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Letteratura scientifica selezionata sul tema "Coupled two-dimensional HPLC systems"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 20 febbraio 2023

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Articoli di riviste sul tema "Coupled two-dimensional HPLC systems"

Kirby, Jason, William Maher, Michael Ellwood e Frank Krikowa. "Arsenic Species Determination in Biological Tissues by HPLC - ICP - MS and HPLC - HG - ICP - MS". Australian Journal of Chemistry 57, n. 10 (2004): 957. http://dx.doi.org/10.1071/ch04094.

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The use of high-pressure liquid chromatography coupled directly or by a hydride generation system to an inductively coupled plasma mass spectrometer for the unambiguous measurement of 13 arsenic species in marine biological extracts is described. The use of two chromatography systems; a Supelcosil LC-SCX cation-exchange column eluted with a 20 mM pyridine mobile phase adjusted to pH 2.2 and 2.6 with formic acid, with a flow rate of 1.5 mL min−1 at 40°C, and a Hamilton PRP-X100 anion-exchange column eluted with 20 mM NH4H2PO4 buffer at pH 5.6, with a flow rate of 1.5 mL min−1 at 40°C, was required to separate and quantify cation and anion arsenic species. Under these conditions, arsenous acid could not be separated from other arsenic species and required the use of an additional hydride generation step. Arsenic species concentrations in a locally available Tasmanian kelp (Durvillea potatorum), a certified reference material (DORM-2), and a range of commercially available macroalgae supplements and sushi seaweeds have been measured and are provided for use as in-house quality control samples to assess the effectiveness of sample preparation, extraction, and measurement techniques.

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Pinho, Carina, Zita E. Martins, Catarina Petisca, Agata M. Figurska, Olívia Pinho e Isabel M. P. L. V. O. Ferreira. "Size exclusion and reversed-phase high-performance liquid chromatography/UV for routine control of thermal processing of cows' and donkey milk major proteins". Journal of Dairy Research 79, n. 2 (16 marzo 2012): 224–31. http://dx.doi.org/10.1017/s0022029912000064.

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Cows' and donkey milks (raw and thermally processed) and respective whey were analysed for quantification of major proteins. Two different chromatographic approaches, size exclusion (SE-HPLC) and reversed-phase high performance liquid chromatography (RP-HPLC) both coupled to UV detection were used. Usefulness of these methods for routine control of the effect of thermal processing was evaluated. The external standard method was used to calibrate the SE-HPLC and RP-HPLC systems. Concerning quantification of β-lactoglobulin (β-lg), α-lactalbumin (α-la), lysozyme (lys), and total casein (cn), no significant differences between results obtained by SE-HPLC and by RP-HPLC (t-test, P>0·05) were observed for raw milks and whey. Heating of cows' milk promoted aggregation of denatured proteins as observed by SE-HPLC, whereas α-la and β-lg from donkey milk were stable to thermal processing at 100°C (5 min). Lys was quantified in donkey raw milk and whey however, in thermally processed donkey milk lys was denatured and could not be quantified by HPLC.

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Veizerová, L., J. Piešťanský, K. Maráková, J. Galba, D. Rauová, S. Dokupilová, E. Havránek e P. Mikuš. "Comparison of column-coupled electrophoresis with liquid chromatography methods in food analysis of quinine". Acta Facultatis Pharmaceuticae Universitatis Comenianae 59, n. 1 (1 gennaio 2012): 67–80. http://dx.doi.org/10.2478/v10219-012-0011-y.

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Comparison of column-coupled electrophoresis with liquid chromatography methods in food analysis of quinineComparison of column-coupled electrophoresis with liquid chromatography methods in food analysis of quinine (QUI) is presented in this work. The capillary isotachophoresis (CITP) on-line coupled with capillary zone electrophoresis (CZE) and hyphenated with fibre-based spectrophotometric diode array detection (DAD) was compared with, (i) high performance liquid chromatography (HPLC) method with DAD detection, and (ii) HPLC method with fluorescence detection (FD). These methods were compared through their performance parameters and determined concentrations of QUI in beverages. The concentrations of QUI in two selected bitter drinks determined by the CITP-CZE-DAD method were in a good accordance with the HPLC-DAD and HPLC-FD methods. In addition, the electrophoretic method, as well as the chromatographic methods, was able to separate potential QUI related impurities from the QUI peak. The CITP-CZE-DAD method provided excellent performance parameters that were comparable (precision, accuracy, LOD, robustness) or even better (separation efficiency) than those ones provided by the chromatographic methods. Moreover, the effectivity of the electrophoresis method was higher when considering cost of analysis (equipment, consumption of separation systems), environmental aspects (organicvs. aqueous solvents), on-line sample pretreatment (CITP preconcentration and sample clean-up suitable also for the more complex matrices). Considering these findings, CITP-CZE-DAD was approved as a routine automatized method for the highly reliable quality food control.

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Fang, Lei, Hua Zhang, Jie Zhou, Yanling Geng e Xiao Wang. "Rapid Screening and Preparative Isolation of Antioxidants fromAlpinia officinarumHance Using HSCCC Coupled with DPPH-HPLC Assay and Evaluation of Their Antioxidant Activities". Journal of Analytical Methods in Chemistry 2018 (2018): 1–6. http://dx.doi.org/10.1155/2018/3158293.

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An efficient method using high-speed counter-current chromatography (HSCCC) coupled with DPPH-HPLC assay has been developed for rapid screening and preparative isolation of antioxidants from ethyl acetate fraction ofAlpinia officinarumHance. Target-guided by DPPH-HPLC assay, two antioxidants, galangin and kaempferide, were targeted and further separated with purities of 99.3% and 98.5% by HSCCC using petroleum ether–ethyl acetate–methanol–water (0.8 : 1 : 1 : 0.8,v/v) as the solvent system. The antioxidant activities of galangin and kaempferide were further evaluated by measuring their inhibiting effects on superoxide anion radical, hydroxyl radical, and hydrogen peroxide in different luminol chemiluminescence (CL) systems. As a result, galangin and kaempferide both showed potent antioxidant activities. Results of the present study indicated that the combinative method by offline coupling DPPH-HPLC and HSCCC could be widely applied for rapid screening and isolation of antioxidants from complex TCM extract.

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Pan, Ru, Dejia Shao, Xueyong Qi, Yun Wu, Wenyan Fu, Yanru Ge e Haizhen Fu. "Extraction of trace tilmicosin in real water samples using ionic liquid-based aqueous two-phase systems". Water Science and Technology 67, n. 8 (1 aprile 2013): 1671–77. http://dx.doi.org/10.2166/wst.2013.015.

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The effective method of ionic liquid-based aqueous two-phase extraction, which involves ionic liquid (IL) (1-butyl-3-methyllimidazolium chloride, [C4mim]Cl) and inorganic salt (K2HPO4) coupled with high-performance liquid chromatography (HPLC), has been used to extract trace tilmicosin in real water samples which were passed through a 0.45 μm filter. The effects of the different types of salts, the concentration of K2HPO4 and of ILs, the pH value and temperature of the systems on the extraction efficiencies have all been investigated. Under the optimum conditions, the average extraction efficiency is up to 95.8%. This method was feasible when applied to the analysis of tilmicosin in real water samples within the range 0.5–40 μg mL−1. The limit of detection was found to be 0.05 μg mL−1. The recovery rate of tilmicosin was 92.0–99.0% from the real water samples by the proposed method. This process is suggested to have important applications for the extraction of tilmicosin.

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Hafner, Verena, David Czock, Jürgen Burhenne, Klaus-Dieter Riedel, Jürgen Bommer, Gerd Mikus, Christoph Machleidt, Thomas Weinreich e Walter E. Haefeli. "Pharmacokinetics of Sulfobutylether-Beta-Cyclodextrin and Voriconazole in Patients with End-Stage Renal Failure during Treatment with Two Hemodialysis Systems and Hemodiafiltration". Antimicrobial Agents and Chemotherapy 54, n. 6 (5 aprile 2010): 2596–602. http://dx.doi.org/10.1128/aac.01540-09.

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ABSTRACT Sulfobutylether-beta-cyclodextrin (SBECD), a large cyclic oligosaccharide that is used to solubilize voriconazole (VRC) for intravenous administration, is eliminated mainly by renal excretion. The pharmacokinetics of SBECD and voriconazole in patients undergoing extracorporeal renal replacement therapies are not well defined. We performed a three-period randomized crossover study of 15 patients with end-stage renal failure during 6-hour treatment with Genius dialysis, standard hemodialysis, or hemodiafiltration using a high-flux polysulfone membrane. At the start of renal replacement therapy, the patients received a single 2-h infusion of voriconazole (4 mg per kg of body weight) solubilized with SBECD. SBECD, voriconazole, and voriconazole-N-oxide concentrations were quantified in plasma and dialysate samples by high-performance liquid chromatography (HPLC) and by HPLC coupled to tandem mass spectrometry (LC-MS-MS) and analyzed by noncompartmental methods. Nonparametric repeated-measures analysis of variance (ANOVA) was used to analyze differences between treatment phases. SBECD and voriconazole recoveries in dialysate samples were 67% and 10% of the administered doses. SBECD concentrations declined with a half-life ranging from 2.6 ± 0.6 h (Genius dialysis) to 2.4 ± 0.9 h (hemodialysis) and 2.0 ± 0.6 h (hemodiafiltration) (P < 0.01 for Genius dialysis versus hemodiafiltration). Prediction of steady-state conditions indicated that even with daily hemodialysis, SBECD will still exceed SBECD exposure of patients with normal renal function by a factor of 6.2. SBECD was effectively eliminated during 6 h of renal replacement therapy by all methods, using high-flux polysulfone membranes, whereas elimination of voriconazole was quantitatively insignificant. The SBECD half-life during renal replacement therapy was nearly normalized, but the average SBECD exposure during repeated administration is expected to be still increased.

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Rugină, Dumitriţa, Zoriţa Diaconeasa, Cristina Coman, Andrea Bunea, Carmen Socaciu e Adela Pintea. "Chokeberry Anthocyanin Extract as Pancreaticβ-Cell Protectors in Two Models of Induced Oxidative Stress". Oxidative Medicine and Cellular Longevity 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/429075.

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The aim of this study was to investigate the protective effects of a chokeberry anthocyanin extract (CAE) on pancreaticβ-cells (βTC3) exposed to hydrogen peroxide- (H2O2-) and high glucose- (HG-) induced oxidative stress conditions. In order to quantify individual anthocyanins high performance liquid chromatography (HPLC) coupled to photodiode array (PDA) was used. The identification of the fragment ion pattern of anthocyanins was carried out by electrospray ionization mass spectrometry (LC-ESI-MS). The results showed that physiologically achievable concentrations of CAE (1, 5, and 10 μM) protectβTC3 against H2O2- and HG-induced cytotoxicity. Antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were increased in pancreaticβ-cells pretreated with CAE compared to cells exposed to the prooxidant agents. GSH levels initially reduced after exposure to H2O2and HG were restored by pretreatment with CAE. Insulin secretion inβTC3 cells was enhanced by CAE pretreatment. CAE restored the insulin pool and diminished the intracellular reactive oxygen species level in glucose-induced stress condition inβTC3 cells. These results demonstrate that anthocyanins from CAE were biologically active, showing a secretagogue potential and an antioxidative protection of enzymatic systems, conferring protection against H2O2and glucose toxicity inβTC3 cells.

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Wu, Zhisheng, Xinyuan Shi, Na Zhao, Yanling Pei, Manfei Xu, Luwei Zhou, Yang Li e Yanjiang Qiao. "Estimation of multivariate detection limits of four quality parameters in licorice using MEMS–NIR spectrometry coupled with two sampling accessories". Journal of Innovative Optical Health Sciences 08, n. 05 (21 agosto 2015): 1550009. http://dx.doi.org/10.1142/s1793545815500091.

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In this work, multivariate detection limits (MDL) estimator was obtained based on the micro-electro-mechanical systems–near infrared (MEMS–NIR) technology coupled with two sampling accessories to assess the detection capability of four quality parameters (glycyrrhizic acid, liquiritin, liquiritigenin and isoliquiritin) in licorice from different geographical regions. 112 licorice samples were divided into two parts (calibration set and prediction set) using Kennard–Stone (KS) method. Four quality parameters were measured using high-performance liquid chromatography (HPLC) method according to Chinese pharmacopoeia and previous studies. The MEMS–NIR spectra were acquired from fiber optic probe (FOP) and integrating sphere, then the partial least squares (PLS) model was obtained using the optimum processing method. Chemometrics indicators have been utilized to assess the PLS model performance. Model assessment using chemometrics indicators is based on relative mean prediction error of all concentration levels, which indicated relatively low sensitivity for low-content analytes (below 1000 parts per million (ppm)). Therefore, MDL estimator was introduced with alpha error and beta error based on good prediction characteristic of low concentration levels. The result suggested that MEMS–NIR technology coupled with fiber optic probe (FOP) and integrating sphere was able to detect minor analytes. The result further demonstrated that integrating sphere mode (i.e., MDL0.05,0.05, 0.22%) was more robust than FOP mode (i.e., MDL0.05,0.05, 0.48%). In conclusion, this research proposed that MDL method was helpful to determine the detection capabilities of low-content analytes using MEMS–NIR technology and successful to compare two sampling accessories.

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Katsa, Maria, Natalia Papalouka, Theodora Mavrogianni, Irene Papagiannopoulou, Marios Kostakis, Charalampos Proestos e Nikolaos S. Thomaidis. "Comparative Study for the Determination of Fat-Soluble Vitamins in Rice Cereal Baby Foods Using HPLC-DAD and UHPLC-APCI-MS/MS". Foods 10, n. 3 (18 marzo 2021): 648. http://dx.doi.org/10.3390/foods10030648.

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Two liquid chromatographic systems, one coupled to atmospheric pressure chemical ionization and tandem mass spectrometric methods (UHPLC-APCI-MS/MS) and the other a high-performance liquid chromatographic coupled to diode array detector (HPLC-DAD) were used to develop and validate methods for the simultaneous determination of fat-soluble vitamins A, D3 and E in rice cereal baby foods. The chromatographic separation was performed on C18 columns with a mixture of methanol-acetonitrile as mobile phase for all methods. The extraction of fat-soluble vitamins included enzymatic hydrolysis with α-amylase, saponification, extraction with petroleum ether or n-hexane and purification with silica cartridge (only for vitamin D3). Quantification of vitamin D3 and E through UHPLC-APCI-MS/MS was performed by the use of internal standards (IS) D3-d3 and E-d6, respectively, while IS was not used for vitamin A. The methods were optimized and validated in terms of linearity, precision, trueness, limits of detection and quantification. The recoveries were in the range of 85.0–107% for retinol, 92.0–105% for α-tocopherol and 95.2–106% for cholecalciferol and the %RSD (Relative Standard Deviation) values ranged from 6.4% to 15%. The evaluation of the methods was also conducted through the estimation of uncertainties, the application in commercial samples and the participation in a proficiency test

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Carail, Michel, e Catherine Caris-Veyrat. "Carotenoid oxidation products: From villain to saviour?" Pure and Applied Chemistry 78, n. 8 (1 gennaio 2006): 1493–503. http://dx.doi.org/10.1351/pac200678081493.

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Carotenoid oxidation products have various structures, among which epoxides and apo- or seco-carotenoids are the two main families. Although both these compound types are widely found in the natural world, the sensitivity of carotenoids to oxidation means they can also be an unwanted presence in in vitro assays. On the other hand, carotenoid oxidation products have also provided chemists with useful chemical tools for the structural identification of carotenoids, and in the natural world they are important biological mediators for plants and animals. In vitro, carotenoid oxidation products have been found to exert various effects which are either potentially beneficial or, on the contrary, detrimental to human health. However, to date, few carotenoid oxidation products have been found in humans. In order to isolate and characterize carotenoid oxidation products and identify their mechanism of formation, we set up two chemical oxidation systems. Lycopene was oxidized with potassium permanganate in a biphasic system to produce the fullest possible range of apo-lycopenals and some diapocarotene-dials. Biomimetic chemical systems of a heminic enzyme center were shown to oxidize lycopene and β-carotene into different families of molecules. Analysis by high-performance liquid chromatography coupled with a diode array-UV/vis detector and a mass spectrometry detector (HPLC-DAD-MS) was used to gain insight into the possible mechanisms of formation of the carotenoid oxidation products formed by these biomimetic systems.

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Più fonti

Tesi sul tema "Coupled two-dimensional HPLC systems"

Sweeney, Alan Peter, University of Western Sydney, of Science Technology and Environment College e of Science Food and Horticulture School. "Studies toward the development of two dimensional high performance liquid chromatographic systems for the separation of complex samples". THESIS_CSTE_SFH_Sweeney_A.xml, 2002. http://handle.uws.edu.au:8081/1959.7/630.

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Coupled two-dimensional HPLC systems were developed for the separation of complex sample matrices. Low molecular weight polystyrene oligomers were used as model compounds for the development of these systems since the sample dimensionality of oligostyrenes could be defined and classified according to two sample characteristics. That is, oligostyrenes could be classed as a two-dimensional sample, where one sample dimension is the variation in the number of monomers that make up oligomeric units determining the weight of the polymer, with a second sample dimension being the variation in stereoisomerism of each oligomer. During this study it was found that by combining two separation dimensions consisting of C18 and carbon clad zirconia (CCZ) phases separation of oligostyrenes according to molecular weight and stereochemistry was possible in coupled two-dimensional systems. The C18 phase separated the sample according to molecular weight, while the CCZ phase separated the sample according to the stereochemistry. The stereoisomer separations of the oligostyrenes reported on the CCZ surface were far superior to those previously reported in the literature. The efficiency of the separation process in a coupled two-dimensional system was then evaluated by studying the variation in band variance of a test probe. The results of the study indicated that the performance of a two-dimensional separation process was highly dependent upon the mobile phase compatibility, even when solvents were completely miscible and of similar polarities. Extracts from 17 species of Australian native plants were examined for xanthine oxidase inhibitory activity, the enzyme responsible for the formation of the disease gout. Chromatographic separation was conducted on plant extracts found to possess significant inhibitory activity against xanthine oxidase, with an extract from the species Clerodendrum floribundum R. Br. found to possess the greatest activity of the species examined. A two-dimensional separation of a crude extract from Clerodendrum floribundum R. Br. was conducted using one of the developed HPLC systems, to illustrate the use of such a system for the separation of a non-model complex sample mixture
Doctor of Philosophy (PhD)

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Castleton, I. M. "Electron transport in coupled one- and two-dimensional systems". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597365.

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In this dissertation, transport measurements are presented on the coupling between two closely separated two-dimensional electron gases (2DEGs) formed within GaAs/AlGaAs heterostructures. The experiments fall into three main areas. Firstly, the electrical properties of a new type of switching transistor are investigated. A 2DEG is formed at the inverted and non-inverted heterojunction of a wide GaAs/AlGaAs quantum well. With the use of front and back gates, charge is moved from one 2DEG to the other in a manner similar to that proposed theoretically in the Velocity Modulated Transistor (VMT) device concept. In the VMT, switching is obtained through a mobility modulation rather than through a more conventional carrier density modulation, thereby minimising capacitive time delays. By adjusting the grown-in carrier density and mobility of each 2DEG, successful VMT operation is demonstrated, and a mobility modulation of a factor of 125 is achieved. In the second part, the resistance resonance in strongly coupled double 2DEGs is investigated. The size of the resistance resonance in three samples is measured as a function of the 2DEG mobility ratio, and the results are compared with predictions made by classical and quantum transport theories. Quenching of the resistance resonance by an in-plane magnetic field is observed, and the low- and high-field magnetoresistance are explained by considering the field-induced distortions of the Fermi surface. Finally, the transport properties of structures containing double quasi-1D wires are studied. The wires are formed by laterally confining two 2DEGs using a single Schottky split-gate. Ballistic quantisation in units of 2e²/h and 4e²/h is observed in widely spaced, non-interacting wires, while closely spaced wires are used to investigate the effects of wavefunction hybridisation in reduced dimensionality. Variations in the screening of a single quasi-1D wire are revealed by compressibility measurements.

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Tölle, Sebastian [Verfasser], e Ulrich [Akademischer Betreuer] Eckern. "Spin-charge coupled transport in two- and three-dimensional Rashba systems / Sebastian Tölle ; Betreuer: Ulrich Eckern". Augsburg : Universität Augsburg, 2018. http://d-nb.info/1170582974/34.

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Tölle, Sebastian Verfasser], e Ulrich [Akademischer Betreuer] [Eckern. "Spin-charge coupled transport in two- and three-dimensional Rashba systems / Sebastian Tölle ; Betreuer: Ulrich Eckern". Augsburg : Universität Augsburg, 2018. http://d-nb.info/1170582974/34.

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Lynass, Mark Ronald. "Novel physics in two dimensional charge carrier structures : anisotropc magneto-transport at Landau-level crossings in aluminium arsenide quantum wells and coupled two dimensional electron and hole systems". Thesis, University of Bath, 2006. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428382.

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Jooß, Kevin [Verfasser], Philippe [Akademischer Betreuer] Schmitt-Kopplin, Bernhard [Gutachter] Küster, Philippe [Gutachter] Schmitt-Kopplin e Gerhard [Gutachter] Scriba. "Development and application of two-dimensional separation systems coupled to mass spectrometry incorporating capillary electrophoresis / Kevin Jooß ; Gutachter: Bernhard Küster, Philippe Schmitt-Kopplin, Gerhard Scriba ; Betreuer: Philippe Schmitt-Kopplin". München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1200098501/34.

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Shah, Umer. "Novel RF MEMS Devices Enabled by Three-Dimensional Micromachining". Doctoral thesis, KTH, Mikro- och nanosystemteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-143757.

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This thesis presents novel radio frequency microelectromechanical (RF MEMS) circuits based on the three-dimensional (3-D) micromachined coplanar transmission lines whose geometry is re-configured by integrated microelectromechanical actuators. Two types of novel RF MEMS devices are proposed. The first is a concept of MEMS capacitors tuneable in multiple discrete and well-defined steps, implemented by in-plane moving of the ground side-walls of a 3-D micromachined coplanar waveguide transmission line. The MEMS actuators are completely embedded in the ground layer of the transmission line, and fabricated using a single-mask silicon-on-insulator (SOI) RF MEMS fabrication process. The resulting device achieves low insertion loss, a very high quality factor, high reliability, high linearity and high self actuation robustness. The second type introduces two novel concepts of area efficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. The coupling is achieved by tuning both the ground and the signal line coupling, obtaining a large tuneable coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity over a very large bandwidth. This thesis also presents for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. Closed-form analytical formulas for the IIP3 of MEMS multi-device circuit concepts are derived. A nonlinearity analysis, based on these formulas and on measured device parameters, is performed for different circuit concepts and compared to the simulation results of multi-device conlinear electromechanical circuit models. The degradation of the overall circuit nonlinearity with increasing number of device stages is investigated. Design rules are presented so that the mechanical parameters and thus the IIP3 of the individual device stages can be optimized to achieve a highest overall IIP3 for the whole circuit.The thesis further investigates un-patterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip inductances. The approach used is to increase the thickness of the ferromagnetic material without increasing its conductivity, by using multilayer NiFe and AlN sandwich structure. This suppresses the induced currents very effectively and at the same time increases the ferromagnetic resonance, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. The so far highest permeability values above 1 GHz for on-chip integrated un-patterned NiFe layers were achieved.

QC 20140328

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Sweeney, Alan P. "Studies toward the development of two dimensional high performance liquid chromatographic systems for the separation of complex samples". Thesis, 2002. http://handle.uws.edu.au:8081/1959.7/630.

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Milroy, Coleen S. "Development of two-dimensional liquid chromatographic systems for the optimised separation and targeted isolation of complex samples". Thesis, 2010. http://handle.uws.edu.au:8081/1959.7/496071.

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Chromatography is a powerful separation technique that was initially developed for the isolation of natural components in a highly purified form from complex mixtures. However, early applications of chromatography that were preparative in nature were quickly surpassed by analytical separations as the need for qualitative and quantitative information about components present in simple and complex mixtures became the primary objective. HPLC is the commonly used analytical separation technique for the determination of components in complex mixtures as it offers high sensitivity and also high selectivity. In general, HPLC is carried out in a single dimension using one primary retention mechanism dictated largely by the stationary phase. Although modern HPLC column technology has made available stationary phases with improved efficiency, particularly for the separations of complex mixtures, there are limits to its use. In reality there is only so much space available for components in a given sample to be separated into individual peaks, which is limited by the peak width and determined by the efficiency of the column. This is highly dependent upon the number of theoretical plates (N) available for the separation and therefore the peak capacity. Multidimensional HPLC is a technique that is gaining appreciable support at the analytical level due to the vastly expanded separation space that allows for increased resolution of components in complex samples. The introduction of a second dimension, which offers a change in selectivity to that of the first dimension, is a means of increasing the total peak capacity of the separation process and therefore expanding the separation space. Two-dimensional HPLC is an effective separation technique for the analysis of complex mixtures if the sample’s complexity can be reduced as the separation mechanism of the first dimension may be tailored towards the sample’s multidimensionality and/or its physical characteristics such as size, polarity, charge and shape. Reducing the complexity can be as simple as ensuring co-elution of the key components in the first dimension, but then utilising the second dimension to resolve those components co-eluting in the first dimension. Here the first dimension can be considered essentially as a ‘clean-up’ step in order to isolate the required targets in the second dimension. This essentially reduces the required peak capacity of the first dimension and the separation space in the second dimension more than compensates for this reduction as the second dimension is required to separate a lower number of components. Preparative HPLC has only seen resurgence in the last few decades with traditional methods such as distillation, centrifugal extraction and crystallisation unsuitable for the problems encountered by the various industries. The stringent regulations of governing bodies for the approval of highly purified products to be released into a highly competitive market dictate largely the advancement of chromatographic methods for preparative separations. Chapter 1 is a general introduction with a brief history of chromatography presented. The theory and practice of two-dimensional chromatographic separations and preparative chromatographic separations are also discussed. Sample dimensionality and its importance to the determination of orthogonality of separation steps are also considered. Chapter 2 details the chemicals and equipment used to perform the experiments outlined throughout the thesis. Specific general methods are also included here for reference. Chapter 3 describes a model framework for the development of a two-dimensional liquid chromatographic system and was reliant on low molecular weight oligostyrenes as they are complex, are indefinitely stable and easily characterised. The ultra high resolution separation of diastereomers of low molecular weight oligostyrenes on carbon adsorption stationary phases are also discussed. Chapter 4 examines the practical aspects in the optimisation of targeted isolations in two-dimensional HPLC with emphasis on analytical scale analysis. The emphasis in this chapter was on the isolation of “a‟ target analyte from “a‟ complex mixture, where effectively ‘a’ represents a generic sample, complex in nature. Chapter 4 also examines the practical aspects in the optimisation of targeted isolations in two-dimensional HPLC with emphasis on analytical scale analysis. However this chapter focuses on maximising the recovery of the target component at analytical scale analysis. Chapter 5 investigates the practical aspects in the optimisation of preparative scale two-dimensional isolations by the establishment of a continuous batch-wise 2D purification process, with the intent to preparative scale-up. In this chapter the experimental variables that effect the production of a target component are introduced and the influences they have on the separation are discussed. Chapter 5 also investigates the use of the system introduced at the preparative level however high sample loads are now used to determine the effect of the recovery in both the first and second dimensions; the purity of the collected product; and finally the product recovery yield, effective production rate and the practical production rate. Chapter 6 focuses on improving the quality of the isolation process by increasing the peak capacity of the second dimension firstly, followed by an increase in the peak capacity in both the first and second dimensions. This improved the resolution and therefore reduced the number of components transferred to the second dimension. This had the benefit of decreasing the performance demand of the second dimension column. Chapter 7 summarises all of the findings contained throughout this thesis.

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Norris, Ryan Christopher. "Silicon-Integrated Two-Dimensional Phononic Band Gap Quasi-Crystal Architecture". Thesis, 2011. http://hdl.handle.net/10012/6279.

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The development and fabrication of silicon-based phononic band gap crystals has been gaining interest since phononic band gap crystals have implications in fundamental science and display the potential for application in engineering by providing a relatively new platform for the realization of sensors and signal processing elements. The seminal study of phononic band gap phenomenon for classical elastic wave localization in structures with periodicity in two- or three-physical dimensions occurred in the early 1990’s. Micro-integration of silicon devices that leverage this phenomenon followed from the mid-2000’s until the present. The reported micro-integration relies on exotic piezoelectric transduction, phononic band gap crystals that are etched into semi-infinite or finite-thickness slabs which support surface or slab waves, phononic band gap crystals of numerous lattice constants in dimension and phononic band gap crystal truncation by homogeneous mediums or piezoelectric transducers. The thesis reports, to the best of the author's knowledge, for the first time, the theory, design methodology and experiment of an electrostatically actuated silicon-plate phononic band gap quasi-crystal architecture, which may serve as a platform for the development of a new generation of silicon-integrated sensors, signal processing elements and improved mechanical systems. Electrostatic actuation mitigates the utilization of piezoelectric transducers and provides action at a distance type forces so that the phononic band gap quasi-crystal edges may be free standing for potentially reduced anchor and substrate mode loss and improved energy confinement compared with traditional surface and slab wave phononic band gap crystals. The proposed phononic band gap quasi-crystal architecture is physically scaled for fabrication as MEMS in a silicon-on-insulator process. Reasonable experimental verification of the model of the electrostatically actuated phononic band gap quasi-crystal architecture is obtained through extensive dynamic harmonic analysis and mode shape topography measurements utilizing optical non-destructive laser-Doppler velocimetry. We have utilized our devices to obtain fundamental information regarding novel transduction mechanisms and behavioral characteristics of the phononic band gap quasi-crystal architecture. Applicability of the phononic band gap quasi-crystal architecture to physical temperature sensors is demonstrated experimentally. Vibration stabilized resonators are demonstrated numerically.

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Libri sul tema "Coupled two-dimensional HPLC systems"

Bertel, E., e A. Menzel. Nanostructured surfaces: Dimensionally constrained electrons and correlation. A cura di A. V. Narlikar e Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533046.013.11.

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This article examines dimensionally constrained electrons and electronic correlation in nanostructured surfaces. Correlation effects play an important role in spatial confinement of electrons by nanostructures. The effect of correlation will become increasingly dominant as the dimensionality of the electron wavefunction is reduced. This article focuses on quasi-one-dimensional (quasi-1D) confinement, i.e. more or less strongly coupled one-dimensional nanostructures, with occasional reference to 2D and 0D systems. It first explains how correlated systems exhibit a variety of electronically driven phase transitions, and especially the phases occurring in the generic phase diagram of correlated materials. It then describes electron–electron and electron–phonon interactions in low-dimensional systems and the phase diagram of real quasi-1D systems. Two case studies are considered: metal chains on silicon surfaces and quasi-1D structures on metallic surfaces. The article shows that spontaneous symmetry breaking occurs for many quasi-1D systems on both semiconductor and metal surfaces at low temperature.

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Capitoli di libri sul tema "Coupled two-dimensional HPLC systems"

Jancovici, Bernard. "Two-Dimensional Logarithmic Interaction on Curved Surfaces". In Strongly Coupled Coulomb Systems, 709–12. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/0-306-47086-1_134.

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You, Yuncheng. "Global Attractor of a Coupled Two-Cell Brusselator Model". In Infinite Dimensional Dynamical Systems, 319–52. New York, NY: Springer New York, 2012. http://dx.doi.org/10.1007/978-1-4614-4523-4_13.

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Willett, Roger D. "EPR in Two-Dimensional Exchange Coupled Systems". In Magneto-Structural Correlations in Exchange Coupled Systems, 269–96. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-6511-9_10.

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Reynolds, M. A., B. D. Fried e G. J. Morales. "Velocity-Space Drag and Diffusion in Model, Two-Dimensional Plasma". In Strongly Coupled Coulomb Systems, 591–95. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/0-306-47086-1_110.

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Ghazali, A., e A. Gold. "Screened Interaction Potential and Bound States between Two Negative Charged Particles in the Three- and Two-Dimensional Electron Gas". In Strongly Coupled Coulomb Systems, 439–44. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/0-306-47086-1_79.

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Khveshchenko, D. V. "Interacting Electrons in Strong Magnetic Fields: A Genuine Example of a Two-Dimensional Non-Fermi-Liquid". In Strongly Coupled Coulomb Systems, 487–91. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/0-306-47086-1_88.

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Mou, Xuehao, Leonard Franklin Register e Sanjay Kumar Banerjee. "Ultralow-Power Pseudospintronic Devices via Exciton Condensation in Coupled Two-Dimensional Material Systems". In Nanoscale Materials and Devices for Electronics, Photonics and Solar Energy, 31–91. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-18633-7_2.

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JANCOVICI, Bernard. "TWO-DIMENSIONAL COULOMB SYSTEMS: SOLVABLE MODELS AT Γ = 2". In Strongly Coupled Plasma Physics, 285–96. Elsevier, 1990. http://dx.doi.org/10.1016/b978-1-4832-2908-9.50039-1.

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JANCOVICI, Bernard. "TWO-DIMENSIONAL COULOMB SYSTEMS: SOLVABLE MODELS AT Γ = 2". In Strongly Coupled Plasma Physics, 285–96. Elsevier, 1990. http://dx.doi.org/10.1016/b978-0-444-88363-6.50039-x.

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Joubert, Gerhard, e Anthony Maeder. "Four Decades of Cluster Computing". In Parallel Computing: Technology Trends. IOS Press, 2020. http://dx.doi.org/10.3233/apc200017.

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During the latter half of the 1970s high performance computers (HPC) were constructed using specially designed and manufactured hardware. The preferred architectures were vector or array processors, as these allowed for high speed processing of a large class of scientific/engineering applications. Due to the high cost of the development and construction of such HPC systems, the number of available installations was limited. Researchers often had to apply for compute time on such systems and wait for weeks before being allowed access. Cheaper and more accessible HPC systems were thus in great need. The concept to construct high performance parallel computers with distributed Multiple Instruction Multiple Data (MIMD) architectures using standard off-the-shelf hardware promised the construction of affordable supercomputers. Considerable scepticism existed at the time about the feasibility that MIMD systems could offer significant increases in processing speeds. The reasons for this were due to Amdahl’s Law, coupled with the overheads resulting from slow communication between nodes and the complex scheduling and synchronisation of parallel tasks. In order to investigate the potential of MIMD systems constructed with existing off-the-shelf hardware a first simple two processor system was constructed that finally became operational in 1979. In this paper aspects of this system and some of the results achieved are reviewed.

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Atti di convegni sul tema "Coupled two-dimensional HPLC systems"

Byrdwell, William, e Hari Kiran Kotapati. "Adventures in multiple dimensions of chromatography and mass spectrometry for lipidomic analysis". In 2022 AOCS Annual Meeting & Expo. American Oil Chemists' Society (AOCS), 2022. http://dx.doi.org/10.21748/athx8798.

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Two-dimensional liquid chromatography (2D-LC) is commercially available and has become increasingly common in laboratories across the world. Most 2D-LC systems that are coupled to mass spectrometry use one mass spectrometer attached to the outlet of the second dimension, and the first dimension is reconstructed by “stitching together” the signal from all of the modulation periods. This requires short, fast separations in the second dimension, and fast-scanning mass spectrometers, otherwise “under sampling” can occur. Quantification is problematic using the “blobs” in 2D-LC chromatograms. We have bypassed or eliminated many of the shortcomings or limitations in conventional systems by using multiple mass spectrometers distributed across two or three dimensions of chromatography. We have published results showing the use of split-flow 2D-LC with four mass spectrometers in LC1MS2 × LC1MS2 = LC2MS4 experiments that combined non-aqueous reversed-phase (NARP) HPLC with silver ion chromatography UHPLC for analysis of cis/trans isomers and regioisomers in seed oils, with classic quantification of fat-soluble vitamins (FSVs) and triacylglycerols (TAGs) using direct detection in the first dimension and isomer separation in the second dimension. We have further reported split-flow three-dimensional (3D) LC with four mass spectrometers in LC1MS2 × (LC1MS1 + LC1MS1) = LC3MS4 analysis of infant formula that combined classic quantification of FSVs in the first dimension and TAG quantification by lipidomic analysis in the second dimension. We innovated multi-cycle (a.k.a., “constructive wraparound”) chromatography in the second second dimension for improved separation compared to the conventional approach used in the first second dimension. These and other combinations of LCxMSy are described.

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Vepa, Kameswara S., Diederik Van Nuffel, Wim Van Paepegem e Joris Degrieck. "Fully Coupled Time Domain Modelling of 3D Floating Bodies and Mooring Systems in Regular and Irregular Sea States". In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-83464.

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Research on floating bodies like Wave Energy Converters (WECs) and Laser Imaging Detection And Ranging (LIDAR) systems has recently known a large growth. To study the minute details of the working model, it is important to study the effect of interactions between the waves, floating bodies and the mooring systems that are controlling the motion of the floating body. To achieve a more realistic numerical model in the time domain, a number of programs are linked together. The idea is to use the strength of each individual program for better results and also reduce the computational time. This paper provides a solution in the direction of using a fully coupled time domain coupling code that controls the data flow between a fluid solver, a structural solver, and a kinematic system simulator. Two- and three-dimensional fully coupled models are studied for calculation times and accuracy of results, and scaling is tested through parallelization on a large HPC cluster. The time step size of the whole model can be controlled by the user. Calculation times and memory requirements vary largely based on the factors like: domain size, SPH particle size, material model used for the floating body and the mooring system, complexity of the mechanical system inside the floating body. As a test case, a rigid body model is presented in this paper.

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Romano, Raffaele, e Domenico D'Alessandro. "Incoherent control and entanglement for two-dimensional coupled systems". In Defense and Security Symposium, a cura di Eric J. Donkor, Andrew R. Pirich e Howard E. Brandt. SPIE, 2006. http://dx.doi.org/10.1117/12.664735.

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Xie, Wei-Chau. "Vibration Mode Localization in Randomly Disordered Weakly Coupled Two-Dimensional Systems". In ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-3953.

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Abstract In this paper, a general method of regular perturbation for linear eigenvalue problems is presented, in which the orders of perturbation terms are extended to infinity. The method of regular perturbation is applied to study vibration mode localization in randomly disordered weakly coupled two-dimensional cantilever-spring arrays. Localization factors, which characterize the average exponential rates of decay or growth of the amplitudes of vibration, are defined in terms of the angles of orientation. First-order approximate results of the localization factors are obtained using a combined analytical-numerical approach. For the systems under consideration, the direction in which vibration is originated corresponds to the smallest localization factor; whereas the “diagonal” directions correspond to the largest rate of decay or growth of the amplitudes of vibration. When plotted in the logarithmic scale, the vibration modes are of a hill shape with the amplitudes of vibration decaying linearly away from the cantilever at which vibration is originated.

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Errando-Herranz, Carlos, Eva Schöll, Raphael Picard, Micaela Laini, Samuel Gyger, Ali W. Elshaari, Artur Branny et al. "On-chip single photon emission from a waveguide-coupled two-dimensional semiconductor". In Quantum Nanophotonic Materials, Devices, and Systems 2020, a cura di Mario Agio, Cesare Soci e Matthew T. Sheldon. SPIE, 2020. http://dx.doi.org/10.1117/12.2567240.

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Korotky, Steven K. "Three-dimensional representation of phase-mismatch switching in coupled two-state systems". In Integrated and Guided Wave Optics. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/igwo.1986.faa5.

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Coupled single-mode optical waveguides with adjustable phase-mismatch are a key component in many electrooptic devices. Here we introduce and present key results for a three-space representation of the transfer characteristics of optical circuits employing coupling and phase-mismatch between waveguides. This approach permits an intuitive understanding of the operation of devices, such as the directional coupler and Mach-Zehnder switches, the Δβ-reversal coupler, optical combiners, and polarization transformers. As such, the method is conducive to innovative device design. A novel class of switch has been identified using this formalism and has been demonstrated experimentally.

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Umezawa, Toshimasa, e Naokatsu Yamamoto. "Crosstalk analysis in high speed two-dimensional photodetector array directly coupled to multicore fibers". In Integrated Optics: Design, Devices, Systems and Applications, a cura di Pavel Cheben, Jiří Čtyroký e Iñigo Molina-Fernández. SPIE, 2019. http://dx.doi.org/10.1117/12.2520407.

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Delpero, Tommaso, Paolo Ermanni, Filippo Casadei, Massimo Ruzzene e Andrea Bergamini. "Experimental Characterization of Two-Dimensional Tunable Metamaterials". In ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/smasis2012-8087.

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A periodic array of shunted piezoelectric patches is used to produce a two-dimensional metamaterial with tunable properties. The proposed configuration exploits the waveguiding capabilities of a phononic crystal plate in conjunction with a periodic arrangement of eight surface-bonded PZT disks. Each piezo transducer is connected to an independent resistive-inductive network, so that the system features an internal resonance that occurs at the tuning frequency of the shunting circuits. The dispersion relations of the resulting metamaterial are experimentally estimated through detailed mappings of the wavefield measured using a scanning laser doppler vibrometer. Experimental results indicate that the coupled system features a band structure behavior induced by the internal resonance of the electrical networks, and suggest the possibility to alter the waveguiding properties of the considered metamaterial without modifying the physical structure of the phononic crystal plate.

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Fedorovich, G., D. Kornovan e M. Petrov. "Disorder in one-dimensional array of two-level systems coupled to a waveguiding mode". In INTERNATIONAL CONFERENCE ON PHYSICS AND CHEMISTRY OF COMBUSTION AND PROCESSES IN EXTREME ENVIRONMENTS (COMPHYSCHEM’20-21) and VI INTERNATIONAL SUMMER SCHOOL “MODERN QUANTUM CHEMISTRY METHODS IN APPLICATIONS”. AIP Publishing, 2020. http://dx.doi.org/10.1063/5.0032487.

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Yang, Zhaojie, Yi Fang, Guojun Han, Lingjun Kong e Guohua Zhang. "Design and Analysis of Spatially Coupled Protograph LDPC Codes for Two-Dimensional Magnetic Recording Systems". In 2018 Asia Pacific Magnetic Recording Conference (APMRC). IEEE, 2018. http://dx.doi.org/10.1109/apmrc.2018.8601100.

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