Seoul National University

About: Seoul National University is a education organization based out in Seoul, South Korea. It is known for research contribution in the topics: Population & Catalysis. The organization has 65879 authors who have published 138759 publications receiving 3715170 citations. The organization is also known as: SNU & Seoul-dae.

Controlling the influence of Auger recombination on the performance of quantum-dot light-emitting diodes

Abstract: Development of light-emitting diodes (LEDs) based on colloidal quantum dots is driven by attractive properties of these fluorophores such as spectrally narrow, tunable emission and facile processibility via solution-based methods. A current obstacle towards improved LED performance is an incomplete understanding of the roles of extrinsic factors, such as non-radiative recombination at surface defects, versus intrinsic processes, such as multicarrier Auger recombination or electron-hole separation due to applied electric field. Here we address this problem with studies that correlate the excited state dynamics of structurally engineered quantum dots with their emissive performance within LEDs. We find that because of significant charging of quantum dots with extra electrons, Auger recombination greatly impacts both LED efficiency and the onset of efficiency roll-off at high currents. Further, we demonstrate two specific approaches for mitigating this problem using heterostructured quantum dots, either by suppressing Auger decay through the introduction of an intermediate alloyed layer, or by using an additional shell that impedes electron transfer into the quantum dot to help balance electron and hole injection.

A terahertz metamaterial with unnaturally high refractive index

Abstract: Controlling the electromagnetic properties of materials, going beyond the limit that is attainable with naturally existing substances, has become a reality with the advent of metamaterials. The range of various structured artificial 'atoms' has promised a vast variety of otherwise unexpected physical phenomena, among which the experimental realization of a negative refractive index has been one of the main foci thus far. Expanding the refractive index into a high positive regime will complete the spectrum of achievable refractive index and provide more design flexibility for transformation optics. Naturally existing transparent materials possess small positive indices of refraction, except for a few semiconductors and insulators, such as lead sulphide or strontium titanate, that exhibit a rather high peak refractive index at mid- and far-infrared frequencies. Previous approaches using metamaterials were not successful in realizing broadband high refractive indices. A broadband high-refractive-index metamaterial structure was theoretically investigated only recently, but the proposed structure does not lend itself to easy implementation. Here we demonstrate that a broadband, extremely high index of refraction can be realized from large-area, free-standing, flexible terahertz metamaterials composed of strongly coupled unit cells. By drastically increasing the effective permittivity through strong capacitive coupling and decreasing the diamagnetic response with a thin metallic structure in the unit cell, a peak refractive index of 38.6 along with a low-frequency quasi-static value of over 20 were experimentally realized for a single-layer terahertz metamaterial, while maintaining low losses. As a natural extension of these single-layer metamaterials, we fabricated quasi-three-dimensional high-refractive-index metamaterials, and obtained a maximum bulk refractive index of 33.2 along with a value of around 8 at the quasi-static limit.

Individual-Level Factors and Organizational Performance in Government Organizations

Abstract: In this journal, Rainey and Steinbauer proposed a theory of effective government organizations, and Brewer and Selden conducted an empirical study with data from the 1996 Merit Principles Survey that confirmed most hypothesized relationships in the theoretical model of organizational performance. Following these studies, this study focuses only on the individual-level factors, such as job satisfaction, affective commitment, public service motivation, and organizational citizenship behavior. It empirically tests the effects of these variables on organizational performance in the public sector of Korea. When the survey data of 1,739 public employees in government agencies were analyzed, the hypothesized relationships in the proposed model were confirmed. I discuss the survey results in light of previous studies, especially those of Brewer and Selden. In this journal, Rainey and Steinbauer (1999) proposed a theory of effective government organizations, urging that this theory be tested empirically; Brewer and Selden (2000) conducted an empirical study with data from the 1996 Merit Principles Survey and confirmed most hypothesized relationships in the theoretical model of organizational performance. In those studies, both individual-level and organization-level factors are involved in the theoretical models; thus each level was not fully examined, and some important factors remain to be considered. Brewer and Selden (2000) inspire me to pursue further evidence about whether the individual attitudes and behaviors of public employees may affect government performance. Popovich defined high-performance organizations as "groups of employees who produce desired goods or services at higher quality with the same or fewer resources" (1998, 11). Good public employees may be imagined to have such characteristics as high satisfaction with their jobs, high commitment to the organization, high motivation to serve the public, and strong intentions to work for the organization willingly and devotedly. I assume that public employees with these characteristics will contribute to organizational performance and thus that individual-level factors will positively affect organizational performance. I will discuss the individual-level factors and develop the model that relates I would like to thank the anonymous reviewers for the useful suggestions and comments provided through the review process. Address correspondence to the author at smook@snut.ac.kr. doi:l 0.1 093/jopart/mui013 Advance Access publication on December 16, 2004 Journal of Public Administration Research and Theory, Vol. 15, no. 2 ? 2005 Journal of Public Administration Research and Theory, Inc.; all rights reserved. This content downloaded from 157.55.39.186 on Sun, 09 Oct 2016 04:20:00 UTC All use subject to http://about.jstor.org/terms 246 Journal of Public Administration Research and Theory Figure 1 Theoretical Model of Individual-Level Factors and Organizational Performance

Elliptic flow of identified hadrons in [formula presented] collisions at [formula presented]

Abstract: The anisotropy parameter (v(2)), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in Au+Au collisions at roots(NN)=200 GeV for identified and inclusive charged particle production at central rapidities (eta 2 GeV/c, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.