1,723,649 research outputs found
INVESTIGATION OF SEISMIC SLIP IN EXPERIMENTAL FAULTS UNDER HYDROTHERMAL CONDITIONS
Full text linkLa rigidità della roccia e l'evoluzione dell'attrito con la velocità e la distanza di scivolamento controllano la meccanica dei terremoti e il ciclo sismico. Questa interpretazione fisica si basa anche su esperimenti di attrito nelle rocce effettuati a basse (~1 mm/s, sub-sismiche) e alte (~1 m/s, cosismiche) velocità di scivolamento. Tuttavia, lo studio dell'attrito delle rocce in condizioni idrotermali e a velocità di scivolamento (0,01-1 m/s) e per rigetti (> 0,1 m) tipici dei terremoti è stata in parte ostacolata da problemi tecnici. In questa tesi, mi propongo di comprendere meglio il comportamento dell’attrito di faglie sperimentali in presenza di fluidi caldi e pressurizzati durante il ciclo sismico, mediante esperimenti condotti con macchine tipo rotary e indagini microanalitiche.
Nella prima parte della tesi, ho studiato l'effetto dello stato fisico dell'acqua sul coefficiente di attrito. I risultati sperimentali mostrano che la presenza di acqua pressurizzata allo stato liquido e supercritico, rispetto a quella allo stato di vapore (e in condizioni asciutte), abbassa il coefficiente d’attrito di una faglia di gabbro del 50-60% a velocità di scorrimento sub-sismiche (e.g., 10 mm/s).
Ho quindi effettuato esperimenti in condizioni idrotermali per studiare l’attrito delle faglie nella fase intersismica del ciclo sismico. I risultati mostrano che la relazione log-lineare tra l’incremento di attrito e tempo di contatto si riduce ad alte temperature e, soprattutto, in presenza di fluidi. Questo comportamento è attribuito agli effetti contrastanti dell'aumento dell'area di contatto rispetto alla diminuzione della forza di contatto delle asperità durante il tempo di contatto (o intersismico).
Ho infine studiato la dipendenza della stabilità dell'attrito con il rigetto effettuando esperimenti su polveri di roccia deformate a temperature e pressionei prossime a quelle della transizione fragile-duttile. I risultati sperimentali mostrano che la transizione da comportamento velocity-weakening e potenzialmente instabile a velocity-strengthening e stabile avviene all’aumentare del rigetto ed è associata alla transizione da una deformazione localizzata a distribuita nello strato di polvere.
I risultati presentati in questa tesi sfidano in alcuni casi le nostre attuali conoscenze sull'attrito delle rocce in condizioni idrotermali e forniscono nuove possibili interpretazioni sul comportamento meccanico delle faglie durante il ciclo sismico.Rock stiffness and the evolution of rock friction with slip velocity and slip displacement control earthquake mechanics and the seismic cycle. This physical interpretation is also based on rock friction experiments where low (~1 m/s, sub-seismic) to high (~1 m/s, seismic) slip velocities were imposed on simulated faults. However, the investigation of rock friction under hydrothermal conditions at slip velocities (0.01-1 m/s) and displacements (> 0.1 m) typical of earthquakes has been partly hampered by technical challenges. In this thesis, I aim at better understanding the frictional behavior of experimental faults in the presence of hot and pressurized fluids during the seismic cycle by means of rotary shear experiments and micro-analytical investigations.
First, I investigated the effect of the physical state of water on frictional strength. Experimental results show that the presence of pressurized water in liquid and supercritical states, compared to in vapor state (and dry conditions), weakens the fault strength of gabbro of 50-60% at sub-seismic slip velocities (e.g., 10 m/s).
Then, I performed slide-hold-slide experiments under hydrothermal conditions to investigate frictional healing during the seismic cycle. The results show that the log-linear relation between frictional healing and hold time is relaxed at high temperatures and, especially, in the presence of fluids. This behavior is attributed to the contrasting effects of contact area increase vs. contact strength decrease of the asperities during the holds.
Finally, I studied the slip dependence of frictional stability in large displacement experiments performed on gouges at conditions close to brittle-ductile transition. The results show that the transition from velocity-weakening (potentially unstable) to velocity-strengthening (stable) behavior is promoted by slip displacement and is associated with the transition from localized to distributed deformation in the gouge layer.
The results presented in this thesis challenge in some cases our current knowledge of rock friction under hydrothermal conditions and may provide new insights into the mechanical behavior of faults during the seismic cycle
Structure-activity studies of novel noncamptothecin topoisomerase I-targeting agents
No full textTopoisomerases are ubiquitous enzymes that participate in processes such as DNA replication, transcription and repair. Two camptothecin derivatives, topotecan (Hycamtin®) and irinotican (CPT-11/ Camptosar®), are currently used in the clinic as topoisomerse I targeting anticancer agents. Camptothecins can stabilize the enzyme-DNA cleavage complex, leading to DNA damage and ultimately cell death. Despite their unique tumor suppression mechanism, topotecan and irinotican can undergo hydrolysis and inactivation in vivo due to an unstable lactone moiety. In addition, both topotecan and irinotican are substrates for efflux transporters, BCRP and MDR1, which are associated with drug resistance. 8,9-Dimethoxy-5-(2-dimethylaminoethyl)-2,3-methylenedioxy- 5H-dibenzo[c,h][1,6]naphthyridine-6- one (ARC-111) has been identified as exceptionally active TOP1-targeting agent with potent antitumor activity both in vitro and in vivo. Unlike camptothecins, ARC-111 is not a substrate for major efflux transporters, and does not bind to human serum albumin. ARC-111 structurally related analogs, 12-carboxamides of benzo[i]phenathridine and the "reversed lactams" have also exhibited excellent cytotoxicity and potent TOP1 targeting activity. In this dissertation, further insights into structure-activity relationship of ARC-111 and related compounds have been carefully examined. Alteration of both D-ring and side chain of ARC-111 have afforded potent TOP1-targeting agents. Inspired by the success of ARC-111, the design, synthesis and biological activities of other B-ring modified benzo[i]phenathridines have been systematically investigated. In review of possible metabolites of ARC-111, together with the known structure-activity relationships associated with the "reversed lactams", 11-carboxamides and 12-carboxamides of benzo[i]phenathridine, have prompted the examination of α,α-dimethyl substitution on the amino side chain on pharmacologic activity. Efficient synthetic methods associated with these novel non-camptothecin anticancer agents have also been developed. Several agents identified in this study have demonstrated excellent cancer cell cytotoxicity, TOP1 targeting specificity, as well as in vivo antitumor efficacy, comparable as the lead compound, ARC-111.Ph.D.Includes bibliographical references (p. 198-218)by Wei Fen
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
sj-pdf-1-hum-10.1177_00187267231165885 – Supplemental material for The double-edged sword of negative supervisor gossip: When and why negative supervisor gossip promotes versus inhibits feedback seeking behavior among gossip targets
No full textSupplemental material, sj-pdf-1-hum-10.1177_00187267231165885 for The double-edged sword of negative supervisor gossip: When and why negative supervisor gossip promotes versus inhibits feedback seeking behavior among gossip targets by Qianlin Zhu, Elena Martinescu, Bianca Beersma and Feng Wei in Human Relations</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Two new species of Kalyptorhynchia (Koinocystididae and Gnathorhynchidae) from China
No full textLin, Yi-Tao, Feng, Wei-Tao, Zhuang, Jie-Yi, Zhang, Yu, Wang, An-Tai (2017): Two new species of Kalyptorhynchia (Koinocystididae and Gnathorhynchidae) from China. Zootaxa 4337 (4): 573-583, DOI: https://doi.org/10.11646/zootaxa.4337.4.
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Two new brackish-water species of Pogaina (Rhabdocoela: Provorticidae) from China
No full textZhong, Lin-Hong, Xie, Yao-Hang, Hu, Xiao-Zhou, Chen, Yu-Si, Feng, Wei-Tao, Zhang, Yu, Wang, An-Tai (2019): Two new brackish-water species of Pogaina (Rhabdocoela: Provorticidae) from China. Zootaxa 4679 (2): 353-364, DOI: 10.11646/zootaxa.4679.2.
Photoinduced anisotropic response of azobenzene chromophore functionalized multiwalled carbon nanotubes
Full text linkThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Yiyu Feng, Wei Feng, Hideki Noda, Akihiko Fujii, Masanori Ozaki, Katsumi Yoshino, Journal of Applied Physics 102, 053102 (2007) and may be found at https://doi.org/10.1063/1.2776220Azobenzene chromophore covalently functionalized multiwalled carbon nanotubes(AZO-MWCNT) were synthesized and their optical properties were investigated by ultraviolet-visible absorption and photoluminescence spectroscopy. The polarized absorption of the AZO-MWCNT film was measured by cross-polarized light along the directions parallel and perpendicular to the incident light under the irradiation of polarized ultraviolet light. Photoinduced optical anisotropy of the AZO-MWCNT film was dominated by the enhanced dipole transition of the nanotube axis parallel to the incident light and the decreased transition perpendicular to light. The unique anisotropy induced by the photo-orientation of azobenzene chromophore provides insight into the polarized optical properties of carbon nanotubes
- …
