233 research outputs found
On Optical Dipole Moment and Radiative Recombination Lifetime of Excitons in WSe2
No full textOptical dipole moment is the key parameter of optical transitions, as it directly determines the strength of light-matter interaction such as intrinsic radiative lifetime. However, experimental determination of these fundamental properties of excitons in monolayer WSe2 is largely limited, because the commonly used measurement, such as (time-resolved) photoluminescence, is inherently difficult to probe the intrinsic properties. For example, dark states below bright exciton can change the photoluminescence emission rate by orders of magnitude and gives an "effective" radiative lifetime distinctive from the intrinsic one. On the other hand, such "effective" radiative lifetime becomes important itself because it describes how dark states affect exciton dynamics. Unfortunately, the "effective" radiative lifetime in monolayer WSe2 is also not determined as it requires photoluminescence measurement with resonant excitation, which is technically difficult. These difficulties are overcome here to obtain both the "intrinsic" and "effective" radiative lifetime experimentally. A framework is developed to determine the dipole moment and "intrinsic" radiative lifetime of delocalized excitons in monolayer WSe2 from the absorption measurements. In addition, the "effective" radiative lifetime in WSe2 is obtained through time-resolved photoluminescence and absolute quantum-yield measurement at resonant excitation. These results provide helpful information for fundamental understanding of exciton light-matter interaction in WSe2
DEVELOPMENT OF SELF-ASSEMBLED CONDUCTING POLYMER ULTRATHIN FILMS AND POLY(ANILINE) NANOWIRES/SOL-GEL COMPOSITE MATERIALS AS SUBSTRATES FOR PLANAR SUPPORTED BIOMIMETIC ARTIFICIAL PHOTOSYNTHETIC SYSTEMS by
No full textRights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author
Interlayer electron-phonon coupling in WSe2/hBN heterostructures
No full textEngineering layer-layer interactions provides a powerful way to realize novel and designable quantum phenomena in van der Waals heterostructures(1-6). Interlayer electron-electron interactions, for example, have enabled fascinating physics that is difficult to achieve in a single material, such as the Hofstadter's butterfly in graphene/boron nitride (hBN) heterostructures(5-10). In addition to electron-electron interactions, interlayer electron-phonon interactions allow for further control of the physical properties of van der Waals heterostructures. Here we report an interlayer electron-phonon interaction in WSe2/hBN heterostructures, where optically silent hBN phonons emerge in Raman spectra with strong intensities through resonant coupling to WSe2 electronic transitions. Excitation spectroscopy reveals the double-resonance nature of such enhancement, and identifies the two resonant states to be the A exciton transition of monolayer WSe2 and a new hybrid state present only in WSe2/hBN heterostructures. The observation of an interlayer electron-phonon interaction could open up new ways to engineer electrons and phonons for device applications
El proyecto arquitectónico en el paisaje del patrimonio moderno de Valladolid. El colegio internado de la Sagrada Familia.
No full textEl Colegio Internado Sagrada Familia está situado a apenas tres kilómetros al sur de la ciudad de Valladolid,
en un área en que la casualidad hizo que en relativamente poca distancia se situasen tres
edificios de uso escolar pioneros de la modernidad en Valladolid. Acompañando al que aquí le comentamos,
se encuentran el Colegio Apostólico de los Padres Dominicos (Fisac, 1957) y el Colegio
de San Agustín (Cecilio Sánchez Robles Tarín, 1961).
La implantación del Colegio Internado Sagrada Familia se produce en un lugar llano ocupado por
los últimos pinos del pinar de Antequera, incorporando al diseño de sus espacios libres la Acequia
de Valladolid. Los árboles de ribera junto al canal y los grandes pinos en toda la parcela, con sus
tallos largos y esbeltos, se convierten en un potente elemento proyectual del que los arquitectos se
sirven con gran inteligencia para crear visiones equilibradas en el edificio. El edificio escolar pretende
mimetizarse con el entorno, pasar desapercibido e integrarse a través de una cuidada elección
de sus materiales. De hecho, en el colegio cuentan como anécdota que los arquitectos vinieron de
Madrid con una maqueta y viendo el solar la giraron y colocaron de tal forma que respetase el
mayor número posible de árboles existentes.Máster en Investigación e Innovación en Arquitectura. Intervención en el Patrimonio, Rehabilitación y Regeneració
A drone detector with modified backbone and multiple pyramid featuremaps enhancement structure (MDDPE)
No full textThis work presents a drone detector with modified backbone and multiple
pyramid feature maps enhancement structure (MDDPE). Novel feature maps improve
modules that uses different levels of information to produce more robust and
discriminatory features is proposed. These module includes the feature maps
supplement function and the feature maps recombination enhancement function.To
effectively handle the drone characteristics, auxiliary supervisions that are
implemented in the early stages by employing tailored anchors designed are
utilized. To further improve the modeling of real drone detection scenarios and
initialization of the regressor, an updated anchor matching technique is
introduced to match anchors and ground truth drone as closely as feasible. To
show the proposed MDDPE's superiority over the most advanced detectors,
extensive experiments are carried out using well-known drone detection
benchmarks.Comment: 20 pages, 10 figure
The effect of wording on message propagation: Topic-and author-controlled natural experiments on twitter.
No full textAbstract Consider a person trying to spread an important message on a social network. He/she can spend hours trying to craft the message. Does it actually matter? While there has been extensive prior work looking into predicting popularity of socialmedia content, the effect of wording per se has rarely been studied since it is often confounded with the popularity of the author and the topic. To control for these confounding factors, we take advantage of the surprising fact that there are many pairs of tweets containing the same url and written by the same user but employing different wording. Given such pairs, we ask: which version attracts more retweets? This turns out to be a more difficult task than predicting popular topics. Still, humans can answer this question better than chance (but far from perfectly), and the computational methods we develop can do better than both an average human and a strong competing method trained on noncontrolled data
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Proteomic allocation by E.coli during growth transitions, from strategy to mechanism
No full textIn different environments, bacteria are known to allocate their proteome differently and achieve different growth rates. Extensive quantitative studies on proteomic allocations in steady states have been done. Yet it’s still not clear how bacteria manage to adjust their proteome responding to different environments through thousands of reactions and eventually reach different growth rates. In order to gain better understanding on the adaptation strategy and mechanism, in my dissertation, I studied the kinetic behavior of E.coli during various environmental changes. Mathematical modeling were used to quantitatively capture the proteomic re-allocation and growth rate adaptation during transitions. Further studies on the kinetics of Guanosine tetraphosphate (ppGpp) and translational elongation rate during growth transition revealed the molecular basis of well-known ribosomal ‘growth law’. In Chapter 2 and 3, we studied the growth transitions from ‘rich media’, a condition with ample amino acids or/and other nutrient supplies. We started with the case of methionine depletion in Chapter 2. MetE were found to be the major bottleneck in met downshift. By adapting the flux-controlled regulatory model established for carbon shift, we quantitatively captured the relationship between pre-shift MetE reserves and lag time before growth recovery. In Chapter 3, we studied the proteomic allocation during all AAs depletion. Quantitative proteomic analysis revealed a linear relationship between the onset time of enzymes across AAs biosynthesis pathways and their fractional reserve in pre-shift condition, indicating a ‘as-needed’ gene expression strategy during all AAs downshift. Combining flux-controlled global regulation and pathway specific end-production inhibition, we successfully captured the proteome recovery kinetics using only data collected in the pre- and post-shift steady-states.
Chapter 4 is focused on bacterial kinetic response to sub-lethal chloramphenicol (an antibiotic inhibiting translation) treatment. By using translational elongation rate as a flux sensor and the key signaling variable, we accurately predicted the kinetics of biomass accumulation and gene expressions.
In Chapter 5, we show that translational elongation rate is inversely proportional to ppGpp, an essential molecule regulating translational machinery, during transient and steady-states. We established ppGpp rate-sensing strategy and thus closed a key regulatory circuit linking ppGpp, growth rate, ribosomal content and translational rate together
The effect of wording on message propagation: Topic-and author-controlled natural experiments on twitter.
No full textAbstract Consider a person trying to spread an important message on a social network. He/she can spend hours trying to craft the message. Does it actually matter? While there has been extensive prior work looking into predicting popularity of socialmedia content, the effect of wording per se has rarely been studied since it is often confounded with the popularity of the author and the topic. To control for these confounding factors, we take advantage of the surprising fact that there are many pairs of tweets containing the same url and written by the same user but employing different wording. Given such pairs, we ask: which version attracts more retweets? This turns out to be a more difficult task than predicting popular topics. Still, humans can answer this question better than chance (but far from perfectly), and the computational methods we develop can do better than both an average human and a strong competing method trained on noncontrolled data
Conjunctively Evolving: Masters of Contemporary Art in China and Britain
No full text'Conjunctively Evolving', was an international exhibition in Shanghai, China, curated by Jian Zhou, Liu Li, and Zhang Yicheng. The exhibition was developed as an extension and progression from the exhibition, "Intersecting Practices: Contemporary Printmaking in the UK", including works by artists based in China and the UK.
Exhibiting artists: Victoria Ahrens, Hadas Auerbach, Trevor Banthorpe, Ian Brown, Jane Bustin, Stephen Chambers RA, Paul Coldwell, Nicky Coutts, Deng Yuejun, Julia Farrer, Hans Fonk, Oona Grimes, Gu Tingting, Gu Renming, Brian D Hodgson, Ji Wenyu, Jiao Yang, Jin Sheng, Ann-Marie Lequesne, Liu Yincong, Mao Weixin, Charlie Masson, Bob Matthews, Heather Meyerratken, Ni Weihua, Peng Bo, Meg Rahaim, Shen Fan, Hal Stennett, Emma Stibbon RA, Jo Stockham, Finlay Taylor, Wang Ming, Wei Guangqing, Joby Williamson, Wu Xiaoning, Xiao Jianhun, Xie Rong, Xuan Chenhao, Zhou Binlang, Zhou Jian, Zhu Weibin
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