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ENGINEERING (1248 journals)                  1 2 3 4 5 6 7 | Last

Showing 1 - 200 of 1205 Journals sorted alphabetically
3 Biotech     Open Access   (Followers: 8)
3D Research     Hybrid Journal   (Followers: 20)
AAPG Bulletin     Hybrid Journal   (Followers: 8)
AASRI Procedia     Open Access   (Followers: 14)
Abstract and Applied Analysis     Open Access   (Followers: 3)
Aceh International Journal of Science and Technology     Open Access   (Followers: 2)
ACS Nano     Full-text available via subscription   (Followers: 275)
Acta Geotechnica     Hybrid Journal   (Followers: 7)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 7)
Acta Polytechnica : Journal of Advanced Engineering     Open Access   (Followers: 3)
Acta Scientiarum. Technology     Open Access   (Followers: 3)
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Active and Passive Electronic Components     Open Access   (Followers: 7)
Adaptive Behavior     Hybrid Journal   (Followers: 11)
Adıyaman Üniversitesi Mühendislik Bilimleri Dergisi     Open Access  
Adsorption     Hybrid Journal   (Followers: 4)
Advanced Engineering Forum     Full-text available via subscription   (Followers: 7)
Advanced Science     Open Access   (Followers: 5)
Advanced Science Focus     Free   (Followers: 5)
Advanced Science Letters     Full-text available via subscription   (Followers: 10)
Advanced Science, Engineering and Medicine     Partially Free   (Followers: 7)
Advanced Synthesis & Catalysis     Hybrid Journal   (Followers: 18)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Complex Systems     Hybrid Journal   (Followers: 7)
Advances in Engineering Software     Hybrid Journal   (Followers: 27)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Fuzzy Systems     Open Access   (Followers: 5)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 13)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 22)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Natural Sciences: Nanoscience and Nanotechnology     Open Access   (Followers: 29)
Advances in Operations Research     Open Access   (Followers: 12)
Advances in OptoElectronics     Open Access   (Followers: 5)
Advances in Physics Theories and Applications     Open Access   (Followers: 13)
Advances in Polymer Science     Hybrid Journal   (Followers: 43)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Remote Sensing     Open Access   (Followers: 44)
Advances in Science and Research (ASR)     Open Access   (Followers: 5)
Aerobiologia     Hybrid Journal   (Followers: 3)
African Journal of Science, Technology, Innovation and Development     Hybrid Journal   (Followers: 6)
AIChE Journal     Hybrid Journal   (Followers: 35)
Ain Shams Engineering Journal     Open Access   (Followers: 5)
Akademik Platform Mühendislik ve Fen Bilimleri Dergisi     Open Access   (Followers: 1)
Alexandria Engineering Journal     Open Access   (Followers: 1)
AMB Express     Open Access   (Followers: 1)
American Journal of Applied Sciences     Open Access   (Followers: 26)
American Journal of Engineering and Applied Sciences     Open Access   (Followers: 10)
American Journal of Engineering Education     Open Access   (Followers: 9)
American Journal of Environmental Engineering     Open Access   (Followers: 16)
American Journal of Industrial and Business Management     Open Access   (Followers: 23)
Analele Universitatii Ovidius Constanta - Seria Chimie     Open Access  
Annals of Combinatorics     Hybrid Journal   (Followers: 4)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of Regional Science     Hybrid Journal   (Followers: 7)
Annals of Science     Hybrid Journal   (Followers: 7)
Antarctic Science     Hybrid Journal   (Followers: 1)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applicable Analysis: An International Journal     Hybrid Journal   (Followers: 1)
Applied Catalysis A: General     Hybrid Journal   (Followers: 6)
Applied Catalysis B: Environmental     Hybrid Journal   (Followers: 18)
Applied Clay Science     Hybrid Journal   (Followers: 6)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 11)
Applied Magnetic Resonance     Hybrid Journal   (Followers: 4)
Applied Nanoscience     Open Access   (Followers: 8)
Applied Network Science     Open Access   (Followers: 3)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Physics Research     Open Access   (Followers: 5)
Applied Sciences     Open Access   (Followers: 3)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Arabian Journal for Science and Engineering     Hybrid Journal   (Followers: 5)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 5)
Archives of Foundry Engineering     Open Access  
Archives of Thermodynamics     Open Access   (Followers: 8)
Arkiv för Matematik     Hybrid Journal   (Followers: 1)
ASEE Prism     Full-text available via subscription   (Followers: 3)
Asia-Pacific Journal of Science and Technology     Open Access  
Asian Engineering Review     Open Access  
Asian Journal of Applied Science and Engineering     Open Access   (Followers: 1)
Asian Journal of Applied Sciences     Open Access   (Followers: 2)
Asian Journal of Biotechnology     Open Access   (Followers: 8)
Asian Journal of Control     Hybrid Journal  
Asian Journal of Current Engineering & Maths     Open Access  
Asian Journal of Technology Innovation     Hybrid Journal   (Followers: 8)
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
ATZagenda     Hybrid Journal  
ATZextra worldwide     Hybrid Journal  
Australasian Physical & Engineering Sciences in Medicine     Hybrid Journal   (Followers: 1)
Australian Journal of Multi-Disciplinary Engineering     Full-text available via subscription   (Followers: 2)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 9)
Avances en Ciencias e Ingeniería     Open Access  
Balkan Region Conference on Engineering and Business Education     Open Access   (Followers: 1)
Bangladesh Journal of Scientific and Industrial Research     Open Access  
Basin Research     Hybrid Journal   (Followers: 5)
Batteries     Open Access   (Followers: 6)
Bautechnik     Hybrid Journal   (Followers: 1)
Bell Labs Technical Journal     Hybrid Journal   (Followers: 26)
Beni-Suef University Journal of Basic and Applied Sciences     Open Access   (Followers: 4)
BER : Manufacturing Survey : Full Survey     Full-text available via subscription   (Followers: 1)
BER : Motor Trade Survey     Full-text available via subscription  
BER : Retail Sector Survey     Full-text available via subscription   (Followers: 1)
BER : Retail Survey : Full Survey     Full-text available via subscription   (Followers: 1)
BER : Survey of Business Conditions in Manufacturing : An Executive Summary     Full-text available via subscription   (Followers: 2)
BER : Survey of Business Conditions in Retail : An Executive Summary     Full-text available via subscription   (Followers: 3)
Beyond : Undergraduate Research Journal     Open Access  
Bhakti Persada : Jurnal Aplikasi IPTEKS     Open Access  
Bharatiya Vaigyanik evam Audyogik Anusandhan Patrika (BVAAP)     Open Access   (Followers: 1)
Biofuels Engineering     Open Access   (Followers: 1)
Biointerphases     Open Access   (Followers: 1)
Biomaterials Science     Full-text available via subscription   (Followers: 10)
Biomedical Engineering     Hybrid Journal   (Followers: 15)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering Letters     Hybrid Journal   (Followers: 5)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 21)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 37)
Biomedical Engineering: Applications, Basis and Communications     Hybrid Journal   (Followers: 5)
Biomedical Microdevices     Hybrid Journal   (Followers: 9)
Biomedical Science and Engineering     Open Access   (Followers: 4)
Biomedizinische Technik - Biomedical Engineering     Hybrid Journal  
Biomicrofluidics     Open Access   (Followers: 4)
BioNanoMaterials     Hybrid Journal   (Followers: 2)
Biotechnology Progress     Hybrid Journal   (Followers: 39)
Boletin Cientifico Tecnico INIMET     Open Access  
Botswana Journal of Technology     Full-text available via subscription   (Followers: 1)
Boundary Value Problems     Open Access   (Followers: 1)
Brazilian Journal of Science and Technology     Open Access   (Followers: 2)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 12)
Bulletin of Canadian Petroleum Geology     Full-text available via subscription   (Followers: 13)
Bulletin of Engineering Geology and the Environment     Hybrid Journal   (Followers: 14)
Bulletin of the Crimean Astrophysical Observatory     Hybrid Journal  
Cahiers, Droit, Sciences et Technologies     Open Access  
Calphad     Hybrid Journal  
Canadian Geotechnical Journal     Hybrid Journal   (Followers: 31)
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 42)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 6)
Case Studies in Thermal Engineering     Open Access   (Followers: 5)
Catalysis Communications     Hybrid Journal   (Followers: 6)
Catalysis Letters     Hybrid Journal   (Followers: 2)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 7)
Catalysis Science and Technology     Free   (Followers: 8)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysis Today     Hybrid Journal   (Followers: 7)
CEAS Space Journal     Hybrid Journal   (Followers: 2)
Cellular and Molecular Neurobiology     Hybrid Journal   (Followers: 3)
Central European Journal of Engineering     Hybrid Journal  
CFD Letters     Open Access   (Followers: 6)
Chaos : An Interdisciplinary Journal of Nonlinear Science     Hybrid Journal   (Followers: 2)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
Chinese Journal of Engineering     Open Access   (Followers: 2)
Chinese Science Bulletin     Open Access   (Followers: 1)
Ciencia e Ingenieria Neogranadina     Open Access  
Ciencia en su PC     Open Access   (Followers: 1)
Ciencias Holguin     Open Access   (Followers: 3)
CienciaUAT     Open Access   (Followers: 1)
Cientifica     Open Access  
CIRP Annals - Manufacturing Technology     Full-text available via subscription   (Followers: 11)
CIRP Journal of Manufacturing Science and Technology     Full-text available via subscription   (Followers: 13)
City, Culture and Society     Hybrid Journal   (Followers: 21)
Clay Minerals     Full-text available via subscription   (Followers: 10)
Clean Air Journal     Full-text available via subscription   (Followers: 1)
Clinical Science     Full-text available via subscription   (Followers: 9)
Coal Science and Technology     Full-text available via subscription   (Followers: 3)
Coastal Engineering     Hybrid Journal   (Followers: 11)
Coastal Engineering Journal     Hybrid Journal   (Followers: 6)
Coatings     Open Access   (Followers: 4)
Cogent Engineering     Open Access   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 4)
Color Research & Application     Hybrid Journal   (Followers: 2)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 14)
Combustion, Explosion, and Shock Waves     Hybrid Journal   (Followers: 13)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Numerical Methods in Engineering     Hybrid Journal   (Followers: 2)
Components, Packaging and Manufacturing Technology, IEEE Transactions on     Hybrid Journal   (Followers: 28)
Composite Interfaces     Hybrid Journal   (Followers: 7)
Composite Structures     Hybrid Journal   (Followers: 276)
Composites Part A : Applied Science and Manufacturing     Hybrid Journal   (Followers: 212)
Composites Part B : Engineering     Hybrid Journal   (Followers: 247)
Composites Science and Technology     Hybrid Journal   (Followers: 187)
Comptes Rendus Mécanique     Full-text available via subscription   (Followers: 2)
Computation     Open Access  
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 8)
Computer Science and Engineering     Open Access   (Followers: 19)
Computers & Geosciences     Hybrid Journal   (Followers: 31)
Computers & Mathematics with Applications     Full-text available via subscription   (Followers: 8)
Computers and Electronics in Agriculture     Hybrid Journal   (Followers: 5)
Computers and Geotechnics     Hybrid Journal   (Followers: 11)
Computing and Visualization in Science     Hybrid Journal   (Followers: 6)
Computing in Science & Engineering     Full-text available via subscription   (Followers: 33)
Conciencia Tecnologica     Open Access  
Concurrent Engineering     Hybrid Journal   (Followers: 3)
Continuum Mechanics and Thermodynamics     Hybrid Journal   (Followers: 8)
Control and Dynamic Systems     Full-text available via subscription   (Followers: 9)
Control Engineering Practice     Hybrid Journal   (Followers: 43)

        1 2 3 4 5 6 7 | Last

Journal Cover Applied Magnetic Resonance
  [SJR: 0.358]   [H-I: 34]   [4 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1613-7507 - ISSN (Online) 0937-9347
   Published by Springer-Verlag Homepage  [2350 journals]
  • Improved Quantification of Nuclear Magnetic Resonance Relaxometry Data via
           Partial Least Squares Analysis
    • Authors: Kathryn E. Washburn; Evan R. McCarney
      Pages: 429 - 464
      Abstract: Nuclear magnetic resonance relaxometry measurements are frequently used to quantify sample constituents. The standard approach for quantification involves converting the time-domain data to a distribution of characteristic times, either by fitting a fixed number of exponentials or performing an inverse Laplace transform, and then integrating the area under the peaks. We evaluated an alternative method to quantify relaxometry data. Partial least squares (PLS) analysis was applied directly to a variety of simulated time-domain relaxation data under diverse conditions to predict constituent content and results were compared to the standard analysis methods. For many situations, PLS analysis displayed superior performance for quantification than the standard analyses. The technique consistently produced better predictions at lower signal to noise. This robustness to noise makes it an appealing alternative for analysing data from applications that typically have low SNR, such as one-sided sensors, surface measurements, or well-logging. The method also enabled quantification of relaxation rates too close to be separated by an inverse Laplace transform. This capability may allow quantification to be performed using only one-dimensional relaxation data where multi-dimensional measurements were previously necessary to provide constituent separation. The method also enabled quantification of relaxometry data without the need for human interpretation or prior knowledge of what relaxation time is associated with a given constituent. These advantages make PLS analysis an appealing alternative for quantification of relaxometry data in many situations.
      PubDate: 2018-05-01
      DOI: 10.1007/s00723-018-0991-4
      Issue No: Vol. 49, No. 5 (2018)
  • Compressed-Sensing MRI Based on Adaptive Tight Frame in Gradient Domain
    • Authors: Xiaoyu Fan; Qiusheng Lian; Baoshun Shi
      Pages: 465 - 477
      Abstract: Compressed-sensing magnetic resonance imaging (CSMRI) aims to reconstruct the magnetic resonance (MR) image from highly undersampled K-space data. In order to improve the reconstruction quality of the MR image, this paper proposes a new gradient-based tight frame (TFG) learning algorithm (TFG-MRI) for CSMRI. TFG-MRI effectively integrates the tight frame learning technique and total variation into the same framework. In TFG-MRI, the inherent gradient sparsity of the MR image in gradient domain is utilized to represent the sparse prior knowledge, and the sparse priors in the horizontal and vertical gradient directions are exploited to learn adaptive tight frames for reconstructing the desired images. Particularly, we employ the l0-norm to promote the sparsity of the gradient image. The sparse representations of TFG are adapted for the horizontal and vertical gradient information of MR images. TFG-MRI can effectively help to capture edge contour structures in the gradient images, and to preserve more detail information of MR images. The experimental results demonstrate that the proposed TFG-MRI can reconstruct MR images more clearly in various sampling schemes. Compared with the existing MR image reconstruction algorithms, TFG-MRI can achieve higher accurate image reconstruction quality and better robustness to noises.
      PubDate: 2018-05-01
      DOI: 10.1007/s00723-018-0988-z
      Issue No: Vol. 49, No. 5 (2018)
  • To the Precision of Measuring Concentrations of Nitroxide Radicals in
           Polymers by EPR Technique
    • Authors: N. A. Chumakova; T. A. Ivanova; E. N. Golubeva; A. I. Kokorin
      Pages: 511 - 522
      Abstract: The precision of measuring concentrations of nirtoxide radicals in polymeric matrixes using modern electron paramagnetic resonance spectrometer is analyzed. The contributions of the radical nature and concentration, signal-to-noise ratio, and the integration procedure are tested as factors influencing on the precision of the measurement. It has shown that recording spectra with modern EPR spectrometer with possibility of computer analysis of spectra, the contribution of the integration error to the total error strongly depends on the signal-to-noise ratio. If the ratio is < 20, its contribution increases fast with the decrease of this parameter. If this ratio is ≥ 20, the input of the integration error becomes negligible, and the main contribution to the total error of concentration measurements comes from errors of the Q-factor determination, which are usually close to 8–10%.
      PubDate: 2018-05-01
      DOI: 10.1007/s00723-018-0992-3
      Issue No: Vol. 49, No. 5 (2018)
  • Simultaneous Recording of NMR Signals from Nuclei with Different
           Gyromagnetic Ratios Using Undersampling Technique
    • Authors: Nikolay V. Anisimov; Olga S. Pavlova
      Pages: 523 - 532
      Abstract: The article describes experiments on the simultaneous recording nuclear magnetic resonance signals from two nuclei with different gyromagnetic ratios—1H and 19F, 13C and 23Na. It is shown that large frequency detunings or/and low sampling rates are not an obstacle to their realization even in a relatively weak (0.5 T) field. We use undersampling technique when registering the response of the spin system. In this case, the sampling frequency is much less than the distance between the Larmor frequencies for the indicated nuclear pairs. It gives the effect of multiple aliasing. Fourier processing of the response produces a spectrum consisting of two subspectra, each of which corresponds to specific nucleus of the investigated pair. The subordination of the spectral peaks in each subspectrum is the same as the spectrum obtained by the usual way. Two variants of the radio-frequency excitation of the spin system (single and double pulse) are considered. A formula for calculating the excitation frequency and sampling rate, which ensures a rational distribution of the lines in the hybrid spectrum, is proposed.
      PubDate: 2018-05-01
      DOI: 10.1007/s00723-018-0998-x
      Issue No: Vol. 49, No. 5 (2018)
  • The Study of the Magnetic Properties of a Fe(III) Complex Solution by the
           NMR Method of “Stationary Coaxial Ampoule”
    • Authors: M. Yu. Volkov; O. A. Turanova; A. N. Turanov
      Pages: 327 - 334
      Abstract: For the first time, the nuclear magnetic resonance method of “stationary coaxial ampoule” was used to study the temperature dependence of the paramagnetic contribution of iron-containing complex molecules to the volume magnetic susceptibility of a solution of this complex. It was found that when the complex [Fe(salten)Cl] is dissolved in the chloroform/toluene mixture (1:1), this dependence obeys the Curie–Weiss law. On the basis of the obtained dependence the value of the effective spin of the Fe(III) ion was calculated with high accuracy. The obtained value of S eff for the Fe(III) ion agrees with the value found in the EPR study of the vitrified solution of this complex.
      PubDate: 2018-04-01
      DOI: 10.1007/s00723-017-0970-1
      Issue No: Vol. 49, No. 4 (2018)
  • NMR Self-diffusion Study of Amino Acid Ionic Liquids Based on
           1-Methyl-3-Octylimidazolium in Water
    • Authors: Yu. S. Chernyshev; A. S. Koneva; E. A. Safonova
      Abstract: In comparison with the conventional ionic liquids, water-miscible amino acid ionic liquids (AAILs) are considered as more biodegradable and biocompatible, less toxic, and as able to enhance the biomaterials stability. An application of some long-chain ionic liquids in catalysis, extraction, etc. requests the detailed analysis of ionic and water transport properties of their diluted aqueous solutions close to the area of its critical micelle concentration (cmc). In this work, the molecular transport properties of two 1-methyl-3-octylimidazolium-based AAILs, [C8mim][Val], and [C8mim][Leu] (with anions of l-Leucine or l-Valine), in the aqueous solutions were studied by measuring the self-diffusion coefficients and the solution’ viscosities in the temperature ranges 273–343 K at the AAIL’s concentrations below and above its cmc. The data on self-diffusion coefficients of water molecules and cations/anions of AAILs are discussed in terms of activation energies and of hydration effects. Above the cmc, the [C8mim][Val] molecules demonstrate the strengthening effect on the solvent structure, while the molecules of [C8mim][Leu] have structure-destructive effect. The results obtained for the relative dynamic viscosities show a decrease of micellar size with increasing temperature. In addition, it was found that the degrees of counterion binding for both AAILs are higher than for 1-methyl-3-octylimidazolium halides.
      PubDate: 2018-04-27
      DOI: 10.1007/s00723-018-1008-z
  • Application of a Stopped-Flow EPR Method for the Detection of Short-Lived
           Flavonoid Semiquinone Radicals Produced by Oxidation Using 15 N-Labeled
           Nitrosodisulfonate Radical (Fremy’s Salt)
    • Authors: Keiko Kuwabara; Yasuhiro Sakurai; Hodaka Sanuki; Chie Morimoto; Yong Li; Yusuke Miyake; Kenji Kanaori; Kunihiko Tajima
      Abstract: A stopped-flow-electron paramagnetic resonance (EPR) method was applied for the detection of short-lived radicals of flavonoids bearing a catechol moiety as the B-ring, such as flavonols (quercetin, fisetin, and rutin), flavanones (eriodictyol and taxifolin), flavanols (catechin and epicatechin), and flavone (luteolin). 15N-labeled sodium salt of nitrosodisulfonate (15NDS) was employed to obtain the highly resolved EPR hyperfine structure (hfs) of flavonoid-derived semiquinone radicals under stoichiometrically regulated reaction conditions in aqueous media (pH 10). The EPR hfs of these flavonoids radicals, except catechin and epicatechin, were recorded. Based on the g value and the proton hyperfine coupling constants (hfcc), these flavonoid-derived radicals were assigned to be semiquinone radicals of the catechol moiety (B-ring). For example, the observed EPR hyperfine structure (hfs) of the luteolin radical (Lut−·) was composed of four sets of doublet splitting, which could be ascribed to the three protons of the B-ring (a2′ = 0.136, a5′ = 0.102, and a6′ = 0.272 mT) and a vinyl proton of the C-ring (a3 = 0.099 mT). In addition, the characteristically small doublet splitting resolved for the fisetin anion radical (Fis−·, 0.028 mT) was assigned to the aromatic proton at the C5 carbon of the A-ring, indicating that the unpaired electron of the radials was partially delocalized onto the A-ring through the π bonds involved in the vinyl-carbonyl moiety of the C-ring. The hfcc of the methine protons at the C2 carbon of taxifolin and eriodictyol-derived radicals (Tax−· and Eri−·) was, respectively, evaluated to be 0.102 and 0.230 mT. The assignment of the proton hfcc of flavonoid-derived semiquinone radicals will be discussed in relation with the molecular structure of the C-ring.
      PubDate: 2018-04-26
      DOI: 10.1007/s00723-018-1012-3
  • Electrically Controlled Dimensionality of Magnetic Systems in Organic
    • Authors: Yuki Sakurai; Daisuke Matsumoto; Kazuhiro Marumoto
      Abstract: Electrically controlling charge density in materials using electronic device structures shows various interesting phenomena, such as electrically induced ferromagnetism and superconductivity, owing to strong charge interactions. However, electrically controlled dimensionality of magnetic systems has not yet been fully investigated. Here we report electrically controlled magnetic interactions and dimensionality of magnetic systems in organic materials from a microscopic viewpoint, which were revealed by electron spin resonance (ESR) spectroscopy using ionic liquid-gated devices. The ESR investigation demonstrated that the magnetic systems’ dimensionality of electrically accumulated charges varied from zero dimensional to two dimensional in a regioregular polymer, regioregular poly(3-hexylthiophene) (RR-P3HT), by increasing charge densities. This phenomenon is in contrast to those in a small molecule pentacene and a regiorandom polymer, regiorandom poly(3-hexylthiophene) (RRa-P3HT), where it varied from zero to three dimensional when their charge densities increased. Moreover, the formation of the complete spinless states of electrically induced charges was observed. Our investigation demonstrates the novel magnetic systems based on electrically induced charges.
      PubDate: 2018-04-25
      DOI: 10.1007/s00723-018-1005-2
  • Aggregation Behavior of Monomeric Surfactants and a Gemini Cationic
           Surfactant by NMR and Computer Simulation Data
    • Authors: M. V. Popova; D. L. Raev
      Abstract: Aggregation of decyltrimethylammonium bromide and cetyltrimethylammonium bromide (CTAB) in D2O has been studied. Spin–lattice relaxation time and self-diffusion coefficient of surfactant molecules were measured at concentrations below and above surfactant critical micelle concentration. The aggregation properties of conventional surfactant, CTAB, examined by nuclear magnetic resonance (NMR) and molecular dynamic (MD) simulation, were compared with the properties of double-tail analog, N,N,N′,N′-tetramethyl-N,N′dihexadecyl-1,4-butan di-ammonium di-bromide (BCTA). Both NMR and computer simulation methods suggest that micellization is a stepwise process and the pre-micellar aggregates take place in a solution at concentration below critical micelle concentration. According to MD simulation Gemini surfactant, BCTA, forms worm-like micelles, whereas CTAB, which may be considered as its “monomer”, forms only elongated micelles.
      PubDate: 2018-04-24
      DOI: 10.1007/s00723-018-1011-4
  • Imaging Doxorubicin Free Radical in Mice with Overhauser Enhanced MRI and
           its Tumor Suppression Effect in Mice
    • Authors: Nao Kato; Suguru Sato; Ken-ichi Yamada; Kazuhiro Ichikawa
      Abstract: In the treatment with anticancer drugs, it is important to deliver an anticancer agent to target site of the tumor at an appropriate concentration. However, it is difficult to directly measure the distribution amount of the agent and effect of anticancer drug is evaluated using its tumor suppression effect. In this study, we report an approach to visualizing an anticancer agent distribution in tumor-bearing mouse model using Overhauser enhanced magnetic resonance imaging (OMRI). The agent, doxorubicin, is one of anthracycline anticancer drugs and can form a free radical at its quinone sites and could be visualized using OMRI. After direct injection into a tumor, doxorubicin free radical was successfully imaged in tumor-bearing mouse, demonstrating practical usefulness of OMRI in the study of pharmacodynamics of free radical compounds. Imaging of antitumor agent would be potentially useful as a guidance tool for image-guided-therapy of cancer local chemotherapy.
      PubDate: 2018-04-21
      DOI: 10.1007/s00723-018-1004-3
  • Genotoxic Responses of Mitochondrial Oxygen Consumption Rate and
           Mitochondrial Semiquinone Radicals in Tumor Cells
    • Authors: Kumiko Yamamoto; Hironobu Yasui; Tomoki Bo; Tohru Yamamori; Wakako Hiraoka; Toshihide Yamasaki; Ken-ichi Yamada; Osamu Inanami
      Abstract: Our recent report demonstrated that genotoxic stimuli enhance mitochondrial energy metabolism in various tumor cell lines. However, the mitochondrial response against genotoxic stimuli has not been fully elucidated. In this study, to investigate mitochondrial functions in X-irradiated cells, the oxygen consumption rate (OCR) in human cervical adenocarcinoma HeLa cells was examined by electron spin resonance (ESR) spectroscopy with lithium 5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine. ESR oximetry demonstrated that basal respiration, ATP-linked respiration, proton leak, maximal respiration, and reserve capacity increased in HeLa cells 24 h after X-irradiation. However, a flow cytometric analysis using MitoTracker Green showed that mitochondrial mass also increased following X-irradiation. When the OCR was standardized to the mitochondria membrane mass, the radiation-induced increases in the respiratory parameters disappeared. This finding indicated that the radiation-induced increase in cellular OCR was explained by an increase in mitochondrial mass but not by the activation of mitochondrial respiratory-related enzymes. In addition, mitochondrial semiquinone radicals at g = 2.004 were detected by low-temperature (110 K) ESR spectroscopy. The ESR signal intensity of semiquinone radicals was enhanced by X-irradiation, suggesting an increase in the electron flow in the electron transport chain. These data will be important to understand the mechanism of radio-sensitization by mitochondria-targeting reagents in tumor cells.
      PubDate: 2018-04-21
      DOI: 10.1007/s00723-018-1007-0
  • Effect of NaCl Solution on Swelling Characteristics of Bentonite with
           Different Diffuse Double Layers
    • Authors: Haihao Yu; De’an Sun; You Gao
      Abstract: Soil particles generally possess negative ions, and form an electronic field nearby the particles, which results in generating diffuse double layers on the surface of the particles. There is no diffuse double layer at dry state, and it develops diffuse double layers first when wetted by solution. This paper investigates the effect of NaCl solution on swelling characteristics of bentonite with different initial water contents by performing a series of wetting tests. The wetting test results indicate that when the initial water content is less than 10%, the NaCl solution has no effect on the swelling. When the initial water content is larger than 10%, the swelling strain decreases with increase in the NaCl solution concentration. The nuclear magnetic resonance (NMR) tests on compacted bentonite specimens were performed. The test results indicate that the strongly bound water content is 10%, which is similar to that by other method. The NMR tests on full wetting specimens, whose initial water content is less than 10%, show that the NaCl solution has no effect on NMR tests results. When the initial water content is larger than 10%, the proportion of curves from the NMR tests decreases with increase in the NaCl solution concentration. The NMR tests results indicate that the swelling occurred mainly in the intra-aggregate rather than in the inter-aggregate.
      PubDate: 2018-04-20
      DOI: 10.1007/s00723-018-1009-y
  • Usage of Relative Differences of Experimental and Calculated Vicinal
    • Authors: Stanislav I. Selivanov
      Abstract: Comparison of the relative differences between the experimental and calculated values of proton–proton vicinal scalar constants obtained from nuclear magnetic resonance spectra of two structurally similar organic molecules makes it possible to increase the efficiency of using Karplus relationship for experimental detection and quantitative description of the conformational distortions in molecules under investigation. Advantages and disadvantages of the proposed approach are considered on the examples of the study of two pairs of rigid steroid molecules in solution where they are in a single conformation. These steroids have potential biological activity which is determined by their structural and conformational features. There is only one structural difference in each pair of compared steroids. The influence of small modifications such as substituent variation on the molecules spatial structure was investigated by the joint use of molecular optimization methods (semi-empirical and molecular mechanic) to determine the dihedral angles and Karplus-type equation of C.A.G. Haasnoot, F.A.A.M. de Leeuw and C.A. Altona to calculate vicinal constants in ethane fragments. It was shown that the usage of relative differences of experimental and calculated vicinal constants for conformational analysis of rigid molecules eliminates systematic errors of vicinal constant calculations. Such approach allows us to detect small distortions between conformations of comparable molecules with high accuracy, which are concluded in the differences of the corresponding dihedral angles within not more than 10°–15°. The proposed approach is a more sensitive way of studying small specific features of the spatial structure of molecules in comparison with the known methods on the basis of Karplus-type equation in which the absolute values of experimental and calculated vicinal proton–proton constants are compared.
      PubDate: 2018-04-20
      DOI: 10.1007/s00723-018-1003-4
  • Fractal Approach for 1 H-NMR Spectra Simplification and Data Processing
    • Authors: Jorge Costa Pereira; Ivana Jarak; Rui Albuquerque Carvalho
      Abstract: Nuclear magnetic resonance (NMR) is a powerful instrumental technique suited to characterize and identify organic substances, and has been successfully applied in the analysis of complex matrices such as biological and environmental samples. In a previous work, we demonstrated the ability of unsupervised contribution analysis (UCA) to process complex mixtures to identify the number of independent constituents and deconvolute mixed signals into specific signal sources. In this work, we evaluated the deconvolving ability of this algorithm to access underlying spectral information—we used UCA to estimate the number of contributing species and respective contributing sources and scores and with that information performed selective 1H-NMR signal suppression. We found that, in optimal NMR conditions, independently of signal source type, UCA allows us to correctly (a) estimate the number of independent contributions, (b) retrieve specific signal sources and (c) respective mixing information, allowing us to (d) characterize each contribution using signal sources and (e) quantify each specific contribution by means of its mixing information. This unsupervised soft-modeling method allows (f) individual contribution estimation and (g) respective removal from collected spectra, thus (h) enhancing spectra information for minor contributing species.
      PubDate: 2018-04-20
      DOI: 10.1007/s00723-018-1010-5
  • 15 N– 13 C Dipole Couplings in Smectic Mesophase of a Thermotropic
           Ionic Liquid
    • Authors: M. Cifelli; V. Domenici; V. I. Chizhik; S. V. Dvinskikh
      Abstract: Unique combination of ionic conductivity and anisotropic physical properties in ionic liquid crystals leads to new dynamic properties exploited in modern technological applications. Structural and dynamics information at atomic level for molecules and ions in mesophases can be obtained by nuclear magnetic resonance (NMR) spectroscopy through the measurements of dipole–dipole spin couplings. While 13C–1H and 15N–1H dipolar NMR spectra can be routinely acquired in samples with natural isotopic abundance, recording 15N–13C dipolar NMR spectra is challenging because of the unfavourable combination of two rare isotopes. In the present study, an approach to measure 15N–13C dipole-dipole NMR spectra in static liquid crystalline samples with natural abundance is introduced. We demonstrate that well-resolved spectra can be recorded within 10 h of experimental time using a conventional NMR probe and a moderately strong magnetic field. The technique is applied to a thermotropic smectic mesophase formed by an ionic liquid with imidazolium-based organic cation.
      PubDate: 2018-04-19
      DOI: 10.1007/s00723-018-1000-7
  • Double Electron–Electron Resonance Between Trapped Electron and Hole
           in a Semiconductor
    • Authors: Ikuko Akimoto; Takao Sekiya
      Abstract: We demonstrate the spin interactions between dispersedly trapped electrons and holes in a semiconductor using the double electron–electron resonance (DEER) method of the pulsed electron paramagnetic resonance (EPR) techniques. An aluminum-doped titanium dioxide crystal is adopted as a spin system, in which optically generated electrons and holes are trapped, to reveal EPR signals that appear close to each other at a selected crystal orientation under an external magnetic field. We used the four-pulse DEER method by applying two microwave frequencies to a microwave cavity for pumping electrons and probing holes at the optimum temperature of 32 K. The dipolar modulation in the probed signal by pumping interacting spins was successfully detected. The observed non-oscillating decay shape indicates that the detected interaction is caused by widely distributed trapped electron and hole spins over long distances. We were able to extract a spin-pair distribution function by the first derivative of a background-corrected curve, referring to a previously reported method.
      PubDate: 2018-04-07
      DOI: 10.1007/s00723-018-1002-5
  • A Fast and Convenient Way to Predict Relaxation During a
           Frequency-Selective Adiabatic Hyperbolic Secant Pulse (HS1 Sech Pulse)
    • Authors: Annalise R. Pfaff; Klaus Woelk
      Abstract: Frequency-selective inversion of magnetization is often achieved by long, low-power adiabatic RF pulses. Because these pulses can last hundreds of milliseconds, substantial relaxation of magnetization can occur during their application. Recently, a numerical model was introduced that allows an approximation of relaxation during frequency-selective adiabatic pulses for fast-tumbling small molecules in non-viscous solutions using only standard T1 and T2 relaxation times. This model is now extended to conditions in which net magnetization is not at its thermodynamic equilibrium prior to the adiabatic inversion. Simulated and experimental data reveal that the amplitude of net magnetization after an adiabatic inversion with the HS1 hyperbolic secant pulse can be approximated by a linear function of the magnetization before the pulse, depending only on T1 and T2 relaxation. The model presented here is particularly applicable to solvent-suppression sequences that utilize multiple adiabatic inversions, such as the multiple inversion-recovery nulling sequence EXCEPT. Tabulated slope and intercept values for the linear relationship are provided to facilitate a convenient optimization of pulse sequences that utilize HS1 frequency-selective adiabatic inversions.
      PubDate: 2018-02-26
      DOI: 10.1007/s00723-018-0989-y
  • Effect of Structural Disorder on Hydrodynamic Behavior of Alpha-Casein
           According to PFG NMR Spectroscopy
    • Authors: A. M. Kusova; A. E. Sitnitsky; Yu. F. Zuev
      Abstract: The concentration dependences of self-diffusion coefficient for intrinsically disordered milk protein αS-casein were studied by pulsed field gradient nuclear magnetic resonance. The experimental data were analyzed in a view of phenomenological approach based on the frictional formalism of non-equilibrium thermodynamics by Vink. The results of αS-CN hydrodynamic study showed that at low- and high-protein concentrations, αS-CN exists in the different structural forms. At low concentrations in the rather broad concentration range, protein remains monomeric but with greater hydrodynamic size than have rigid globular proteins of the equal mass. At high concentrations beyond the definite protein content, αS-CN tends to form associates. The application of the Vink’s approach to αS-CN testifies that the role of flexible domains in the process of self-diffusion is mainly in increasing the friction of between αS-CN molecules due to their inter-entanglement. The latter physically means that when αS-CN molecules cling each other by their flexible domains, this phenomenon provides much more efficient friction than their interaction with solvent molecules.
      PubDate: 2018-02-19
      DOI: 10.1007/s00723-018-0990-5
  • Secondary-Phase Formation in Spinel-Type LiMn 2 O 4 -Cathode Materials for
           Lithium-Ion Batteries: Quantifying Trace Amounts of Li 2 MnO 3 by Electron
           Paramagnetic Resonance Spectroscopy
    • Authors: Ruoheng Sun; Peter Jakes; Svitlana Eurich; Désirée van Holt; Shuo Yang; Melanie Homberger; Ulrich Simon; Hans Kungl; Rüdiger-A. Eichel
      Abstract: Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li2MnO3 usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li2MnO3 lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li2MnO3 below 10−2 wt.% in the synthesized products. The results reveal that the formation of Li2MnO3 secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li1+xMn2−xO4 materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels.
      PubDate: 2018-02-13
      DOI: 10.1007/s00723-018-0983-4
  • Spin Dynamics of (Sc $$_{1-x}$$ 1 - x Lu $$_{x}$$ x ) $$_{3.1}$$ 3.1 In
           Studied by Electron Spin Resonance
    • Authors: Archie Cable; Eteri Svanidze; Jessica Santiago; Emilia Morosan; Jörg Sichelschmidt
      Abstract: The electron spin resonance (ESR) of conduction electrons is reported for the weak itinerant ferromagnet Sc \(_{3.1}\) In which, upon chemical substitution with Lu, shows a suppression of ferromagnetic correlations. A well-defined ESR lineshape of Dysonian type characterizes the spectra. The ESR linewidth, determined by the spin dynamics, displays a broad minimum only for the Sc \(_{3.1}\) In compound. We discuss the results using the mechanism of exchange enhancement of spin-lifetimes.
      PubDate: 2018-02-13
      DOI: 10.1007/s00723-018-0987-0
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