catastrophic events, corporate philanthropy, corporate social responsibility, ownership type,
Fig. 1. A still life photograph of our optimized printouts. The thickness of all the pictured samples is 1 cm.Color texture reproduction in 3D printing commonly ignores volumetric light transport (cross-talk) between surface points on a 3D print. Such light di usion leads to signi cant blur of details and color bleeding, and is particularly severe for highly translucent resin-based print materials. Given their widely varying scattering properties, this cross-talk between surface points strongly depends on the internal structure of the volume surrounding each surface point. Existing scattering-aware methods use simpli ed models for light di usion, and often accept the visual blur as an immutable property of the print medium. In contrast, our work counteracts heterogeneous scattering to obtain the impression of a crisp albedo texture on top of the 3D print, by optimizing for a fully volumetric material distribution that preserves the target appearance. Our method employs an e cient numerical optimizer on top of a general Monte-Carlo simulation of heterogeneous scattering, supported by a practical calibration procedure to obtain scattering parameters from a given set of printer materials. Despite the inherent translucency of the medium, we reproduce detailed surface textures on 3D prints. We evaluate our system using a commercial, ve-tone 3D print process and compare against the printer's native color texturing mode, demonstrating *Oskar Elek and Denis Sumin share the rst authorship of this work. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for pro t or commercial advantage and that copies bear this notice and the full citation on the rst page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior speci c permission and/or a fee. Request permissions from permissions@acm.org. © 2017 ACM. 0730-0301/2017/11-ART241 $15.00 DOI: 10.1145/3130800.3130890 that our method preserves high-frequency features well without having to compromise on color gamut.
In this work, the fundamental mechanism of ultrabright fluorescence from surface-modified colloidal silicon quantum dots is investigated in depth using ultrafast spectroscopy. The underlying energy band structure corresponding to such highly efficient direct bandgap-like emissions in our surface-modified silicon quantum dots is unraveled by analyzing the transient optical spectrum, which demonstrates the significant effect of surface molecular engineering. It is observed that special surface modification, which creates novel surface states, is responsible for the different emission wavelengths and the significant improvement in the photoluminescence quantum yields. Following this essential understanding, surface-modified silicon quantum dots with deep blue to orange emission are successfully prepared without changing their sizes. Keywords: quantum confinement; silicon quantum dots; surface molecular engineering; ultrafast spectroscopy; wave function modification INTRODUCTIONCrystalline silicon has been the most important semiconductor material in the modern electronics industry due to its excellent electronic properties. However, as a well-known indirect bandgap semiconductor, the optical properties of crystalline silicon are relatively poor, which limits its applications in silicon photonics. To pursue the desired optical performance in silicon materials, nanostructured silicon objects with enhanced photoluminescence (PL) have attracted increasing interest. 1213 Most notably, due to the three-dimensional quantum confinement effect in silicon nanocrystals (Si NCs), the momentum conservation rule is relaxed, and the spatial distributions of photogenerated exciton wave functions tend to extend to the surface of nanoparticles, which provides an efficient approach to manipulate the energy structure of silicon. 14218 Thus, the excitonic emission from Si NCs are usually thought to follow three models: (i) 'direct' transition from a quantization-related bandgap; (ii) indirect approaches, i.e., with the help of other emission centers; and (iii) surface and/or strain engineering. 19 For the 'direct' approach, the observed size-dependent PL behavior in Si NCs can be well explained by the quantum confinement effect. However, such Si NCs can hold strong PL only in the deep red region with limited stability, and their PL lifetimes from these 'direct'
We examine the financial health and performance of reverse mergers (RMs) that became active on U.S. stock markets between 2001 and 2010, particularly those from China (around 85 percent of all foreign RMs). As a group, RMs are early-stage companies that typically trade over the counter. However, Chinese RMs (CRMs) tend to be more mature and less speculative than either their U.S. counterparts or a group of exchange-industry-size-matched firms. As a group, CRMs outperformed their matched peers from inception through the end of 2013, even after including most of the firms accused of accounting fraud. CRMs that receive private investment in public equity (PIPE) financing from sophisticated investors perform particularly well. Overall, despite the negative publicity, we find little evidence that CRMs are inherently toxic investments. Our results shed light on the risk-performance trade-off for CRMs, as well as the delicate balance between credibility and access in well-functioning markets. JEL Classifications: G34; M41; N20
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