scholarly journals Structural Evolution of Burmese Amber during Petrifaction Based on a Comparison of the Spectral Characteristics of Amber, Copal, and Rosin

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Feng Bai ◽  
Huifang Liang ◽  
Hongting Qu
Keyword(s):  
Structural Changes ◽  
Spectral Characteristics ◽  
Structural Evolution ◽  
Degree Of Polymerization ◽  
Organic Polymer ◽  
Polymer Mixture ◽  
Burmese Amber ◽  
Solubility Study ◽  
Visible Spectra ◽  
Peak Areas

This paper presents a spectroscopic analysis and solubility study of rosin, copal, and Burmese amber samples to reveal the structural changes that occur during amber formation. The infrared spectra indicate that during the long geological process of amber formation, small resin molecules first crosslinked and slowly oxidized, eventually forming a stable organic polymer mixture. An analysis of Raman peak areas demonstrated that among the tested samples, the degree of polymerization is highest in Burmese amber and lowest in rosin. Ultraviolet-visible spectra indicate the presence of unsaturated bonds (e.g., carbonyl groups) or conjugated systems in Burmese amber, copal, and rosin. The evaluation of amber, rosin, and copal solubility in six solvents (ethanol, acetone, 1,4-dioxane, ethylacetate, N,N-dimethylamide, and dichloromethane) demonstrated that solubility decreases in the following order: rosin > copal > Burmese amber. Together, the results suggest that the structure of Burmese amber includes large organic molecules containing six-membered rings along with CH2, CH3, C=O, C=C, C–O, and C–C groups.

Effects of Metal Stress on Visible/Near-Infrared Reflectance Spectra of Vegetation

2011 ◽  
Vol 347-353 ◽  
pp. 2735-2738 ◽  
Author(s):  
Guang Yu Chi ◽  
Yi Shi ◽  
Xin Chen ◽  
Jian Ma ◽  
Tai Hui Zheng
Keyword(s):  
Heavy Metal ◽  
Structural Changes ◽  
Near Infrared ◽  
Leaf Surface ◽  
Spectral Response ◽  
Spectral Characteristics ◽  
Surface Characteristics ◽  
Heavy Metal Stress ◽  
Metal Stress ◽  
Near Infrared Reflectance

Vegetation which suffers from heavy metal stresses can cause changes of leaf color, shape and structural changes. The spectral characteristics of vegetation leaves is related to leaf thickness, leaf surface characteristics, the content of water, chlorophyll and other pigments. So the eco-physiology changes of plants can be reflected by spectral reflectance. Studies on the spectral response of vegetation to heavy metal stress can provide a theoretical basis for remote sensing monitoring of metal pollution in soils. In recent decades, there are substantial amounts of literature exploring the effects of heavy metals on vegetation spectra.

scholarly journals Structural Evolution in Wet Mechanically Alloyed Co-Fe-(Ta,W)-B Alloys

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 800
Author(s):  
Vladimír Girman ◽  
Maksym Lisnichuk ◽  
Daria Yudina ◽  
Miloš Matvija ◽  
Pavol Sovák ◽  
...  
Keyword(s):  
Structural Changes ◽  
Magnetic Measurements ◽  
Structural Evolution ◽  
High Energy ◽  
Control Agent ◽  
X Ray Diffraction ◽  
Mechanically Alloyed ◽  
X Ray ◽  
Transmission Electron ◽  
X Ray Absorption

In the present study, the effect of wet mechanical alloying (MA) on the glass-forming ability (GFA) of Co43Fe20X5.5B31.5 (X = Ta, W) alloys was studied. The structural evolution during MA was investigated using high-energy X-ray diffraction, X-ray absorption spectroscopy, high-resolution transmission electron microscopy and magnetic measurements. Pair distribution function and extended X-ray absorption fine structure spectroscopy were used to characterize local atomic structure at various stages of MA. Besides structural changes, the magnetic properties of both compositions were investigated employing a vibrating sample magnetometer and thermomagnetic measurements. It was shown that using hexane as a process control agent during wet MA resulted in the formation of fully amorphous Co-Fe-Ta-B powder material at a shorter milling time (100 h) as compared to dry MA. It has also been shown that substituting Ta with W effectively suppresses GFA. After 100 h of MA of Co-Fe-W-B mixture, a nanocomposite material consisting of amorphous and nanocrystalline bcc-W phase was synthesized.

Applicability of Exposure Reciprocity Law for Fast Polymerization of Restorative Composites Containing Various Photoinitiating Systems

2021 ◽  
Author(s):  
A Tichy ◽  
P Bradna
Keyword(s):  
High Power ◽  
Irradiation Time ◽  
Spectral Characteristics ◽  
Degree Of Polymerization ◽  
High Irradiance ◽  
Bottom Surface ◽  
Surface Microhardness ◽  
Radiant Exposure ◽  
Reciprocity Law ◽  
Restorative Composites

SUMMARY Objectives: The exposure reciprocity law (ERL) has been used to calculate the optimal irradiation time of dental composites. This study examined the applicability of ERL for fast polymerization of restorative composites containing various photoinitiating systems using a high-power multi-peak light-emitting diode (LED) lamp. Methods: Three commercial composites differing in photoinitiating systems were tested: Filtek Ultimate Universal Restorative (FU) with a camphorquinone-amine (CQ-A) photoinitiating system, Tetric EvoCeram (TEC) with CQ-A and (2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and Estelite Σ Quick (ESQ) with CQ and a radical amplified photopolymerization (RAP) initiator. Specimens 2-mm thick were polymerized using a high-power multipeak LED lamp (Valo) at 3 pairs of radiant exposures (referred to as low, moderate, and high) ranging from 15.8–26.7 J/cm2. They were achieved by different combinations of irradiation time (5–20 seconds) and irradiance (1300–2980 mW/cm2) as determined with a calibrated spectrometer. Knoop microhardness was measured 1, 24, and 168 hours after polymerization on specimen top (irradiated) and bottom surfaces to characterize the degree of polymerization. The results were statistically analyzed using a three-way analysis of variance and Tukey’s post hoc tests, α = 0.05. Results: Microhardness increased with radiant exposure and except for ESQ, top-surface microhardness was significantly higher than that on bottom surfaces. Combinations of high irradiance and short irradiation time significantly increased the top-surface microhardness of TEC at low and moderate radiant exposures, and the bottom-surface microhardness of FU at a low radiant exposure. In contrast, the microhardness of ESQ on both surfaces at high radiant exposure increased significantly when low irradiance and long irradiation time were used. With all tested composites, bottom-surface microhardness obtained at low radiant exposure was below 80% of the maximum top-surface microhardness, indicating insufficient polymerization. Conclusion: Combinations of irradiance and irradiation time had a significant effect on microhardness, which was affected by photoinitiators and the optical properties of composites as well as spectral characteristics of the polymerization lamp. Therefore, ERL cannot be universally applied for the calculation of optimal composite irradiation time. Despite high irradiance, fast polymerization led to insufficient bottom-surface microhardness, suggesting the necessity to also characterize the degree of polymerization on the bottom surfaces of composite increments when assessing the validity of ERL.

scholarly journals Studying the structural and electronic effects of substituted (Bi0.5Na0.5)TiO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C1522-C1522
Author(s):  
Peter Blanchard ◽  
Brendan Kennedy ◽  
Chris Ling
Keyword(s):  
Solid Solutions ◽  
Structural Changes ◽  
Structural Evolution ◽  
Rhombohedral Phase ◽  
Rhombohedral Structure ◽  
Electronic Effects ◽  
Spectra Analysis ◽  
Space Group ◽  
Industry Standard ◽  
Made In

Significant efforts have been made in the development of (Bi0.5Na0.5)TiO3 ferroelectrics as an alternative to the lead-based industry standard PbTi1-xZrxO3.[1] It has also been shown that doping the A- and B-site of (Bi0.5Na0.5)TiO3 can greatly improve the ferroelectric behavior of these materials,[2] possibly due to the formation of two or more ferroelectric phases at a morphotropic phase boundary (MPB). As such, there is a significant interest in understanding the structural changes in (Bi0.5Na0.5)TiO3-based solid solutions. (Bi0.5Na0.5)TiO3 was originally described as adopting a rhombohedral structure in space group R3c, However, the accuracy of this description has been greatly debated. It was recently suggested that (Bi0.5Na0.5)TiO3 actually adopts a monoclinic structure in space group Cc.[3] Given this recent controversy, we investigated the structural evolution of (Bi0.5Na0.5)TiO3-based solid solutions, particularly the (Bi0.5Na0.5)Ti1-xZrxO3 and (1-x)(Bi0.5Na0.5)TiO3–xBiFeO3 solid solutions., using both diffraction and spectroscopy techniques. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Diffraction analysis showed that doping (Bi0.5Na0.5)TiO3 with a small amount of (Bi0.5Na0.5)ZrO3 and BiFeO3 can stabilizes the rhombohedral phase. The Ti/Fe K-edge and Zr L3-edge XANES spectra analysis was performed to determine the effects doping has on the local displacement of the B-site cations.

Ab initio calculations of scytonemin derivatives of relevance to extremophile characterization by Raman spectroscopy

2010 ◽  
Vol 368 (1922) ◽  
pp. 3193-3203 ◽  
Author(s):  
Tereza Varnali ◽  
Howell G. M. Edwards
Keyword(s):  
Ab Initio ◽  
Structural Changes ◽  
Spectral Characteristics ◽  
Special Role ◽  
Absorption Bands ◽  
Parent Molecule ◽  
Detailed Structural Analysis ◽  
Protective Strategy ◽  
Terrestrial Environments ◽  
Martian Regolith

The recognition that scytonemin, the radiation protectant pigment produced by extremophilic cyanobacterial colonies in stressed terrestrial environments, is a key biomarker for extinct or extant life preserved in geological scenarios is critically important for the detection of life signatures by remote analytical instrumentation on planetary surfaces and subsurfaces. The ExoMars mission to seek life signatures on Mars is just one experiment that will rely upon the detection of molecules such as scytonemin in the Martian regolith. Following a detailed structural analysis of the parent scytonemin, we report here for the first time a similar analysis of several of its methoxy derivatives that have recently been extracted from stressed cyanobacteria. Ab initio calculations have been carried out to determine the most stable molecular configurations, and the implications of the structural changes imposed by the methoxy group additions on the spectral characteristics of the parent molecule are discussed. The calculated electronic absorption bands of the derivative molecules reveal that their capability of removing UVA wavelengths is removed while preserving the ability to absorb the shorter wavelength UVB and UVC radiation, in contrast to scytonemin itself. This is indicative of a special role for these molecules in the protective strategy of the cyanobacterial extremophiles.

scholarly journals Mapping the evolution of the central government apparatus in China

2018 ◽  
Vol 86 (1) ◽  
pp. 80-97 ◽  
Author(s):  
Liang Ma ◽  
Tom Christensen
Keyword(s):  
Organization Theory ◽  
Structural Changes ◽  
Central Government ◽  
Structural Evolution ◽  
Structural Reforms ◽  
Multiple Perspectives ◽  
Institutional Reforms ◽  
Cultural Elements ◽  
Interagency Coordination ◽  
Political Cycles

The structure of political and administrative institutions is important for achieving public goals. It is not fixed, however, but may change as a result of environmental and cultural processes or because of changes in leadership. Structural changes in the central government apparatus feature prominently in the recent strand of reform and change literature, but we know little about structural changes in contexts other than Western democracies. In this article, we analyze the main types of and possible reasons for structural changes in the central government apparatus in China over the past 70 years. We find interesting patterns of structural change in line with administrative developments. Using the multiple perspectives of organization theory, these can be primarily explained by political cycles or action taken by the central leadership, but they have also been influenced by cultural elements, economic growth, and societal transformation. Points for practitioners We document the key patterns of organizational restructuring in China’s central government from 1949 to 2016. Political cycles and economic reform and development are found to be the key drivers of structural evolution. The results show that the political will of top leaders plays a crucial role in navigating structural reforms, yet institutional reforms are still largely confined to rhetoric and symbolism without substantively transforming the landscape of government architecture. Sustained structural reforms are difficult to achieve successfully, which suggests that alternative avenues may be required to streamline administrative processes and improve interagency coordination.

scholarly journals Extensive sequence and structural evolution of Arginase 2 inhibitory antibodies enabled by an unbiased approach to affinity maturation

2020 ◽  
Vol 117 (29) ◽  
pp. 16949-16960 ◽  
Author(s):  
Denice T. Y. Chan ◽  
Lesley Jenkinson ◽  
Stuart W. Haynes ◽  
Mark Austin ◽  
Agata Diamandakis ◽  
...  
Keyword(s):  
Structural Changes ◽  
Structural Evolution ◽  
Affinity Maturation ◽  
Antibody Engineering ◽  
Inhibitory Antibody ◽  
Extensive Sequence ◽  
Shape Complementarity ◽  
Complementarity Determining Regions ◽  
Inhibition Potency

Affinity maturation is a powerful technique in antibody engineering for the in vitro evolution of antigen binding interactions. Key to the success of this process is the expansion of sequence and combinatorial diversity to increase the structural repertoire from which superior binding variants may be selected. However, conventional strategies are often restrictive and only focus on small regions of the antibody at a time. In this study, we used a method that combined antibody chain shuffling and a staggered-extension process to produce unbiased libraries, which recombined beneficial mutations from all six complementarity-determining regions (CDRs) in the affinity maturation of an inhibitory antibody to Arginase 2 (ARG2). We made use of the vast display capacity of ribosome display to accommodate the sequence space required for the diverse library builds. Further diversity was introduced through pool maturation to optimize seven leads of interest simultaneously. This resulted in antibodies with substantial improvements in binding properties and inhibition potency. The extensive sequence changes resulting from this approach were translated into striking structural changes for parent and affinity-matured antibodies bound to ARG2, with a large reorientation of the binding paratope facilitating increases in contact surface and shape complementarity to the antigen. The considerable gains in therapeutic properties seen from extensive sequence and structural evolution of the parent ARG2 inhibitory antibody clearly illustrate the advantages of the unbiased approach developed, which was key to the identification of high-affinity antibodies with the desired inhibitory potency and specificity.

scholarly journals Direct observation of oxygen-vacancy formation and structural changes in Bi2WO6 nanoflakes induced by electron irradiation

2019 ◽  
Vol 10 ◽  
pp. 1434-1442 ◽  
Author(s):  
Hong-long Shi ◽  
Bin Zou ◽  
Zi-an Li ◽  
Min-ting Luo ◽  
Wen-zhong Wang
Keyword(s):  
Electron Irradiation ◽  
Oxygen Vacancies ◽  
Structural Changes ◽  
Cluster Formation ◽  
Energetic Electron ◽  
Structural Evolution ◽  
Formation Mechanisms ◽  
Tungsten Oxides ◽  
Transmission Electron ◽  
Oxygen Vacancy Formation

The prominent role of oxygen vacancies in the photocatalytic performance of bismuth tungsten oxides is well recognized, while the underlying formation mechanisms remain poorly understood. Here, we use the transmission electron microscopy to investigate the formation of oxygen vacancies and the structural evolution of Bi2WO6 under in situ electron irradiation. Our experimental results reveal that under 200 keV electron irradiation, the breaking of relatively weak Bi–O bonds leads to the formation of oxygen vacancies in Bi2WO6. With prolonged electron irradiation, the reduced Bi cations tend to form Bi clusters on the nanoflake surfaces, and the oxygen atoms are released from the nanoflakes, while the W–O networks reconstruct to form WO3. A possible mechanism that accounts for the observed processes of Bi cluster formation and oxygen release under energetic electron irradiation is also discussed.

DEVELOPMENT OF A METHOD FOR SYNTHESIZING AN APERTURE DIAPHRAGM IN HYPERSPECTRAL REMOTE SENSING SYSTEMS FOR EARTH

2020 ◽  
pp. 23-30
Author(s):  
A. Yu. Kuznecov ◽  
A. A. Sadikova ◽  
V. I. Gornyj ◽  
I. Sh. Latypov
Keyword(s):  
Remote Sensing ◽  
Neural Networks ◽  
Structural Changes ◽  
Spectral Characteristics ◽  
Optical Systems ◽  
Radiometric Calibration ◽  
Radial Basis Network ◽  
Sensing Systems ◽  
The Earth ◽  
Remote Sensing Systems

The aim of the work is to research and develop methods for synthesizing aperture in hyperspectral systems for remote sensing of the Earth to reduce weight and size characteristics by applying methods of program-algorithmic processing of the input signal and implementing the synthesized aperture. A method of neural networks for deconvolution on the construction of a radial basis network is developed. A method has been developed to increase the synthesis of apertures in hyperspectral systems for remote sensing of the Earth. A method for increasing the spatial resolution of images obtained by optical systems for remote sensing of the Earth is described. A method for radiometric calibration of output data has been developed, which allows universalizing the analysis of spectral characteristics. In the process, to achieve the goals were used: methods of spectral optics, mathematical analysis and statistics, methods of processing images and signals. The project results contribute to the reduction of overall weight and cost characteristics and the possibility of synthesizing the aperture at the exit of the polychromator, which will avoid the use of expensive camera lenses in hyperspectral systems of remote sensing of the Earth. The developed methods for synthesizing aperture in hyperspectral systems of remote sensing of the Earth differ from the existing ones in that the receiving device for the video signal does not contain structural changes, and they contain the function of the algorithmic apparatus, which includes the analysis of the functions of the scattering point, the deconvolution of the recorded signal is performed by the method of neural networks after the stage learning.

A determination of structural evolution during the processing of glycol-based, sol-gel derived ceramics through the study of ferrimagnetic interactions

2007 ◽  
Vol 22 (11) ◽  
pp. 3152-3157 ◽  
Author(s):  
Edward J. Donahue ◽  
Michael Ng ◽  
Patrick Li
Keyword(s):  
Thermogravimetric Analysis ◽  
Structural Changes ◽  
Sol Gel ◽  
Structural Evolution ◽  
X Ray Diffraction ◽  
Straight Chain ◽  
X Ray ◽  
Decomposition Pathway ◽  
Ferrimagnetic Ordering

This work studies the chemical and structural changes that occur in sols upon heating to form ceramics. Ferrimagnetic Y3Fe5O12 (YIG) was chosen because the geometric and structural constraint of ferrimagnetic interactions allow for a direct measurement of the degree of well-defined structure present within the sol at various stages of development. Glycolate sols of 8% mol total metal were prepared using Y(NO3)3 and Fe(NO3)3 hydrates in stoichiometric ratios. Terminal straight-chain diols were used, ranging from 1,2-ethanediol to 1,6-hexanediol. The temperatures at which mass change occurred during heating were determined by thermogravimetric analysis. Samples were heated to these temperatures and examined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction, and magnetometry to determine chemical, structural, and magnetic changes. Ferrimagnetic ordering was present after the first heating step. Defined structure, determined by x-ray, occurred in the penultimate step. Analysis of FTIR spectra, in conjunction with the results of thermogravimetric analysis, revealed a predictable decomposition pathway.

Sign in / Sign up

Export Citation Format

Share Document