Topology-constrained Synthesis of Vector Patterns

International audienceDecorative patterns are observed in many forms of art, typically enriching the visual aspect of otherwise simple shapes. Such patterns are especially difficult to create, as they often exhibit intricate structural details and at the same time have to precisely match the size and shape of the underlying geometry. In the field of Computer Graphics, several approaches have been proposed to automatically synthesize a decorative pattern along a curve, from an example. This empowers non expert users with a simple brush metaphor, allowing them to easily paint complex structured decorations.We extend this idea to the space of design and fabrication. The major challenge is to properly account for the topology of the produced patterns. In particular, our technique ensures that synthesized patterns will be made of exactly one connected component, so that once printed they form a single object. To achieve this goal we propose a two steps synthesis process, first synthesizing the topology of the pattern and later synthesizing its exact geometry. We introduce topology descriptors that efficiently capture the topology of the pattern synthesized so far.We propose several applications of our method, from designing objects using synthesized patterns along curves and within rectangles, to the decoration of surfaces with a dedicated smooth frame interpolation. Using our technique, designers paint structured patterns that can be fabricated into solid, tangible objects, creating unusual and surprising designs of lamps, chairs and laces from examples

Mixed-use residential development and its effects on the travel behaviour of residents: findings from casestudies in Beijing

published_or_final_versionabstractArchitectureMasterMaster of Philosoph

Sensor cascading fault estimation and control for hypersonic flight vehicles based on a multidimensional generalized observer

This study presents a sensor cascading fault estimation and fault-tolerant control (FTC) for a nonlinear Takagi-Sugeno fuzzy model of hypersonic flight vehicles. Sensor cascading faults indicate the occurrence of source fault will cause another fault and the interval between them is really short, which makes it difficult to handle them in succession. A novel multidimensional generalized observer is used to estimate faults by integrating constant offset and time-varying gain faults. Then, a fault-tolerant controller is used to solve system nonlinearity and sensor fault problems. The observer and controller satisfy the performance index and are robust to external disturbances. A sufficient condition for the existence of observer and controller is derived on the basis of Lyapunov theory. Simulation results indicate the effectiveness of the proposed fault estimation and FTC scheme

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Enhanced conversion efficiency for Si nanowire–organic hybrid solar cells through the incorporation of organic small molecule

We demonstrate high-efficiency hybrid solar cells based on heterojunctions formed between n-type silicon nanowires (SiNWs) and p-type organic semiconductors fabricated using a simple solution-based approach. Two types of devices have been fabricated with different organic materials used, namely poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and a small molecule, 2,2',7,7'-tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD). The cells are characterized and compared in terms of their physical characteristics and photovoltaic performance. Using SiNWs of the same length of 0.35 µm, it is found that the SiNWs/Spiro cells exhibit a power conversion efficiency of 10.3%, which is higher than the 7.7% of SiNWs/PEDOT cells. The results are interpreted in terms of the ability of the two organic semiconductors to fill the gaps between the SiNWs and the optical reflectance of the samples. The degradation of the SiNWs/Spiro cells is also studied and presented

High efficiency planar Si/organic heterojunction hybrid solar cells

We present an efficient hybrid solar cell based on poly (3,4-ethylene-dioxythiophene):polystyrenesulfonate and planar Si with (100) and (111) orientations. The effect of Si surface native oxide on cell performance is studied. Compared to cell with hydrogen-terminated Si surface, the cell with oxygen-terminated Si surface reveals a 530-fold increase in power conversion efficiency (PCE) from 0.02% to 10.6%. The formation of SiOx-Si bonds poses a net positive surface dipole which leads to a favorable band alignment for charge separation. However, thicker oxide degrades cell performance due to higher series resistance. This study demonstrates the highest PCE reported to-date in this field.Published versio

Si nanowires organic semiconductor hybrid heterojunction solar cells toward 10% efficiency

High-efficiency hybrid solar cells are fabricated using a simple approach of spin coating a transparent hole transporting organic small molecule, 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) on silicon nanowires (SiNWs) arrays prepared by electroless chemical etching. The characteristics of the hybrid cells are investigated as a function of SiNWs length from 0.15 to 5 μm. A maximum average power conversion efficiency of 9.92% has been achieved from 0.35 μm length SiNWs cells, despite a 12% shadowing loss and the absence of antireflective coating and back surface field enhancement. It is found that enhanced aggregations in longer SiNWs limit the cell performance due to increased series resistance and higher carrier recombination in the shorter wavelength region. The effects of the Si substrate doping concentrations on the performance of the cells are also investigated. Cells with higher substrate doping concentration exhibit a significant drop in the incident photons-to-current conversion efficiency (IPCE) in the near infrared region. Nevertheless, a promising short circuit current density of 19 mA/cm2 and IPCE peak of 57% have been achieved for a 0.9 μm length SiNWs cell fabricated on a highly doped substrate with a minority-carrier diffusion length of only 15 μm. The results suggest that such hybrid cells can potentially be realized using Si thin films instead of bulk substrates. This is promising towards realizing low-cost and high-efficiency SiNWs/organic hybrid solar cells

Design guideline for Si/organic hybrid solar cell with interdigitated back contact structure

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11.3% efficient planar Si-PEDOT : PSS hybrid solar cell with a thin interfacial oxide

Hybrid solar cells are fabricated based on heterojunction between planar n-type Si and a p-type polymer, poly (3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT: PSS). The effect of hydrogen-terminated (H-Si) and oxide-terminated (SiOx-Si) Si surface on the cell performance are investigated. Compared to cells with H-Si surface that exhibits a power conversion efficiency (PCE) of 0.04%, the PCE of the cells with SiOx-Si surface is boosted significantly to 11.3%. It is also found that the SiOx-Si cell exhibits a much better diode rectifying behavior and the SiOx-Si surface bonding results in a favorable band alignment in the Si/PEDOT interface for photo-excited carrier separation