Bibliographies thématiques / DFRT

Sommaire

Articles de revues
Thèses
Livres
Chapitres de livres
Actes de conférences
Rapports d'organisations

Littérature scientifique sur le sujet « DFRT »

Auteur : Grafiati

Publié le 29 mars 2025

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres

Choisissez une source :

Consultez les listes thématiques d’articles de revues, de livres, de thèses, de rapports de conférences et d’autres sources académiques sur le sujet « DFRT ».

À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.

Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.

Articles de revues sur le sujet "DFRT"

Caspers, Patrick, Luc Bury, Bérangère Gaucher, Jutta Heim, Stuart Shapiro, Sibylle Siegrist, Anne Schmitt-Hoffmann, Laure Thenoz et Heinrich Urwyler. « In Vitro and In Vivo Properties of Dihydrophthalazine Antifolates, a Novel Family of Antibacterial Drugs ». Antimicrobial Agents and Chemotherapy 53, n^o 9 (22 juin 2009) : 3620–27. http://dx.doi.org/10.1128/aac.00377-09.

Texte intégral

Résumé :

ABSTRACT Racemic 2,4-diaminopyrimidine dihydrophthalazine derivatives BAL0030543, BAL0030544, and BAL0030545 exhibited low in vitro MICs toward small, selected panels of Enterococcus faecalis, Enterococcus faecium, Streptococcus pneumoniae, Moraxella catarrhalis, and Mycobacterium avium, though the compounds were less active against Haemophilus influenzae. The constellation of dihydrofolate reductases (DHFRs) present in 20 enterococci and 40 staphylococci was analyzed and correlated with the antibacterial activities of the dihydrophthalazines and trimethoprim. DHFRs encoded by dfrB, dfrA (S1 isozyme), dfrE, and folA were susceptible to the dihydrophthalazines, whereas DHFRs encoded by dfrG (S3 isozyme) and dfrF were not. Studies with the separated enantiomers of BAL0030543, BAL0030544, and BAL0030545 revealed preferential inhibition of susceptible DHFRs by the (R)-enantiomers. BAL0030543, BAL0030544, and BAL0030545 were well tolerated by mice during 5- and 10-day oral toxicity studies at doses of up to 400 mg/kg of body weight. Using a nonoptimized formulation, the dihydrophthalazines displayed acceptable oral bioavailabilities in mice, and efficacy studies with a septicemia model of mice infected with trimethoprim-resistant, methicillin-resistant Staphylococcus aureus gave 50% effective dose values in the range of 1.6 to 6.25 mg/kg.

Styles APA, Harvard, Vancouver, ISO, etc.

Hamid, Aabid, Atul Anand et Ram Kinkar Roy. « The charge transfer limit of a chemical adduct : the role of perturbation on external potential ». Physical Chemistry Chemical Physics 19, n^o 17 (2017) : 10905–12. http://dx.doi.org/10.1039/c7cp01208j.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Liu, Li, et Ji Chun Tan. « Multiple Watermarks Embedding Simultaneously to Identify Image Status Based on Fractional Fourier Transform ». Advanced Materials Research 341-342 (septembre 2011) : 758–62. http://dx.doi.org/10.4028/www.scientific.net/amr.341-342.758.

Texte intégral

Résumé :

A new method of multiple watermarks embedding simultaneously to identify image status based on once and twice discrete fractional Fourier transform (DFRT) is presented. Random series watermark, chirp watermark and annotation watermark are embedded simultaneously in fractional Fourier transform domain to identify digital tamper detection, scanning detection, duplicate detection. According to the extracting situation of three kinds of watermarks from an image and the twice DFRT amplitude spectrum, we can know whether the image is tampered, scanned or duplicated. It provides a convenient way to identify the status of the image and will be an all-sided and comprehensive anti-counterfeiting technology.

Styles APA, Harvard, Vancouver, ISO, etc.

Saha, Bapan, et Pradip Kr Bhattacharyya. « Understanding reactivity, aromaticity and absorption spectra of carbon cluster mimic to graphene : a DFT study ». RSC Advances 6, n^o 83 (2016) : 79768–80. http://dx.doi.org/10.1039/c6ra15016k.

Texte intégral

Résumé :

Effect of doping B and/or N on the reactivity, aromaticity and absorption spectra of graphene and functionalized (–OH and –COOH) carbon cluster mimicking graphene is studied using DFT, DFRT and TD-DFT.

Styles APA, Harvard, Vancouver, ISO, etc.

Shishido, E., S. Higashijima, Y. Emori et K. Saigo. « Two FGF-receptor homologues of Drosophila : one is expressed in mesodermal primordium in early embryos ». Development 117, n^o 2 (1 février 1993) : 751–61. http://dx.doi.org/10.1242/dev.117.2.751.

Texte intégral

Résumé :

The fibroblast growth factor (FGF)/receptor system is thought to mediate various developmental events in vertebrates. We examined molecular structures and expression of DFR1 and DFR2, two Drosophila genes closely related to vertebrate FGF-receptor genes. DFR1 and DFR2 proteins contain two and five immunoglobulin-like domains, respectively, in the extracellular region, and a split tyrosine kinase domain in the intracellular region. In early embryos, DFR1 RNA expression, requiring both twist and snail proteins, is specific to mesodermal primordium and invaginated mesodermal cells. At later stages, putative muscle precursor cells and cells in the central nervous system (CNS) express DFR1. DFR2 expression occurs in endodermal precursor cells, CNS midline cells and certain ectodermal cells such as those of trachea and salivary duct. FGF-receptor homologues in Drosophila would thus appear essential for generation of mesodermal and endodermal layers, invaginations of various types of cells, and CNS formation.

Styles APA, Harvard, Vancouver, ISO, etc.

Choudhary, Nancy, et Boas Pucker. « Conserved amino acid residues and gene expression patterns associated with the substrate preferences of the competing enzymes FLS and DFR ». PLOS ONE 19, n^o 8 (28 août 2024) : e0305837. http://dx.doi.org/10.1371/journal.pone.0305837.

Texte intégral

Résumé :

Background Flavonoids, an important class of specialized metabolites, are synthesized from phenylalanine and present in almost all plant species. Different branches of flavonoid biosynthesis lead to products like flavones, flavonols, anthocyanins, and proanthocyanidins. Dihydroflavonols form the branching point towards the production of non-colored flavonols via flavonol synthase (FLS) and colored anthocyanins via dihydroflavonol 4-reductase (DFR). Despite the wealth of publicly accessible data, there remains a gap in understanding the mechanisms that mitigate competition between FLS and DFR for the shared substrate, dihydroflavonols. Results An angiosperm-wide comparison of FLS and DFR sequences revealed the amino acids at positions associated with the substrate specificity in both enzymes. A global analysis of the phylogenetic distribution of these amino acid residues revealed that monocots generally possess FLS with Y132 (FLSY) and DFR with N133 (DFRN). In contrast, dicots generally possess FLSH and DFRN, DFRD, and DFRA. DFRA, which restricts substrate preference to dihydrokaempferol, previously believed to be unique to strawberry species, is found to be more widespread in angiosperms and has evolved independently multiple times. Generally, angiosperm FLS appears to prefer dihydrokaempferol, whereas DFR appears to favor dihydroquercetin or dihydromyricetin. Moreover, in the FLS-DFR competition, the dominance of one over the other is observed, with typically only one gene being expressed at any given time. Conclusion This study illustrates how almost mutually exclusive gene expression and substrate-preference determining residues could mitigate competition between FLS and DFR, delineates the evolution of these enzymes, and provides insights into mechanisms directing the metabolic flux of the flavonoid biosynthesis, with potential implications for ornamental plants and molecular breeding strategies.

Styles APA, Harvard, Vancouver, ISO, etc.

Gibreel, Amera, et Ola Sköld. « High-Level Resistance to Trimethoprim in Clinical Isolates of Campylobacter jejuni by Acquisition of Foreign Genes (dfr1 and dfr9) Expressing Drug-Insensitive Dihydrofolate Reductases ». Antimicrobial Agents and Chemotherapy 42, n^o 12 (1 décembre 1998) : 3059–64. http://dx.doi.org/10.1128/aac.42.12.3059.

Texte intégral

Résumé :

ABSTRACT The pathogenic bacterium Campylobacter jejuni has been regarded as endogenously resistant to trimethoprim. The genetic basis of this resistance was characterized in two collections of clinical isolates of C. jejuni obtained from two different parts of Sweden. The majority of these isolates were found to carry foreigndfr genes coding for resistant variants of the dihydrofolate reductase enzyme, the target of trimethoprim. The resistance genes, found on the chromosome, were dfr1 anddfr9. In about 10% of the strains, the dfr1and dfr9 genes occurred simultaneously. About 10% of the examined isolates were found to be negative for these dfrgenes and showed a markedly lower trimethoprim resistance level than the other isolates. The dfr9 and dfr1 genes were located in the context of remnants of a transposon and an integron, respectively. Two different surroundings for thedfr9 gene were characterized. One was identical to the right-hand end of the transposon Tn5393, and in the other, the dfr9 gene was flanked by only a few nucleotides of a Tn5393 sequence. The insertion of the dfr9 gene into the C. jejuni chromosome could have been mediated by Tn5393. The frequent occurrence of high-level trimethoprim resistance in clinical isolates of C. jejuni could be related to the heavy exposure of food animals to antibacterial drugs, which could lead to the acquisition of foreign resistance genes in naturally transformable strains of C. jejuni.

Styles APA, Harvard, Vancouver, ISO, etc.

Hamza, Rafik, Alzubair Hassan, Teng Huang, Lishan Ke et Hongyang Yan. « An Efficient Cryptosystem for Video Surveillance in the Internet of Things Environment ». Complexity 2019 (9 décembre 2019) : 1–11. http://dx.doi.org/10.1155/2019/1625678.

Texte intégral

Résumé :

Surveillance systems paradigm envisions the pervasive interconnection and cooperation of interactive devices over the Internet infrastructure. Nevertheless, dissemination and processing of surveillance video amid the Internet of Things (IoT) applications become a susceptible issue due to the large volume and the significant information of these data. Moreover, surveillance devices on IoT have very limited resources such as memory and storage. The actual security methods are not quite appropriate for surveillance IoT systems. Thus, a particular cryptosystem technique is required for surveillance data security. In this paper, we propose an efficient cryptosystem to secure IoT-based surveillance systems. The proposed cryptosystem framework contains three parts. First, a lightweight automatic summarization technique based on a fast histogram-clustering approach is used to extract the keyframes from the surveillance video. Then, we employ a discrete cosine transform (DCT) technique to compress the extracted data size. Finally, the proposed framework performs an efficient image encryption algorithm by employing a discrete fractional random transform (DFRT). The testing results and analysis confirm the features of the proposed cryptosystem on surveillance systems. The proposed framework is fast and ensures secure and efficient real-time processing by minimizing the transmission cost and storage.

Styles APA, Harvard, Vancouver, ISO, etc.

Liu, Xifeng, Wen Yuan, Chaokang Gu, Wenhao Huang et Weixin Hu. « Nature of Sigma-Type Lithium Bonding Interaction in Nanoscale ». Nano LIFE 04, n^o 04 (décembre 2014) : 1441020. http://dx.doi.org/10.1142/s1793984414410207.

Texte intégral

Résumé :

Li-based rechargeable batteries are becoming popular power sources for biomedical devices and healthcare equipment. In nanoscale, lithium bonds may associate with intermolecular noncovalent interactions when Li atoms are shared by adjacent atoms inside rechargeable Li batteries. Theoretical study of lithium boding interactions thus is of paramount importance for a better understanding of the working mechanisms and designing high-efficient electrode–electrolyte interfaces from nanolevel for Li-based batteries. In this study, we used state-of-the-art theoretical methods, with inclusion of density functional theory/symmetry-adapted perturbation theory (DFT/SAPT), density functional reactivity theory (DFRT) and energy decomposition analysis (EDA), to delve into the nature of lithium bonding interactions. Our results showed that B3LYP outperforms all other functionals under consideration in the conventional supramolecular scheme, indicating that the formation of a lithium bond is not dispersion-driven. The calculated PBE0/SAPT and B3LYP/EDA data are consistent with each other, unravelling that the lithium bond is mainly of an electrostatically driven nature. Both steric hindrance and exchange-correlation potentials also make important contributions when two-variable fitting is considered. These results provide new sight in understanding lithium atom interactions for potential lithium-based batteries applications.

Styles APA, Harvard, Vancouver, ISO, etc.

Bergmann, René, Mark van der Linden, Gursharan S. Chhatwal et D. Patric Nitsche-Schmitz. « Factors That Cause Trimethoprim Resistance in Streptococcus pyogenes ». Antimicrobial Agents and Chemotherapy 58, n^o 4 (3 février 2014) : 2281–88. http://dx.doi.org/10.1128/aac.02282-13.

Texte intégral

Résumé :

ABSTRACTThe use of trimethoprim in treatment ofStreptococcus pyogenesinfections has long been discouraged because it has been widely believed that this pathogen is resistant to this antibiotic. To gain more insight into the extent and molecular basis of trimethoprim resistance inS. pyogenes, we tested isolates from India and Germany and sought the factors that conferred the resistance. Resistant isolates were identified in tests for trimethoprim or trimethoprim-sulfamethoxazole (SXT) susceptibility. Resistant isolates were screened for the known horizontally transferable trimethoprim-insensitive dihydrofolate reductase (dfr) genesdfrG,dfrF,dfrA,dfrD, anddfrK. The nucleotide sequence of the intrinsicdfrgene was determined for resistant isolates lacking the horizontally transferable genes. Based on tentative criteria, 69 out of 268 isolates (25.7%) from India were resistant to trimethoprim. Occurring in 42 of the 69 resistant isolates (60.9%),dfrFappeared more frequently thandfrG(23 isolates; 33.3%) in India. ThedfrFgene was also present in a collection of SXT-resistant isolates from Germany, in which it was the only detected trimethoprim resistance factor. ThedfrFgene caused resistance in 4 out of 5 trimethoprim-resistant isolates from the German collection. An amino acid substitution in the intrinsic dihydrofolate reductase known from trimethoprim-resistantStreptococcus pneumoniaeconferred resistance toS. pyogenesisolates ofemmtype 102.2, which lacked other aforementioneddfrgenes. Trimethoprim may be more useful in treatment ofS. pyogenesinfections than previously thought. However, the factors described herein may lead to the rapid development and spread of resistance ofS. pyogenesto this antibiotic agent.

Styles APA, Harvard, Vancouver, ISO, etc.

Plus de sources

Thèses sur le sujet "DFRT"

Valloire, Hugo. « Développements de modes avancés de microscopie à force piézoélectrique pour films minces piézoélectriques et ferroélectriques ». Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY063.

Texte intégral

Résumé :

De nombreuses applications actuelles dans le secteur de la microélectronique reposent sur l’utilisation de matériaux piézoélectriques et ferroélectriques sous forme de films minces. Par exemple, des dispositifs MEMS incluant les capteurs, actionneurs et convertisseurs d'énergie tirent profit des propriétés piézoélectriques des matériaux. Par ailleurs, l'émergence de nombreux sujets de recherche a fait suite à la découverte du potentiel de certains de ces matériaux pour les dispositifs microélectroniques. C’est par exemple le cas de l'utilisation du HfO2 pour ses propriétés ferroélectriques dans les mémoires non volatiles FeRAM et FeFET. Dans ce contexte, diverses techniques de dépôt de films minces de matériaux piézoélectriques et ferroélectriques sont actuellement en cours d'optimisation. Les méthodes de caractérisation spécifiques à ces matériaux sont essentielles pour évaluer la qualité de leur élaboration et pour approfondir la compréhension des phénomènes physiques sous-jacents, ce qui est crucial pour leur intégration dans des dispositifs microélectroniques avancés.C’est dans ce cadre que s’inscrit cette thèse, dont l’objectif est de développer des techniques de caractérisation des propriétés piézoélectriques et ferroélectriques de dispositifs élaborés sous forme de films minces, à l’échelle nanométrique. La microscopie à force piézoélectrique permet de telles analyses, mais est sensible à de nombreux artefacts, tels que les effets électrostatiques, qui peuvent significativement influencer les résultats. L'objectif de cette thèse est de développer, mettre en œuvre et coupler de nouvelles techniques avancées basées sur la microscopie à force piézoélectrique pour minimiser les artefacts de mesure en dissociant leur contribution de celle des effets piézoélectriques et ferroélectriques, et pour caractériser un éventail plus large de propriétés des matériaux. C’est par exemple le cas du mode couplé de microscopie à force piézoélectrique en spectroscopie de commutation avec suivi de résonance à double fréquence, développé pour la première fois durant cette thèse, permettant de maximiser le rapport signal sur bruit tout en réduisant et mesurant l'influence de divers artefacts. De plus, il permet de mesurer la variation des propriétés du matériau sous l'influence d'un champ électrique, reflétant ainsi des conditions d'utilisation plus réalistes. Ce mode a été étendu pour des mesures de cartographie permettant également de déterminer la variation des propriétés mesurées sur la surface du matériau à l’échelle nanométrique. Le développement d'un ensemble de programmes informatiques a joué un rôle clé dans l'élaboration de ces nouveaux modes, depuis le pilotage des équipements jusqu'à l'analyse avancée des mesures
Many current applications in the microelectronics sector rely on the use of piezoelectric and ferroelectric materials in the form of thin films. For instance, MEMS devices, including sensors, actuators, and energy harvesters, take advantage of the piezoelectric properties of materials. Moreover, the discovery of the potential of certain materials for microelectronic devices has spurred significant research, as exemplified by the use of HfO2 for its ferroelectric properties in non-volatile memories like FeRAM and FeFET. In this context, various deposition techniques for piezoelectric and ferroelectric thin films are currently under optimization. Specific characterization methods for these materials are essential to evaluate the quality of their fabrication and to enhance the understanding of the underlying physical phenomena, which is critical for their integration into advanced microelectronic devices.This thesis aims to develop characterization techniques for the piezoelectric and ferroelectric properties of devices fabricated as thin films at the nanoscale. Piezoelectric force microscopy enables such analyses but is susceptible to numerous artifacts, such as electrostatic effects, which can significantly impact the results. The objective of this thesis is to develop, implement, and combine new advanced techniques based on PFM to minimize measurement artifacts by separating their contributions from those of piezoelectric and ferroelectric effects, and to characterize a wider range of material properties. For instance, the coupled PFM mode in switching spectroscopy with dual-frequency resonance tracking, developed for the first time in this thesis, maximizes the signal-to-noise ratio while reducing and measuring the influence of various artifacts. Furthermore, this mode allows the measurement of material property variations under the influence of an electric field, thus reflecting more realistic operating conditions. This mode has been extended for mapping measurements, allowing the determination of variations in the measured properties across the material surface at the nanoscale. The development of a suite of software programs played a key role in the creation of these new modes, from equipment control to advanced data analysis

Styles APA, Harvard, Vancouver, ISO, etc.

Boonchun, Adisak. « First-Principles Calculation of Defect Energies in ZnO and Related Materials ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1310056351.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Ma, Weiliang. « Etude des propriétés électroniques, de transport et topologiques des composés du système n(PbTe)-m(Bi2Te3) par des méthodes de premier principe ». Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0615.

Texte intégral

Résumé :

Du fait d’une faible conductivité thermique, les composés de la série homologue n(PbTe)-m(Bi2Te3) ont été reportés dans la littérature comme de bons thermoélectriques. Dans ces chalcogénures présentant une structure cristalline en couches, deux types d’empilement, nommés A et B, ont été mis en évidence pour le composé Pb2Bi2Te5. De façon à comprendre les différences existantes entre les propriétés de ces empilements, nous avons déterminé les propriétés électroniques et thermoélectriques du composé Pb2Bi2Te5 dans chacun des empilements en réalisant des calculs et analysé la densité électronique de ces structures en utilisant la théorie quantique des atomes dans les molécules. Les modules élastiques, les constantes diélectriques, les charges effectives de Born et la dispersion des phonons ont été calculés et à partir de ces résultats, la conductivité thermique a été déterminée en résolvant l’équation de transport de Boltzmann. De façon à obtenir un ensemble complet de propriétés thermoélectriques et expliquer la faible conductivité thermique observée dans ces composés, une étude théorique complète des structures électroniques, des propriétés de transport et des propriétés dynamiques de réseau de quatre composés (PbTe, Bi2Te3, PbBi2Te4 and PbBi4Te7) a été réalisée. La conductivité thermique κ_l a été évaluée en calculant les constantes de forces interatomiques du second et du troisième ordre. L’ingénierie de bandes a été mise sur différents composés de la série (Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5), en appliquant des contraintes biaxiales en compression et en tension, de façon à améliorer leurs propriétés thermoélectriques
Owing to their low lattice thermal conductivity, compounds of the n(PbTe)-m(Bi2Te3) homologous series have been reported in the literature with good thermoelectric properties. Among these layered chalcogenides, the Pb2Bi2Te5 compound has been evidenced with two stacking sequences termed A and B. In order to understand the differences in their properties, we have determined the electronic and the thermoelectric properties of the Pb2Bi2Te5 compound with the two different stacking sequences from a series of first principles calculations using density functional theory and analysed the electronic density of these compounds by using the quantum theory of atoms in molecules. The elastic moduli, dielectric constants, Born effective charges, and phonon dispersion within the quasi-harmonic approximation have also been calculated and based on these calculations results, the thermal conductivity has been determined by solving the Boltzmann transport equation. In order to get a comprehensive set of thermoelectric properties and explain the low lattice thermal conductivity observed in these compounds, a full theoretical study of the electronic structures, transport behaviour, and lattice dynamic properties of four chalcogenides compounds (PbTe, Bi2Te3, PbBi2Te4 and PbBi4Te7) has been performed. The lattice thermal conductivity κ_l has been evaluated by calculating the second- and third-order interatomic force constants. The band engineering approach has then been implemented by applying biaxial tensile and compressive strains on various compounds of this series, namely Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5 in order to improve their TE properties

Styles APA, Harvard, Vancouver, ISO, etc.

Kerber, Torsten. « Dispersionskorrekturen von DFT für Festkörperprobleme ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16634.

Texte intégral

Résumé :

In der vorliegenden Arbeit wird die Korrektur weitreichender Dispersionswechselwirkungen fuer Dichtefunktionaltheorie fuer Rechnungen unter Anwendung periodischer Randbedingungen erweitert. Am Beispiel des Graphit wird der Einfluss der Dispersionskorrektur auf Strukturparameter und Energien gezeigt. Die berechneten Werte fuer Schichtabstand und Wechselwirkungsenergie stimmen sehr gut mit experimentell bestimmten Daten ueberein. Anhand von Clusterstudien wird gezeigt, dass die Dispersionskorrektur nur sehr langsam mit der Systemgroesse konvergiert. Die genaue Beschreibung der Dispersionswechselwirkungen zwischen Graphitschichten mit der PBE+D-Methode ist nur bei Anwendung periodischer Randbedingungen oder durch eingebettete Clustermodelle moeglich. Der Vergleich der PBE+D- mit der genauen, aber sehr aufwendigen [MP2:PBE + delta-CCSD(T)]-Methode zeigt, dass die strukturellen Unterschiede zwischen beiden Methoden gering sind. Die berechneten Reaktionsenergien unterscheiden sich hingegen deutlich. Die neu entwickelte, effiziente [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode ergaenzt die PBE+D-Energie um zwei Korrekturterme. Der erste Term, die delta-MP2-Korrektur, behebt die Ueberstabilisierung polarer Strukturen (PBE) mit einer MP2-Rechnung am Basissatzlimit. Der zweite Term ueberprueft die delta-MP2-Korrektur durch eine CCSD(T)-Rechnung fuer einen kleinen Cluster. Die [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode wird fuer die Reaktion von C4H8-Kohlenwasserstoffen mit H-Ferrierit angewendet. In der Zeolithpore wurden pi-Komplexe, Butylkationen und Oberflaechenalkoxide als Intermediate identifiziert. Die Isomerisierung von Butenen in der H-Ferrierit-Pore wird mit der Umlagerung linearer Butylkationen in der Gasphase verglichen. Der geschwindigkeitsbestimmende Schritt ist in beiden Faellen die Bildung des tert-Butylkations aus einem methylverbrueckten Butylkation. Die CCSD(T)-Methode ist zur Bestimmung genauer Energieprofile erforderlich.
In this work, the long-range dispersion correction for density functional theory is extended to periodic boundary conditions. The influence of the dispersion correction on energy and structural parameters is shown for graphite. The calculated values of the interlayer distance and the interaction energy are in good agreement with experimental ones. By a series of cluster calculations it is shown, that the dispersion correction converges very slowly with respect to the system size. The accurate description of the dispersion interaction between graphite layers requires the usage of PBE+D method applying periodic boundary conditions or embedded cluster models. For structural parameters, the PBE+D methods compares well with the accurate but computationally very demanding [MP2:PBE+CCSD(T)] method. However, the calculated reaction energies differ remarkably. The newly developed, efficient [PBE+D + MP2 + CCSD(T)] method extends the PBE+D energy by two correction terms. The first one, the MP2 correction, rectifies the over stabilization of polar structures (PBE) by a MP2 calculation at the basis set limit. The second term verifies the MP2 correction by a CCSD(T) calculation for a small cluster model. The [PBE+D + MP2 + CCSD(T)] method is applied for the reaction of C4H8 hydro carbons witr the zeolite Ferrierite. Within the pore of a zeolite, pi complexes, butyl cations and surface alkoxides are identified as minima on the potential energy surface. The isomerization of butenes is compared to the rearrangement of linear butyl cations in the gas phase. In both cases, the rate determining step is the formation of the tertial butyl cation from a methyl bridged cation. The CCSD(T) method is for the determination of accurate energy profiles required.

Styles APA, Harvard, Vancouver, ISO, etc.

Miroshnichenko, O. (Olga). « Properties of binary oxides:a DFT study ». Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223018.

Texte intégral

Résumé :

Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is considered
Tiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille
Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., & Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., & Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., & Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046

Styles APA, Harvard, Vancouver, ISO, etc.

Ciro, Guido. « TD-DFT and TD-DFT/PCM approaches to molecular electronic excited states in gas phase and in solution ». Doctoral thesis, Scuola Normale Superiore, 2011. http://hdl.handle.net/11384/85797.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Lövgren, Robin. « Four-component DFT calculations of phosphorescence parameters ». Thesis, Linköping University, Computational Physics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-19180.

Texte intégral

Résumé :

Oscillator strengths and transition energies are calculated for several mono-substitutes of benzene and naphthalene molecules. The substituents investigated are chlorine, bromine and iodine. Calculations for these molecules are presented, at the Hartree-Fock and DFT level of theory. The functional used in DFT is CAM-B3LYP.

Styles APA, Harvard, Vancouver, ISO, etc.

Rowson, Quinton Anthony. « Steady-state vibration of DFT locomotive cabs ». Thesis, University of Canterbury. Mechanical Engineering, 2001. http://hdl.handle.net/10092/6624.

Texte intégral

Résumé :

Back injuries and other illnesses for Tranz Rails Locomotive Engineers, is claimed to be attributed to vibration of locomotive cabs. The purpose of this research was to conduct a study in order to determine the complex motion of a DFT locomotive cab and to objectively and quantifiably measure the vibration present in the locomotive. This thesis examines the ability of a six Degrees Of Freedom rigid body mathematical model of a DFT locomotive cab to determine the natural frequencies present. The goal was to use this model to provide information on different mount alternatives, in order to reduce vibration. The results of this model were inadequate for the selection of another elastomeric mounting alternative. While experimental test of the locomotive cab showed that the rigid body assumption was valid it was found that there are other continuous vibrations and non-linear effects that are also very important in determining cab vibration. Auto-correlation results from acceleration measurements at the base of the mounts were overlaid with the cross-correlation of the acceleration measurements of the cab side of the mounts. These results showed that the current mounts have 100% transmissibility. In some cases and directions the mount was shown to actually amplify the vibrational input from the locomotive. The amplitude of the steady-state vibration of the locomotive cab that was being transmitted was so great that it rendered the dynamic characteristics of the cab insignificant. From the experimental results, the elastomeric mounts were found to be incapable of attenuating the vibration. In addition, the vibration levels due to locomotive running are found to be well above comfort levels of various publications.

Styles APA, Harvard, Vancouver, ISO, etc.

Knottenbelt, Sushilla. « A DFT study of metal-metal bonding ». Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424531.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Reinhold, Meike. « A DFT study of organometallic reaction mechanisms ». Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247161.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Plus de sources

Livres sur le sujet "DFRT"

Shimizu, Takayasu. Theoretical Investigations of the Acetylene Analogues of Group 14 Elements E2X2 (E=Si-Pb, X=F-I). Marburg : Philipps-Universität Marburg, 2011.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. DFT - Diskrete Fourier-Transformation. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Heideman, Michael T. Multiplicative Complexity, Convolution, and the DFT. New York, NY : Springer New York, 1988. http://dx.doi.org/10.1007/978-1-4612-3912-3.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Heideman, Michael T. Multiplicative Complexity, Convolution, and the DFT. New York, NY : Springer New York, 1988.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

S, Burrus C., dir. Multiplicative complexity, convolution, and the DFT. New York : Springer-Verlag, 1988.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Henson, Van Emden. DFTS on irregular grids : The anterpolated DFT. Monterey, Calif : Naval Postgraduate School, 1992.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Budiman, Arief Suriadi. Principles of Extreme Mechanics (XM) in Design for Reliability (DfR). Singapore : Springer Singapore, 2022. http://dx.doi.org/10.1007/978-981-15-6720-9.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Hendriks, Richard C., Timo Gerkmann et Jesper Jensen. DFT-Domain Based Single-Microphone Noise Reduction for Speech Enhancement. Cham : Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-031-02564-8.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Wang, Francis C. Digital circuit testing : A guide to DFT and other techniques. San Diego : Academic Press, 1991.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Briggs, William L. The DFT : An owner's manual for the discrete Fourier transform. Philadelphia : Society for Industrial and Applied Mathematics, 1995.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Plus de sources

Chapitres de livres sur le sujet "DFRT"

Hamza, Rafik, Alzubair Hassan et Akash Suresh Patil. « A Lightweight Secure IoT Surveillance Framework Based on DCT-DFRT Algorithms ». Dans Machine Learning for Cyber Security, 271–78. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-30619-9_19.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Petersen, Christian. « DFR/IDFR — DFT/IDFT — FFT/IFFT (Anhang J) ». Dans Dynamik der Baukonstruktionen, 1167–91. Wiesbaden : Vieweg+Teubner Verlag, 2000. http://dx.doi.org/10.1007/978-3-322-80314-6_32.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Einleitung ». Dans DFT - Diskrete Fourier-Transformation, 1–2. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_1.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Mathematische Strukturen ». Dans DFT - Diskrete Fourier-Transformation, 3–15. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_2.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Definition der DFT ». Dans DFT - Diskrete Fourier-Transformation, 17–46. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_3.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Eigenschaften der DFT ». Dans DFT - Diskrete Fourier-Transformation, 47–96. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_4.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Korrespondenzen der DFT ». Dans DFT - Diskrete Fourier-Transformation, 97–123. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_5.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Schnelle Fourier-Transformation ». Dans DFT - Diskrete Fourier-Transformation, 125–39. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_6.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Neubauer, André. « Schnelle Faltung ». Dans DFT - Diskrete Fourier-Transformation, 141–64. Wiesbaden : Vieweg+Teubner Verlag, 2012. http://dx.doi.org/10.1007/978-3-8348-1997-0_7.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

McFee, Brian. « DFT invertibility ». Dans Digital Signals Theory, 145–54. Boca Raton : Chapman and Hall/CRC, 2023. http://dx.doi.org/10.1201/9781003264859-7.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Actes de conférences sur le sujet "DFRT"

Endrinal, Lesly, Rakesh Kinger, Wilson Pradeep, Shruti Mittal, Jehan Saujauddin, Sean Ho, Jyotika Suri, Atul Chittora, Mark Kassab et Peter Orlando. « Solving Complex Electrical Fault Isolation Challenges with Innovative DFT Strategies ». Dans ISTFA 2024, 125–34. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.istfa2024p0125.

Texte intégral

Résumé :

Abstract As System-on-a-Chip (SoC) continues to increase in complexity, multiple functionalities are being integrated into one integrated circuit (IC). This requires optimization of Design-for-Testability (DFT) strategies to minimize test time while still ensuring full test coverage of the entire chip. It has led to the widespread adoption of Tessent Streaming Scan Network (SSN) architecture on advanced technology nodes. Unlike traditional scan architectures that send data directly to the scan chains, SSN breaks down the data into packets and optimizes the delivery of these packets to allow efficient, concurrent testing of any number of cores. However, SSN presents a challenge for failure analysis, as it becomes extremely difficult to directly modify the SSN patterns on the fly to create a stimulus that will be used for many of the electrical fault isolation (EFI) techniques such as Laser Voltage Imaging (LVI) and Probing (LVP), Dynamic Laser Stimulation (DLS) and Photon Emissions Analysis (PEM). Key challenges include the inability to loop test patterns, run periodic sequences and no visibility of the scan control and clock signals, since these signals are internally generated by the SSH during retargeting. This paper introduces a new Tessent DFT enhancement developed by Siemens called the “LVX mode”. It is the first feature designed to enable Failure Analysis within a DFT tool, utilizing specific DFT hardware for implementation. In addition, another DFT feature which enables writing special pattern annotations that will indicate the start and end of a capture window and the location of all the capture pulses within that window for a particular pattern will also be presented, together with a methodology that will enable static Photon Emissions on SSN patterns. Since on-the-fly modification of the patterns is not possible in SSN, this paper will present two methods that would allow for a more effective and efficient DLS looping. Lastly, the paper will showcase multiple use cases that demonstrate the effectiveness of these identified DFT enhancements for FA.

Styles APA, Harvard, Vancouver, ISO, etc.

Markowitz, Matthew, Kevin Zelaya et Mohammad-Ali Miri. « A Compact Photonic Architecture for General Linear Transformations ». Dans CLEO : Fundamental Science, FW3Q.4. Washington, D.C. : Optica Publishing Group, 2024. http://dx.doi.org/10.1364/cleo_fs.2024.fw3q.4.

Texte intégral

Résumé :

This letter introduces a photonic architecture that enables the realization of arbitrary complex-valued matrices. This is achieved by interlacing amplitude-and-phase diagonal matrices combined with unitary DFrFT matrices. Numerical convergence and resilience to defects are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

Dong, Xin, Yi Zhou, Xiaoxiao Wen et Kenneth Kin-Yip Wong. « Scalable Optical Neural Network Based on Parametric Process ». Dans CLEO : Applications and Technology, AF2D.3. Washington, D.C. : Optica Publishing Group, 2024. http://dx.doi.org/10.1364/cleo_at.2024.af2d.3.

Texte intégral

Résumé :

An optical neural network based on parametric process is demonstrated, and DFT is applied to realize a computation frame rate of up to 40MHz. The MNIST-digit dataset classification accuracy is improved to 87.7%.

Styles APA, Harvard, Vancouver, ISO, etc.

Salunke, Bharti Ahuja, et Sharad Salunke. « Analysis of encrypted images using discrete fractional transforms viz. DFrFT, DFrST and DFrCT ». Dans 2016 International Conference on Communication and Signal Processing (ICCSP). IEEE, 2016. http://dx.doi.org/10.1109/iccsp.2016.7754390.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Qi, Ziyuan, Tianping Huang, Rajendra Kalgaonkar et Fahd AlGhunaimi. « A Novel and Cost-Effective Dry Friction Reducer Based Slickwater for Unconventional Reservoir Stimulation ». Dans SPE/IATMI Asia Pacific Oil & Gas Conference and Exhibition. SPE, 2023. http://dx.doi.org/10.2118/215263-ms.

Texte intégral

Résumé :

Abstract Slickwater has been the most widely used fracturing fluid in stimulation of unconventional reservoirs. Friction reducers (FRs) are one of the key components in a slickwater formulation, while dry FRs (DFRs) are gaining more attention because of logistical and operational benefits. This study aims to develop a cost-effective DFR based slickwater that dissolves quickly with low chemical dosage for slickwater fracturing. Hydration time of the DFRs in synthetic brine was measured by viscosity monitoring. The rheological properties were measured using rheometer. Friction reduction performances of the DFR samples were characterized by an industry standard flow loop apparatus. The breakability experiments were conducted at 82°C by mixing breakers with DFR solution, and broken fluid was tested on rheometer and gel permeation chromatography (GPC). Flow-back performance of slickwater was estimated using proppant packed chromatographic column. Formation damage evaluation was characterized by measuring core permeability before and after slickwater injection at high temperature. DFR powder usually contains two times more effective content than liquid friction reducer with same weight, which significantly reduces logistical costs in operation. To tackle the possible lumping of DFR during hydration, a comprehensive evaluation on polymer hydration time was conducted. Viscosity measurements were used to quantitatively compare the hydration time of different DFR samples. An optimum DFR candidate was able to totally dissolve in synthetic brine in less than 2 minutes. The friction reduction can reach up to 75% in 2 minutes for the DFR solutions, and even at a concentration as low as one pound per thousand gallons (pptg). With the addition of flow-back enhancer and polymer breaker, the formation damage of slickwater to core plug is reduced to less than 12%. In the end, one slickwater formulation was developed, with excellent performance in compatibility, viscosity, flow-back percentage, formation damage restoration and friction reduction, which was recommended for field operation. A novel DFR based slickwater was developed to overcome DFR's hydration and compatibility issues. Analysis on the performance of DFR based chemicals makes this cost-effective slickwater fracturing technology available for field operations.

Styles APA, Harvard, Vancouver, ISO, etc.

Qi, Z. Y., T. P. Huang, R. Kalgaonkar et Q. Sahu. « Towards Freshwater Conservation : Seawater Based Dry Friction Reducer for Slickwater Fracturing ». Dans SPE Conference at Oman Petroleum & Energy Show. SPE, 2024. http://dx.doi.org/10.2118/218518-ms.

Texte intégral

Résumé :

Abstract Hydraulic fracturing with slickwater has been widely used in development of unconventional reservoirs. One of the key components in slickwater formulation is friction reducer (FR). Regular slickwater fracturing operation requires huge amount of low-salinity water, which poses great challenges in areas with freshwater shortage. This study aims to develop slickwater formulation using high performance dry friction reducer (DFR) that can be fast dissolved in seawater to reduce freshwater usage. The DFR products were evaluated in several key aspects, including hydration time, viscosity, friction reduction, and flow-back performance. Hydration time of the DFRs in synthetic brine was measured by viscosity monitoring. The viscosity was measured using rheometer at 160°F. Friction reduction of DFR samples was characterized by industry standard friction flow loop system. Formation damage evaluation was conducted by measuring permeability of core plug before and after slickwater injection at 270°F. The DFRs are cost effective and easy for logistic handling under harsh environmental conditions comparing to liquid and emulsified FRs. To ensure the successful use of DFR with seawater, the evaluation on polymer hydration time was conducted. Viscosity measurements were used to quantitatively compare the hydration time for different DFR samples. An optimum DFR candidate was able to totally dissolve in seawater in 1 minutes, and similar hydration performance in brines with salinity range from 58,000 ppm to 315,000 ppm. The friction reduction can reach 74% in 2 minutes, at low concentration around 2 pounds per thousand gallons (pptg). The relatively high viscosity of slickwater solution ensures the proppant carrying during hydraulic fracturing. A slickwater formulation containing several components was also developed using seawater. Because of the high salinity, the compatibility of different components was investigated, the formulation was able to reach high retained permeability ratio over 85%, The excellent performance of the slickwater makes it promising for field trial. The seawater suitable DFR based slickwater was developed to perform properly under unique environmental conditions. The excellent performance of DFR based chemicals makes this slickwater fracturing technology available for field operations and assist the conservation of freshwater.

Styles APA, Harvard, Vancouver, ISO, etc.

Xu, L. M., Z. Y. Qi, T. P. Huang et R. Kalgaonkar. « Sustainable Approach of Turning Oily Produced Water into Slickwater for Unconventional Reservoir Development ». Dans SPE Water Lifecycle Management Conference and Exhibition. SPE, 2024. http://dx.doi.org/10.2118/219021-ms.

Texte intégral

Résumé :

Abstract Produced water (PW) is generated in a large amount worldwide and has complex compositions. PW treatment is required to meet environmental regulations as well as reuse and recycling of PW. Meanwhile, plenty of water is needed for slickwater fracturing applications during unconventional reservoir development. This study aims to find effective ways to treat PW and formulate it into slickwater for fracturing operations to save fresh water and improve water sustainability. A synthetic high salinity oily produced water with overall salinity of more than 100,000 ppm was used. Searching effective chemicals and optimizing their dosages for PW treatment were based on measurements of oil-water separation time, floc volume and transmission intensity using stability analyzer which allows a step-by-step vertical scanning of dispersions. After treatment, PW was used to prepare slickwater. Hydration time and viscosity of selected dry friction reducer (DFR) in the PW were measured by rheometer, and friction reduction performance of the slickwater was evaluated by a standard friction flow loop system. The developed chemicals are efficient and economical for the PW treatment with short oil-water separation time, high oil removal efficiency, and low chemical dosage. Floc formed quickly and separated from the water phase in several minutes after chemical addition and clear bottom phase was observed. The oil content was reduced to less than 20ppm and total suspended solid was reduced by 80% within 10 minutes with the addition of 30ppm chemical. DFRs for unconventional reservoir development are selected in this work because of simple logistic handling under harsh environmental conditions comparing to liquid and emulsified friction reducers. An optimized DFR formulation which was compatible with treated PW was developed. The DFR was able to totally dissolve in PW in 1 minute. The viscosity of DFR in treated PW at different temperatures was almost same as that of solution prepared using synthetic brine. The friction reduction can reach up to 75% in less than 2 minutes. This indicates that the PW after treatment is applicable for either re-injection or reuse as base water for slickwater fracturing. This work provides the insight of oily produced water treatment by chemical method for slickwater fracturing. This significantly alleviates oilfield produced water discharge and improves water sustainability by saving large volume of fresh water for unconventional reservoir development.

Styles APA, Harvard, Vancouver, ISO, etc.

Haqparast, S., D. Zeinabady et C. R. Clarkson. « Investigating the Effect of Capillary Pressure on DFIT and DFIT-FBA Analysis ». Dans SPE Canadian Energy Technology Conference and Exhibition. SPE, 2024. http://dx.doi.org/10.2118/218067-ms.

Texte intégral

Résumé :

Abstract The diagnostic fracture injection test (DFIT), and the new variation DFIT-FBA (FBA = flowback analysis), are well-testing methods performed before the main hydraulic fracturing operations to obtain several key parameters used in hydraulic fracture design and for reservoir simulation input. The classic (conventional) DFIT includes the sequence of pump-in, followed by a long shut-in (hours to days), while DFIT-FBA utilizes the sequence of pump-in, followed by a brief (minutes) shut-in, and then flowback to accelerate the time to reach closure and obtain reservoir pressure. While DFITs are still widely implemented, DFIT-FBA has the advantage that key properties can be derived in a matter of 2-3 hours versus (typically) more than a day for a conventional DFIT. The current models used to estimate reservoir parameters from DFIT and DFIT-FBA require calculating the fracturing fluid leakoff volume into the reservoir. While mechanisms affecting leakoff include viscous, capillary, and osmotic forces, current DFIT models only consider viscous forces. While the effect of the capillary pressure on fluid leakoff has been explored and confirmed by multiple researchers, it has not been incorporated into models and software for hydraulic fracture modelling or DFIT/DFIT-FBA analysis. An important question addressed in this work is whether the capillary pressure effect is significant over the short timeframe of the DFIT/DFIT-FBA test. Simulation results generated herein demonstrate that capillary pressure plays a significant role in the leakoff of hydraulic fracturing fluid into the reservoir during DFIT/DFIT-FBA tests; therefore, neglecting the effect of capillary pressure in the analyses can lead to substantial errors in reservoir parameter determination. Numerical simulation results also demonstrate that the presence of capillary forces accelerates leakoff and consequently the time of closure. For a simulated DFIT-FBA executed in an unconventional gas reservoir, approximately 25% of the total leakoff volume is attributable to capillary forces. Ignoring the effect of capillary pressure results in ~77% overestimation of reservoir permeability. Similarly, for a simulated DFIT case, this contribution is up to 26.5%, leading to ~77% overestimation of reservoir permeability. A sensitivity analysis performed herein underscores the significance of considering interfacial tension and contact angle, while reservoir permeability has a relative influence on the outcomes. Consequently, the early-time leakoff permeability estimated from DFIT/DFIT-FBA tests with current models is more precise for situations where there is reduced interfacial tension between the rock and fracturing fluid, and/or when the rock demonstrates mixed wettability.

Styles APA, Harvard, Vancouver, ISO, etc.

Clarkson, C. R., D. Zeinabady, B. Zanganeh et S. Haqparast. « Learnings from Over 5 Years of Design, Implementation, and Analysis of the Modified Flowback DFIT, DFIT-FBA ». Dans SPE Hydraulic Fracturing Technology Conference and Exhibition. SPE, 2025. https://doi.org/10.2118/223557-ms.

Texte intégral

Résumé :

Abstract The diagnostic fracture injection test (DFIT’) has become a standard well-test method applied to obtain critical information (e.g., minimum in-situ stress, reservoir pressure and permeability, etc.) for the evaluation of low-permeability (‘unconventional’) reservoirs. In modern applications, DFITs are commonly performed at the toe of horizontal wells. The conventional (pump-in/shut-in) DFIT involves pumping into the well at high pressure to create and propagate a small hydraulic fracture, and then shutting in the well with the resulting pressure falloff evaluated using pressure-transient analysis (PTA) approaches to obtain the various parameters of interest. However, extensive test times (days, weeks, or even months) may be required to acquire information such as reservoir pressure. As an alternative, a modified version of a flowback DFIT, referred to as ‘DFIT-FBA’ (where FBA = flowback analysis), was recently introduced to accelerate information obtained from a DFIT. After the pump-in stage, a brief shut-in (~ 5 minutes) is followed by flowback of the well at a (rule-of-thumb) initial flowback rate of 2-5% of the injection rate for (typically) 2-4 hours. Recent studies have suggested that, with properly designed, implemented, and analyzed DFIT-FBA tests, all of the same information can be obtained as a conventional DFIT, but in a fraction of the time. This time savings has created new opportunities for DFIT applications (e.g., multiple along-well tests performed in a day) that were not previously practical with a conventional DFIT. However, DFIT-FBA is a relatively new method (introduced in 2019), with over 300 tests being performed to date, and continuous improvements are being made. The objective of this paper is to share the learnings from over 5 years of design, implementation, and analysis of DFIT-FBA in the field, with an emphasis on analysis. To achieve this, the theoretical background for DFIT-FBA interpretation developed by the authors, which is rooted in rate-transient analysis (RTA), is reviewed, and the practical application of a DFIT-FBA analysis workflow is demonstrated using simulated and field cases. For completeness and comparison purposes, the conventional DFIT (PTA-based) workflow is demonstrated using conventional DFIT simulated and field cases. The conventional DFIT workflow is also applied to field cases of the precursor to DFIT-FBA, the ultra-low flowback rate (<0.1% of injection rate) DFIT, where the influence of flowback rate on the analysis is ignored. The primary findings from the analysis of DFIT-FBA are as follows: Flowback rates must be measured to 1) correct for near-wellbore tortuosity (particularly important for horizontal wells) and perforation friction – failure to do so will result in an under-estimate of minimum in-situ stress; 2) identify flow regimes (using a log-log plot of rate-normalized pressure, and its derivative with respect to the natural log of material balance time, versus material balance time), and estimate pore pressure using the flow-regime identification plot; and 3) perform before-closure straight-line (rate-transient) analysis to obtain permeabilityApplication of conventional DFIT (PTA-based) analysis approaches, which ignore the effect of flowback rates, consequently result in significant errors in critical parameter determination; for example, application of this approach to the simulated DFIT-FBA example results in a permeability estimate that is approximately two orders of magnitude different from the simulator input valuePore pressure estimation from the flowback portion of DFIT-FBA test is currently the most uncertain aspect of test interpretation; it is recommended that select DFIT-FBA tests are followed by shut-in (rebound) tests to obtain an independent estimate of reservoir pressure It is hoped that the findings of this study can be used by operators to increase the chance of obtaining successful test results. While DFIT-FBA is showing much promise as a new well-testing method, there are improvements that can be made in test design, implementation, and analysis.

Styles APA, Harvard, Vancouver, ISO, etc.

Medlar, Michael P., et Edward C. Hensel. « Validation of an Enhanced Dispersion Algorithm for Use With the Statistical Phonon Transport Model ». Dans ASME 2020 Heat Transfer Summer Conference collocated with the ASME 2020 Fluids Engineering Division Summer Meeting and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ht2020-8926.

Texte intégral

Résumé :

Abstract Computer simulations of quasi-particle based phonon transport in semiconductor materials rely upon numerical dispersion relations to identify and quantify the discrete energy and momentum states allowable subject to quantum constraints. The accuracy of such computer simulations is ultimately dependent upon the fidelity of the underlying dispersion relations. Dispersion relations have previously been computed using empirical fits of experimental data in high symmetry directions, lattice dynamics, and Density Function Theory (DFT) or Density Functional Perturbation Theory (DFPT) approaches. The current work presents high fidelity dispersion relations describing full anisotropy for all six phonon polarizations with an adjustable computational grid. The current approach builds upon the previously published Statistical Phonon Transport Model (SPTM), which employed a first nearest neighbor lattice dynamics approach for the dispersion calculation. This paper extends the lattice dynamics approach with the use of both first and second nearest neighbors interactions that are quantified using published interatomic force constants calculated from DFT. The First Brillouin Zone (FBZ) is segmented into eight octants of high symmetry, and discretized in wave vector space with a 14 by 14 by 14 grid. This results in 65,586 states of unique wave vector and frequency combinations. Dispersion calculations are performed at each of the six faces of the wave vector space volume elements in addition to the centroid, resulting in 460,992 solutions of the characteristic equations. For the given grid, on the order of 108 computations are required to compute the dispersion relations. The dispersion relations thus obtained are compared to experimental reports available for high symmetry axes. Full anisotropic results are presented for all six phonon polarizations across the range of allowable wave vector magnitude and frequency as a comprehensive model of allowable momentum and energy states. Results indicate excellent agreement to experiment in high symmetry directions for all six polarizations and illustrate an improvement as compared to the previous SPTM implementation. Dispersion relations based on the lattice dynamic model with first and second nearest neighbor atomic interactions relying upon DFT calculated inter-atomic force constants provides an accurate high fidelity energy and momentum model for use in phonon transport simulations.

Styles APA, Harvard, Vancouver, ISO, etc.

Rapports d'organisations sur le sujet "DFRT"

Wills, Ann. DFT (and DMFT) for DFT users. Office of Scientific and Technical Information (OSTI), juillet 2023. http://dx.doi.org/10.2172/1989140.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Dodge, D. DFTT report for Signal Analysis 2023. Office of Scientific and Technical Information (OSTI), juillet 2023. http://dx.doi.org/10.2172/1992195.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Henson, Van Emden. DFTS on Irregular Grids : The Anterpolated DFT. Fort Belvoir, VA : Defense Technical Information Center, mars 1992. http://dx.doi.org/10.21236/ada255187.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Samolyuk, German D., Stanislav I. Golubov, Yury N. Osetskiy et Roger E. Stoller. DFT STUDY REVISES INTERSTITIAL CONFIGURATIONS IN HCP Zr. Office of Scientific and Technical Information (OSTI), juin 2012. http://dx.doi.org/10.2172/1048714.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Nelson, Tammie. DFT for design and characterization of functional materials. Office of Scientific and Technical Information (OSTI), mars 2021. http://dx.doi.org/10.2172/1772398.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Shaw, Kaden, Maia Ketteridge et Lan Li. Comparison of DFT Basis Sets for Organic Dyes. Peeref, juillet 2022. http://dx.doi.org/10.54985/peeref.2207p2702048.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Synowczynski, Jennifer, Jan W. Andzelm et D. G. Vlachos. DFT Study of H2 Combustion on alphaAl2O3 Supported Pt Clusters. Fort Belvoir, VA : Defense Technical Information Center, novembre 2008. http://dx.doi.org/10.21236/ada491362.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Huang, Aris, Debbie Wong, Elizabeth Cassity et Jennie Chainey. Teacher development multi-year studies : Impact of COVID-19 on teaching practices in Lao PDR, Timor-Leste and Vanuatu : A discussion paper for practitioners and policymakers. Australian Council for Educational Research, 2022. http://dx.doi.org/10.37517/978-1-74286-680-2.

Texte intégral

Résumé :

The COVID-19 pandemic caused significant disruptions to education systems around the world. Many governments responded abruptly, quickly closing schools and transitioning to home learning. This paper explores the impact of extended school closures due to COVID-19 on teaching and student learning in three countries – Lao People’s Democratic Republic (Laos), Timor-Leste and Vanuatu. This research extends the Australian Government’s Department of Foreign Affairs and Trade (DFAT)’s multi-year Teacher Development Studies, which are commissioned under the Evaluation Analytics Service (EAS). This study series involves the investigation of DFAT-funded teacher development initiatives in Laos, Timor-Leste and Vanuatu to understand the extent to which the investments have improved teaching quality and student learning. In 2021, regular data collection for the study was extended to include COVID-19 impact questions, thereby providing an opportunity to understand a wide range of education stakeholder perspectives on their experience of transitioning and implementing home learning, the impact on teaching practices and student learning, and the level of support teachers were provided during the pandemic.

Styles APA, Harvard, Vancouver, ISO, etc.

Lu, Shuai, et Michael CW Kintner-Meyer. Scoping Study for Demand Respose DFT II Project in Morgantown, WV. Office of Scientific and Technical Information (OSTI), juin 2008. http://dx.doi.org/10.2172/936762.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Pai, Sharmila V., Cary F. Chabalowski et Betsy M. Rice. Ab Initio and DFT Potential Energy Surfaces for Cyanuric Chloride Reactions. Fort Belvoir, VA : Defense Technical Information Center, juillet 1998. http://dx.doi.org/10.21236/ada351780.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Nous offrons des réductions sur tous les plans premium pour les auteurs dont les œuvres sont incluses dans des sélections littéraires thématiques. Contactez-nous pour obtenir un code promo unique!