D -region electron distributions in middle latitudes deduced from the reflexion of long radio waves

1966 ◽  
Vol 291 (1426) ◽  
pp. 413-437 ◽  
Keyword(s):  
Electron Concentration ◽  
Electron Distribution ◽  
Collision Frequency ◽  
Structural Features ◽  
Height Distribution ◽  
Radio Waves ◽  
Height Range ◽  
Small Peak ◽  
Wide Range ◽  
Full Wave Analysis

A method of full-wave analysis is used to compute the theoretical values of reflexion and conversion coefficients of long and very long radio waves incident on a horizontally stratified ionosphere having a postulated height distribution of electron concentration and collision frequency. With reasonable values of collision frequency (§4 and figure 1), the electron distribution is then progressively changed until the computed values of the reflexion parameters agree with experimental measurements over a range of frequencies from 16 to 100 kc/s at both steep and oblique incidence. Height distributions of electrons which would explain the results of experiments made at different times of the day, the year, the solar cycle, and during an eclipse, are presented in figures 2 to 7. It is shown that these distributions are consistent with a wide range of experimental results on other frequencies. Important structural features in the electron distribution are noticed: by day (figure 2) there is a small peak of electron concentration near 64 km, a sharp gradient near 74 km, and a shallow gradient in the height range 75 to 88 km which joins the bottomside of the E -layer; at night (figure 7) electron concentrations below 80 km are very small, and there is a sharp gradient near 90 km. The electron concentrations above and below 70 km depend in different ways on the intensity of solar radiation.

Studies on the ionization produced by metallic salts in flames. IV. The stability of gaseous alkali hydroxides in flames

1952 ◽  
Vol 211 (1104) ◽  
pp. 58-74 ◽  
Keyword(s):  
Electron Concentration ◽  
Direct Method ◽  
Stoichiometric Composition ◽  
Heat Of Formation ◽  
Ion Concentration ◽  
Radio Waves ◽  
Kcal Mole ◽  
Hydroxyl Ion ◽  
Wide Range ◽  
Alkali Hydroxides

The electron concentration produced by the addition of alkali metal salts to a wide range of hydrogen/air flames extending to the air-rich side of stoichiometric composition has been measured by the method of attenuation of centimetric radio waves. Considerable deviations from the predicted behaviour on the basis of the known ionization potentials of the metals and the measured temperatures have been observed. The main effect noted is that for two flames of the same temperature, but on opposite sides of stoichiometric composition, the air-rich one always shows a markedly lower attenuation, an effect which is by far the most pronounced in the case of caesium. The electron concentration throughout is considerably below the predicted level. Simple statistical calculations have shown that the formation of gaseous ion pair molecules of the alkali hydroxides by combination with the hydroxyl radicals in the flame is plausible, and an analysis of the electron concentrations on this basis has shown that the results are compatible with removal of a large amount of caesium as hydroxide, but not of potassium and sodium. This agrees with the expected difference in energy of formation of caesium and potassium hydroxides, from the gaseous metal and hydroxyl, of about 5 kcal/mole. It has not proved possible to explain the whole of the deviations of the electron concentration in this way, but by incorporation of a further effect, of production of hydroxyl ions, which is independent of the metal added, a complete resolution may be obtained. The concentrations of hydroxyl ion predicted by the analysis show agreement both with the observed discrepancy with the theoretical electron concentration, and with the order of magnitude of hydroxyl ion concentration obtained earlier by an independent and more direct method (Smith & Sugden 1952). The hydroxyl radical concentrations implied by this analysis show excellent agreement with those obtained from thermodynamic calculation of the burned gas composition at equilibrium. Values for the heat of formation of gaseous potassium hydroxide and gaseous caesium hydroxide, from the gaseous metal and hydroxyl, which the data require are 87.5 ± 3 and 92.5 ± 3 kcal/mole respectively. The analysis of the results further implies an electron affinity for gaseous OH of 69 ± 5 kcal/mole, which agrees reasonably with the value obtained previously from flame measurements of 62 ± 6 kcal/mole.

Collision frequency of electrons in the F region

1970 ◽  
Vol 48 (6) ◽  
pp. 653-658 ◽  
Author(s):  
C. S. G. K. Setty ◽  
A. R. Jain ◽  
M. K. Vyawahare
Keyword(s):  
Collision Frequency ◽  
Extraordinary Wave ◽  
Early Morning ◽  
Radio Waves ◽  
Height Range ◽  
F Region ◽  
Geographical Latitude ◽  
Late Evening ◽  
Wave Modes

The collision frequency of electrons in the F region of the ionosphere has been measured at Delhi (geographical latitude 28°38′ N, geographical longitude 77°13′ E) using a method similar to that suggested by Appleton. The amplitude and group path of short radio waves vertically incident on the F region of the ionosphere have been measured simultaneously at a suitable frequency (for both the ordinary and extraordinary wave modes) in early morning and late evening hours, corresponding to times of appearance and disappearance of the echo, respectively. Simultaneous changes in amplitude and group path are related to deduce the collision frequency. Some selected records taken near the time of sunrise have been analyzed and the values of collision frequency are found to be (4.2 ± 0.5) × 103 and (3.5 ± 0.5) × 103 s−1 for the ordinary and extraordinary waves, respectively, in the true-height range of 270–310 km.

Über ein Verfahren zur gleichzeitigen Bestimmung von Elektronenkonzentration und Elektronenstoßzahl in einem homogenen isotropen oder in einem langsam veränderlichen Plasma

1970 ◽  
Vol 25 (1) ◽  
pp. 106-114
Author(s):  
W. Muschler
Keyword(s):  
Refractive Index ◽  
Electron Concentration ◽  
Collision Frequency ◽  
Complex Refractive Index ◽  
Electron Collision ◽  
Height Range ◽  
Reflected Waves ◽  
Electron Collision Frequency ◽  
D Region

Abstract A method is described, which allows determination of the complex refractive index of a plasma by separate measurement of the E-and H-component of an electromagnetic wave. By means of the complex refractive index simultaneously electron concentration and electron collision frequency of the medium can be stated.The measuring frequency depends upon absorption, precision requirements, and - for a locally varying medium - upon the availability range of theory used.General considerations are applied to a plasma model (terrestrial ionosphere without magnetic field): Simultaneous measurement of electron concentration and electron collision frequency should be well possible within a height range corresponding to the terrestrial D-region. In higher regions determination of the (decreasing) electron collision frequency becomes more and more difficult, whereas possibilities for determination of the (increasing) electron concentration seem to improve.The influence of reflected waves is considered in a following paper 4.

pH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase

2019 ◽  
Vol 26 (10) ◽  
pp. 743-750 ◽  
Author(s):  
Remya Radha ◽  
Sathyanarayana N. Gummadi
Keyword(s):  
Vibrio Cholerae ◽  
Conformational Changes ◽  
Kinetic Studies ◽  
Structural Features ◽  
Structure Stability ◽  
Kcal Mole ◽  
Scanning Calorimetry ◽  
Wide Range ◽  
Ph Dependent ◽  
Ph Range

Background:pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry.Objective:The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase.Methods:Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase.Results:The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1.Conclusion:The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0–7.0.

Application of Nitrogen Heterocyclic Carbenes in Organocatalysis

2020 ◽  
Vol 09 ◽  
Author(s):  
Minita Ojha ◽  
R. K. Bansal
Keyword(s):  
Asymmetric Catalysis ◽  
Building Blocks ◽  
Structural Features ◽  
Heterocyclic Carbenes ◽  
Stetter Reaction ◽  
Metal Pollutants ◽  
Synthetic Strategy ◽  
Wide Range ◽  
Benzoin Condensation ◽  
Nitrogen Heterocyclic

Background: During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes (NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods: By manipulating structural features and selecting appropriate substituent groups, it has been possible to control the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of Nalkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction. Results: The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions, isomerization, etc. The present review includes all these examples published during the last 10 years, i.e. from 2010 till date. Conclusion: The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They provide the synthetic strategy which does not burden the environment with metal pollutants and thus fit in the Green Chemistry.

scholarly journals Ring-Forming Polymerization toward Perfluorocyclobutyl and Ortho-Diynylarene-Derived Materials: From Synthesis to Practical Applications

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1486
Author(s):  
Eugene B. Caldona ◽  
Ernesto I. Borrego ◽  
Ketki E. Shelar ◽  
Karl M. Mukeba ◽  
Dennis W. Smith
Keyword(s):  
Chemical Resistance ◽  
Structural Features ◽  
Review Article ◽  
Aryl Ether ◽  
Aromatic Rings ◽  
Practical Applications ◽  
Repeat Units ◽  
Wide Range ◽  
Synthetic Routes ◽  
The Cost

Many desirable characteristics of polymers arise from the method of polymerization and structural features of their repeat units, which typically are responsible for the polymer’s performance at the cost of processability. While linear alternatives are popular, polymers composed of cyclic repeat units across their backbones have generally been shown to exhibit higher optical transparency, lower water absorption, and higher glass transition temperatures. These specifically include polymers built with either substituted alicyclic structures or aromatic rings, or both. In this review article, we highlight two useful ring-forming polymer groups, perfluorocyclobutyl (PFCB) aryl ether polymers and ortho-diynylarene- (ODA) based thermosets, both demonstrating outstanding thermal stability, chemical resistance, mechanical integrity, and improved processability. Different synthetic routes (with emphasis on ring-forming polymerization) and properties for these polymers are discussed, followed by their relevant applications in a wide range of aspects.

Studies on the ionization produced by metallic salts in flames I. The determination of the collision frequency of electrons in coal-gas/air flames

1950 ◽  
Vol 201 (1067) ◽  
pp. 480-488 ◽  
Keyword(s):  
Conversion Factor ◽  
Collision Frequency ◽  
Metal Salt ◽  
Alkali Metal Salt ◽  
Electron Content ◽  
Radio Waves ◽  
Coal Gas ◽  
Flame Ionization ◽  
Metallic Salts

As an introduction to the study of reactions contingent on ionization in flames, an experimental measurement has been made of the collision frequency of electrons with molecules in coal-gas/air flames, containing added alkali metal salt. This quantity is an important parameter in the expression relating the electron content of a flame with the attenuation of centimetric radio waves by it. This attenuation has been chosen as a convenient method of investigating flame ionization. The form of the results obtained agree well with the predictions of theory, a uniform difference of about 20 % between measured collision frequency and that calculated on a very simple gas kinetic hypothesis being obtained. A suitable conversion factor has been evolved for proceeding from attenuation of 3 cm. waves to electron concentration/cm. 3 .

Zeolates: A Coordination Chemistry View of Metal-Ligand Bonding in Intrazeolite MOCVD Type Precursors and Semiconductor Nanoclusters

1992 ◽  
Vol 277 ◽  
Author(s):  
Geoffrey A. Ozin ◽  
Carol L. Bowes ◽  
Mark R. Steele
Keyword(s):  
Self Assembly ◽  
Materials Science ◽  
Zeolite Y ◽  
Chemical Vapour ◽  
Internal Surface ◽  
Building Blocks ◽  
Structural Features ◽  
Organic Chemical ◽  
Wide Range ◽  
Shape Selective

ABSTRACTVarious MOCVD (metal-organic chemical vapour deposition) type precursors and their self-assembled semiconductor nanocluster products [1] have been investigated in zeolite Y hosts. From analysis of in situ observations (FTIR, UV-vis reflectance, Mössbauer, MAS-NMR) of the reaction sequences and structural features of the precursors and products (EXAFS and Rietveld refinement of powder XRD data) the zeolite is viewed as providing a macrospheroidal, multidendate coordination environment towards encapsulated guests. By thinking about the α- and β-cages of the zeolite Y host effectively as a zeolate ligand composed of interconnected aluminosilicate “crown ether-like” building blocks, the materials chemist is able to better understand and exploit the reactivity and coordination properties of the zeolite internal surface for the anchoring and self-assembly of a wide range of encapsulated guests. This approach helps with the design of synthetic strategies for creating novel guest-host inclusion compounds having possible applications in areas of materials science such as nonlinear optics, quantum electronics, and size/shape selective catalysis.

scholarly journals Dispersive evaluation and surface chemistry of advanced, multifunctional silica/lignin hybrid biomaterials

2013 ◽  
Vol 11 (11) ◽  
pp. 1860-1873 ◽  
Author(s):  
Magdalena Nowacka ◽  
Łukasz Klapiszewski ◽  
Małgorzata Norman ◽  
Teofil Jesionowski
Keyword(s):  
Zeta Potential ◽  
Surface Charge ◽  
Electrochemical Sensors ◽  
Relevant Information ◽  
Structural Features ◽  
Kraft Lignin ◽  
Morphological Properties ◽  
Wide Range ◽  
Hybrid Biomaterials

AbstractAdvanced silica/lignin hybrid biomaterials were obtained using hydrated or fumed silicas (Aerosil®200) and Kraft lignin as precursors, which is a cheap and biodegradable natural polymer. To extend the possible range of applications, the silicas were first modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and then with Kraft lignin, which had been oxidized with sodium periodate. The SiO2/lignin hybrids and precursors were characterised by means of determination of their physicochemical and dispersive-morphological properties. The effectiveness of silica binding to lignin was verified by FT-IR spectroscopy. The zeta potential value provides relevant information regarding interactions between colloid particles. Measurement of the zeta potential values enabled an indirect assessment of stability for the studied hybrid systems. Determination of zeta potential and density of surface charge also permitted the quantitative analysis of changes in surface charge, and indirectly confirmed the effectiveness of the proposed method for synthesis of SiO2/lignin hybrid materials. A particularly attractive feature for practical use is their stability, especially electrokinetic stability. It is expected that silica/lignin hybrids will find a wide range of applications (polymer fillers, biosorbents, electrochemical sensors), as they combine the unique properties of silica with the specific structural features of lignin. This makes these hybrids biomaterials advanced and multifunctional.

scholarly journals Novel Trifluoromethyl Pyrimidinone Compounds With Activity Against Mycobacterium tuberculosis

2021 ◽  
Vol 9 ◽  
Author(s):  
Erik Hembre ◽  
Julie V. Early ◽  
Joshua Odingo ◽  
Catherine Shelton ◽  
Olena Anoshchenko ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Major Change ◽  
Structural Features ◽  
Research Area ◽  
Biological Properties ◽  
Pyridyl Ring ◽  
Pyridyl Group ◽  
Gram Positive Bacteria ◽  
Wide Range ◽  
Cytotoxic Molecules

The identification and development of new anti-tubercular agents are a priority research area. We identified the trifluoromethyl pyrimidinone series of compounds in a whole-cell screen against Mycobacterium tuberculosis. Fifteen primary hits had minimum inhibitory concentrations (MICs) with good potency IC90 is the concentration at which M. tuberculosis growth is inhibited by 90% (IC90 &lt; 5 μM). We conducted a structure–activity relationship investigation for this series. We designed and synthesized an additional 44 molecules and tested all analogs for activity against M. tuberculosis and cytotoxicity against the HepG2 cell line. Substitution at the 5-position of the pyrimidinone with a wide range of groups, including branched and straight chain alkyl and benzyl groups, resulted in active molecules. Trifluoromethyl was the preferred group at the 6-position, but phenyl and benzyl groups were tolerated. The 2-pyridyl group was required for activity; substitution on the 5-position of the pyridyl ring was tolerated but not on the 6-position. Active molecules from the series demonstrated low selectivity, with cytotoxicity against eukaryotic cells being an issue. However, there were active and non-cytotoxic molecules; the most promising molecule had an MIC (IC90) of 4.9 μM with no cytotoxicity (IC50 &gt; 100 μM). The series was inactive against Gram-negative bacteria but showed good activity against Gram-positive bacteria and yeast. A representative molecule from this series showed rapid concentration-dependent bactericidal activity against replicating M. tuberculosis bacilli with ~4 log kill in &lt;7 days. Overall the biological properties were promising, if cytotoxicity could be reduced. There is scope for further medicinal chemistry optimization to improve the properties without major change in structural features.

Sign in / Sign up

Export Citation Format

Share Document