanostructures
Authors: Christopher David-James Aretz
Source: Digital Commons - DU (University of Denver) (article, 2018-01-01)
Field: Chemistry — Inorganic Chemistry

Selective Carbon-Carbon Bond Formation Promoted by Divalent Samarium Reagents Three efficient methods for synthesis of five membered carbocycles, a highly understudied product motif in samarium(II) chemistry, were explored and optimized. These methods utilized simple starting materials to generate linear substrates with functional groups that are reactive towards samarium(II) iodide. The three methods explored were the Reformatsky-aldol, Reformatsky-alkylation, and pinacol cyclizations. The critical discovery for efficient formation of the Reformatsky-aldol and pinacol carbocycles products was the use of lithium bromide. This addition of lithium bromide facilitates easy in situ formation of samarium(II) bromide. The Reformatsky-alkylation cyclization was a newly realized reaction employing samarium enolates. Two of the three methods, the Reformatsky-aldol and pinacol, generated carbocycles with multiple functional groups attached. These reactions were able to proceed with exceptional diastereoselectivity. In addition to the new methods for five membered, a lead results towards asymmetric samarium (II) Reformatsky-aldol cyclization was explored. This provided the product with modest enantiomeric excess. The mechanism of the alkylation reaction was studied with the use of spin trapped products and electron paramagnetic resonance spectroscopy (EPR). By analyzing the spectra of the resulting spin trapped products the initial site of reduction being the carbon-bromine bond was supported. This was supported by simulated spectra of the spin trapped experiments and by performing the spin trapping experiments on an alpha-deuterated substrate. This substrate was synthesized by performing a hydrogen-deuterium exchange experiment. Another divalent samarium reagent, allylsamarium bromide, was studied in reactions with isatin and isatin derivatives. The samarium reagent has both nucleophilic and reductive properties. Substituted isatins were able to be allylated at the three-position forming 3-allyl oxindoles. In addition, two isatin derivatives, oxindole and isatoic anhydrides, were reacted with allylsamarium bromide. The reaction of substituted oxindoles yielded allylated indoles and indolines. Whereas, the reaction of substituted isatoic anhydrides yielded the double allylated and ring opened product. All of these compounds provided privileged scaffolds and/or compounds bearing multiple functional groups. Samarium ; Divalent ; Chemistry ; Reagent ; Carbon fibers ; Bond ; Inorganic chemistry ; Organic chemistry ; Business ; Materials science Asymmetric Hydrogenation and Catalysis ; Organometallic Complex Synthesis and Catalysis ; Synthetic Organic Chemistry Methods
Authors: Zhen Xing
Source: W&M Publish (College of William & Mary) (article, 2018-01-01)
Field: Materials Science — Electronic, Optical and Magnetic Materials

Charge Dynamics In The Metallic And Superconducting States Of The Electron-Doped 122-Type Iron Arsenides Understanding charge dynamics and the origin of superconductivity in iron-based materials is one of the most important topics in condensed matter physics. Among different structures of iron-based materials, 122-type iron arsenides are of considerable interest due to their diverse phase diagrams, relatively high superconducting transition temperatures, and the availability of high quality single crystals. In this dissertation, we study temperature and frequency dependence of charge dynamics of the electron-doped 122-type iron arsenides in the metallic and superconducting states using broadband infrared spectroscopy at cryogenic temperatures. We have investigated the charge dynamics and the nature of many-body interactions in metallic La- and Pr- doped CaFe2As2. From the infrared part of the optical conductivity, we discover that the scattering rate of mobile carriers above 200 K exhibits saturation at the Mott-Ioffe-Regel limit of metallic transport. However, the dc resistivity continues to increase with temperature above 200 K due to the loss of Drude spectral weight. The loss of Drude spectral weight with increasing temperature is seen in a wide temperature range in the uncollapsed tetragonal phase, and this spectral weight is recovered at energy scales about one order of magnitude larger than the Fermi energy scale in these semimetals. The phenomena noted above have been observed previously in other correlated metals in which the dominant interactions are electronic in origin. Further evidence of significant electron-electron interactions is obtained from the presence of quadratic temperature and frequency-dependence scattering rate at low temperatures and frequencies in the uncollapsed tetragonal structures of La- and Pr-doped CaFe2As2. We also observe weakening of electronic correlations and a decrease of Drude spectral weight upon the transition to the collapsed tetragonal phase in Pr-doped CaFe2As2. We have measured infrared reflectance spectra of BaFe1.9Pt0.1As2 in the normal and superconducting states. We find that this superconductor has fully gapped Fermi surfaces. Importantly, we observe strong-coupling electron-boson interaction features in the infrared absorption spectra. By using two modeling methods which include strong-coupling effects via the Eliashberg function, we obtain a good quantitative description of the energy gaps and the temperature dependent strong-coupling features. Our experimental data and analysis provide compelling evidence that superconductivity in BaFe1.9Pt0.1As2 is induced by the coupling of electrons to a low energy bosonic mode. Condensed matter physics ; Superconductivity ; Doping ; Charge (physics) ; Electron ; Metal ; Materials science ; Physics ; Quantum mechanics ; Metallurgy Iron-based superconductors research ; Surface and Thin Film Phenomena ; Rare-earth and actinide compounds
Authors: Anne Asiko Okanga | John Okoth Ogur | Victor Dinda
Source: Zenodo (CERN European Organization for Nuclear Research) (article, 2018-07-13)
Field: Materials Science — Polymers and Plastics

Regulatory Body Characteristics Influencing Performance In The Nck Examinations. Quality education is crucial to the development of any profession. The need to produce nurses capable of functioning as safe practitioners in the health care is key. This has been necessitated by the increasing cost of health care. It therefore demands that nurses should possess recognized qualification before they can be registered and practice legally in any country. This study examined regulatory body characteristics that influence performance in the Nursing Council of Kenya examinations. The poor performance reported in the recent past years has warranted the need to conduct an investigation to unravel the possible factors with the regulatory body that could be associated with poor performance. The study may be used by NCK to address gaps identified in examination process to enhance validity in the NCK examinations. The study design was qualitative study. Data was collected retrospectively for a period of three years. Study site was the NCK and schools of nursing country wide. Study population comprised the heads of schools of nursing and the head of department concerned with examination at the NCK. Cluster and purposive sampling were done for key informants interviewed from nursing schools. Qualitative data was recorded and transcribed for content analysis. The study found the NCK examination to be susceptible toreduced validity resulting from format of examination, invigilation, marking and moderation procedures used and examination malpractices likely to occur. In conclusion the study reported reduced validity of the NCK examinations. The study recommended the NCK to consider revising format of examination in order to increase examination validity and to benchmark with other examinations such as N-CLEX and adopt other means of processing the examination. Business Textile materials and evaluations