10 research outputs found
Oscillations de Bloch et échelle de Wannier Stark dans des superréseaux semiconducteurs
No full textTerahertz (THz) electromagnetic field, which lies in the frequency gap between the infrared and microwave, roughly between 1 THz to 10 THz, is highly desirable for both fundamental research and application. Yet tuneable compact THz sources are still not available. On the other hand, ever since first proposed in 1970, semiconductor superlattice provides new playground for various new technique and devices of tremendous research and application interest. In this thesis, an innovative theme, relying on Bloch oscillations in a dc biased semiconductor superlattice, is explored to realize tunable compact THz source THz Bloch oscillator. For doped superlattice Bloch oscillator, we designed quantum cascade super-superlattice structure to realize Bloch oscillations whilst prohibit electrical domain formation. The designed structures were processed into various waveguide and grating devices for electroluminescence detection using Fourier transform infrared spectroscopy (FTIR). The Bloch gain of semi-insulating surface plasmon waveguide device was also measured using THz time domain spectroscopy. Even though the electroluminescence and gain at THz regime were observed, no direct evidence of Bloch emission was confirmed. For undoped superlattice, the THz emission from Bloch oscillations was observed by time domain spectroscopy. At last, the photocurrent corresponding to heavy hole and Wannier Stark Ladder (WSL) states transitions in undoped superlattice was studied. Under CW laser pumping, the photocurrent as function of the applied voltage showed multiple WSL peaks, which indicated laser induced and controllable negative differential conductance (NDC). With increasing pumping power, the nonlinear NDC regime and bistable states were investigated as well.Le champ électromagnétique térahertz (THz) se situe dans l'intervalle de fréquence entre l'infrarouge et les micro-ondes, à peu près entre 1 THz à 10 THz. Ce domaine est hautement souhaitable tant pour la recherche fondamentale que pour les applications. Pourtant des sources THz compacts et accordables ne sont pas encore disponibles. Depuis la première proposition en 1970, les superréseaux semiconducteurs, dans lequel deux couches semi-conductrices atomiques avec bande interdite différente sont disposés périodiquement, fournissent de nouvelles possibilités. De nouvelles techniques et de nouveaux dispositifs deviennent réalisables. Dans cette thèse, les oscillations de Bloch dans des mini-bandes électroniques d’un superréseau polarise et la dispersion du gain associée sont utilisées pour réaliser une source THz compacte et accordable : l’oscillateur de Bloch THz. Un premier ensemble de dispositifs utilisent des réseaux dopes spécifiquement conçus pour éviter la formation de domaine d’accumulation de charges. Ces dispositifs utilisent une surface semi-isolante ou deux surfaces métalliques permettant un guidage par plasmon de surface. Cependant, malgré la réalisation de couplage par les bords ou par un réseau diffractant en surface et des mesures directes ou avec un interféromètre a transformation de Fourrier (FTIR), l’électroluminescence a été observée dans le domaine térahertz, avec un gain qui n’a pas pu etre relie aux oscillations de Bloch. Avec des superréseaux non dope, l'émission THz des oscillations de Bloch a été détectée par spectroscopie dans le domaine temporel. La dépendance de la fréquence d’émission avec le champ électrique appliqué constitue une preuve directe des oscillations de Bloch. L’échelle de Wannier Stark des trous sous pompage optique continu a aussi été observe dans les superréseaux non dopes. Avec l’augmentation de la puissance de pompage optique, les pics du photocourant se décalent et leurs formes deviennent asymétriques. L’évolution est attribue a l’accumulation des porteurs photogénérés dans les deux couches encadrant le superréseau. En outre, pour une puissance de pompage élevée, la bistabilité du photocourant a été également observée
Choosing Healthy Food in Sydney's Inner City Neighborhoods
No full textAbstractDiet-related chronic diseases are a major health problem faced by developed and developing countries. Although individuals’ dietary patterns are often associated with varied psychological and socioeconomic factors, built environment factors can be important determinants of food choices. Whilst there is some evidence to suggest a link between access to food and food consumption, it remains unclear how a wider range of built environment factors influence residents’ food choices. A deeper understanding of these relationships could reveal under-researched aspects of a healthy built environment. This paper explores how residents in inner Sydney neighborhoods access food and investigates how characteristics of the built environment influence their food choices. Eighteen participants, representing a range of ethnic backgrounds and levels of income, were selected for in-depth interviews. Several urban barriers to healthy food consumption were identified through analysis. Distance, land use and urban form, in particular, shape the food choices of individuals in different ways. These findings have implications for urban planning and policy making for healthy cities
Efficient feature aggregation and scale-aware regression for monocular 3-D object detection
No full textMonocular 3D object detection has received considerable attention for its simplicity and low cost. Existing
methods typically follow conventional 2D detection paradigms,
first locating object centers and then predicting 3D attributes
via neighboring features. However, these approaches mainly
focus on local information, which may limit the model’s global
context awareness and result in missed detections, as the global
context provides semantic and spatial dependencies essential for
detecting small objects in cluttered or occluded environments.
In addition, due to large variation in object scales across
different scenes and depths, inaccurate receptive fields often
lead to background noise and degraded feature representation.
To address these issues, we introduce MonoASRH, a novel
monocular 3D detection framework composed of Efficient Hybrid
Feature Aggregation Module (EH-FAM) and Adaptive ScaleAware 3D Regression Head (ASRH). Specifically, EH-FAM
employs multi-head attention with a global receptive field to
extract semantic features and leverages lightweight convolutional
modules to efficiently aggregate visual features across different
scales, enhancing small-scale object detection. The ASRH encodes
2D bounding box dimensions and then fuses scale features with
the semantic features aggregated by EH-FAM through a scalesemantic feature fusion module. The scale-semantic feature fusion
module guides ASRH in learning dynamic receptive field offsets,
incorporating scale information into 3D position prediction for
better scale-awareness. Extensive experiments on the KITTI and
Waymo datasets demonstrate that MonoASRH achieves state of-the-art performance
Oscillations de Bloch et échelle de Wannier Stark dans des superréseaux semiconducteurs
No full textLe champ électromagnétique térahertz (THz) se situe dans l'intervalle de fréquence entre l'infrarouge et les micro-ondes, à peu près entre 1 THz à 10 THz. Ce domaine est hautement souhaitable tant pour la recherche fondamentale que pour les applications. Pourtant des sources THz compacts et accordables ne sont pas encore disponibles. Depuis la première proposition en 1970, les superréseaux semiconducteurs, dans lequel deux couches semi-conductrices atomiques avec bande interdite différente sont disposés périodiquement, fournissent de nouvelles possibilités. De nouvelles techniques et de nouveaux dispositifs deviennent réalisables. Dans cette thèse, les oscillations de Bloch dans des mini-bandes électroniques d un superréseau polarise et la dispersion du gain associée sont utilisées pour réaliser une source THz compacte et accordable : l oscillateur de Bloch THz. Un premier ensemble de dispositifs utilisent des réseaux dopes spécifiquement conçus pour éviter la formation de domaine d accumulation de charges. Ces dispositifs utilisent une surface semi-isolante ou deux surfaces métalliques permettant un guidage par plasmon de surface. Cependant, malgré la réalisation de couplage par les bords ou par un réseau diffractant en surface et des mesures directes ou avec un interféromètre a transformation de Fourrier (FTIR), l électroluminescence a été observée dans le domaine térahertz, avec un gain qui n a pas pu etre relie aux oscillations de Bloch. Avec des superréseaux non dope, l'émission THz des oscillations de Bloch a été détectée par spectroscopie dans le domaine temporel. La dépendance de la fréquence d émission avec le champ électrique appliqué constitue une preuve directe des oscillations de Bloch. L échelle de Wannier Stark des trous sous pompage optique continu a aussi été observe dans les superréseaux non dopes. Avec l augmentation de la puissance de pompage optique, les pics du photocourant se décalent et leurs formes deviennent asymétriques. L évolution est attribue a l accumulation des porteurs photogénérés dans les deux couches encadrant le superréseau. En outre, pour une puissance de pompage élevée, la bistabilité du photocourant a été également observée.Terahertz (THz) electromagnetic field, which lies in the frequency gap between the infrared and microwave, roughly between 1 THz to 10 THz, is highly desirable for both fundamental research and application. Yet tuneable compact THz sources are still not available. On the other hand, ever since first proposed in 1970, semiconductor superlattice provides new playground for various new technique and devices of tremendous research and application interest. In this thesis, an innovative theme, relying on Bloch oscillations in a dc biased semiconductor superlattice, is explored to realize tunable compact THz source THz Bloch oscillator. For doped superlattice Bloch oscillator, we designed quantum cascade super-superlattice structure to realize Bloch oscillations whilst prohibit electrical domain formation. The designed structures were processed into various waveguide and grating devices for electroluminescence detection using Fourier transform infrared spectroscopy (FTIR). The Bloch gain of semi-insulating surface plasmon waveguide device was also measured using THz time domain spectroscopy. Even though the electroluminescence and gain at THz regime were observed, no direct evidence of Bloch emission was confirmed. For undoped superlattice, the THz emission from Bloch oscillations was observed by time domain spectroscopy. At last, the photocurrent corresponding to heavy hole and Wannier Stark Ladder (WSL) states transitions in undoped superlattice was studied. Under CW laser pumping, the photocurrent as function of the applied voltage showed multiple WSL peaks, which indicated laser induced and controllable negative differential conductance (NDC). With increasing pumping power, the nonlinear NDC regime and bistable states were investigated as well.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF
Interactions and phase behaviors between oleic phase and CO 2 from swelling to miscibility in CO 2 -based enhanced oil recovery (EOR) process: A comprehensive visualization study
No full textFluorinated fused nonacyclic interfacial materials for efficient and stable perovskite solar cells
No full textThree fused-ring n-type semiconductors based on 6,6,12,12-tetrakis(4-hexylphenyl)-indacenobis(dithieno [3,2-b; 2,3-d] thiophene) end-capped with 1,1-dicyanomethylene-3-indanone substituted by different numbers of fluorine atoms (INIC series) are employed as interfacial materials to modify the surface of the perovskite film in inverted planar perovskite solar cells (PSCs). Due to fast interfacial charge extraction and efficient trap passivation, PSCs based on INIC series exhibit a maximum power conversion efficiency of 19.3% without any hysteresis, which is superior to control devices without INIC series (16.6%). Moreover, the strong water-resistance ability of fluorinated INIC significantly enhances the ambient stability of the PSCs. The effects of fluorine atom number on the device performance are discussed.National Natural Science Foundation of China [21673011]SCI(E)ARTICLE4021414-21421
Toxicity studies of tetracycline on Microcystis aeruginosa and Selenastrum capricornutum
No full textThe assays of first exposure and second exposure effects with tetracycline (TC) on the freshwater cyanobacterium Microcystis aeruginosa and chlorophyceae Selenastrum capricornutum were investigated by determining a battery of parameters including algal biomass, chlorophyll fluorescence index Fv/Fm, superoxide dismutase (SOD) and malonaldehyde (MDA) in. this study. In general, TC could significantly inhibit the growth and physiological progress including primary photochemistry and antioxidant system. However, upon the second exposure, the inhibitory effects of TC were decreased compared to the first exposure. And it suggests that Fv/Fm, SOD and MDA were more sensitive than algal biomass. In addition, M. aeruginosa showed stronger survivability than S. capriconutum. (C) 2013 Elsevier B.V. All rights reserved.The assays of first exposure and second exposure effects with tetracycline (TC) on the freshwater cyanobacterium Microcystis aeruginosa and chlorophyceae Selenastrum capricornutum were investigated by determining a battery of parameters including algal biomass, chlorophyll fluorescence index Fv/Fm, superoxide dismutase (SOD) and malonaldehyde (MDA) in. this study. In general, TC could significantly inhibit the growth and physiological progress including primary photochemistry and antioxidant system. However, upon the second exposure, the inhibitory effects of TC were decreased compared to the first exposure. And it suggests that Fv/Fm, SOD and MDA were more sensitive than algal biomass. In addition, M. aeruginosa showed stronger survivability than S. capriconutum. (C) 2013 Elsevier B.V. All rights reserved
Adaptive Amphiphilic Dendrimer-Based Nanoassemblies as Robust and Versatile siRNA Delivery Systems
No full textsiRNA delivery remains a major challenge in RNAi-
based therapy. Here, we report for the first time that an
amphiphilic dendrimer is able to self-assemble into adaptive
supramolecular assemblies upon interaction with siRNA, and
effectively delivers siRNAs to various cell lines, including
human primary and stem cells, thereby outperforming the
currently available nonviral vectors. In addition, this amphi-
philic dendrimer is able to harness the advantageous features of
both polymer and lipid vectors and hence promotes effective
siRNA delivery. Our study demonstrates for the first time that
dendrimer-based adaptive supramolecular assemblies repre-
sent novel and versatile means for functional siRNA delivery,
heralding a new age of dendrimer-based self-assembled drug delivery in biomedical applications
Self-sensitizable neuromorphic device based on adaptive hydrogen gradient
No full textNeuromorphic computing faces long-standing challenges in handling unknown situations beyond the preset boundaries, resulting in catastrophic information loss and model failure. These predicaments arise from the existing brain-inspired hardware's inability to grasp critical information across diverse inputs, often responding passively within unalterable boundaries. Here, we report self-sensitization in perovskite neurons based on an adaptive hydrogen gradient, transcending the conventional fixed response range to autonomously capture unrecognized information. The networks with self-sensitizable neurons work well under unknown environments by reshaping the information reception range and feature salience. It can address the information loss and achieve seamless transition, processing ∼250% more structural information than traditional networks in building detection. Furthermore, the self-sensitizable convolutional network can surpass model boundaries to tackle the data drift accompanying varying inputs, improving accuracy by ∼110% in vehicle classification. The self-sensitizable neuron enables networks to autonomously cope with unforeseen environments, opening new avenues for self-guided cognitive systems.</p
Mastering dendrimer self-assembly for efficient siRNA delivery: from conceptual design to in vivo efficient gene silencing
No full textSelf-assembly is a fundamental concept and a powerful approach in molecular science. However, creating functional materials with the desired properties through self-assembly remains challenging. In this work, through a combination of experimental and computational approaches, we report on the self-assembly of small amphiphilic dendrons into nanosized supramolecular dendrimer micelles with a degree of structural definition similar to traditional covalent high-generation dendrimers. We demonstrate that, with the optimal balance of hydrophobicity and hydrophilicity, one of the self-assembled nanomicellar systems, totally devoid of toxic side effects, is able to deliver small interfering RNA (siRNA) and achieve effective gene silencing both in cells - including the highly refractory human hematopoietic CD34+ stem cells - and in vivo, thus paving the way for future biomedical implementation. This work presents a case study of the concept of generating functional supramolecular dendrimers via self-assembly. The ability of carefully designed and gauged building blocks to assemble into supramolecular structures opens new perspectives on the design of self-assembling nanosystems for complex and functional applications
