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Chiu P.L.,Rutgers University | Mastrogiovanni D.D.T.,Rutgers University | Wei D.,Carl Zeiss GmbH | Louis C.,Irvington High School | And 7 more authors.
Journal of the American Chemical Society | Year: 2012

Currently the preferred method for large-scale production of solution-processable graphene is via a nonconductive graphene oxide (GO) pathway, which uncontrollably cuts sheets into small pieces and/or introduces nanometer-sized holes in the basal plane. These structural changes significantly decrease some of graphenes remarkable electrical and mechanical properties. Here, we report an unprecedented fast and scalable approach to avoid these problems and directly produce large, highly conductive graphene sheets. This approach intentionally excludes KMnO 4 from Hummers methods and exploits aromatic oxidation by nitronium ions combined with the unique properties of microwave heating. This combination promotes rapid and simultaneous oxidation of multiple non-neighboring carbon atoms across an entire graphene sheet, thereby producing only a minimum concentration of oxygen moieties sufficient to enable the separation of graphene sheets. Thus, separated graphene sheets, which are referred to as microwave-enabled low-oxygen graphene, are thermally stable and highly conductive without requiring further reduction. Even in the absence of polymeric or surfactant stabilizers, concentrated dispersions of graphene with clean and well-separated graphene sheets can be obtained in both aqueous and organic solvents. This rapid and scalable approach produces high-quality graphene sheets of low oxygen content, enabling a broad spectrum of applications via low-cost solution processing. © 2012 American Chemical Society.


Weinersmith K.L.,University of California at Davis | Warinner C.B.,Dos Pueblos High School | Warinner C.B.,Cambridge College | Tan V.,Irvington High School | And 7 more authors.
Integrative and Comparative Biology | Year: 2014

For trophically transmitted parasites that manipulate the phenotype of their hosts, whether the parasites do or do not experience resource competition depends on such factors as the size of the parasites relative to their hosts, the intensity of infection, the extent to which parasites share the cost of defending against the host's immune system or manipulating their host, and the extent to which parasites share transmission goals. Despite theoretical expectations for situations in which either no, or positive, or negative density-dependence should be observed, most studies document only negative density-dependence for trophically transmitted parasites. However, this trend may be an artifact of most studies having focused on systems in which parasites are large relative to their hosts. Yet, systems are common where parasites are small relative to their hosts, and these trophically transmitted parasites may be less likely to experience resource limitation. We looked for signs of density-dependence in Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB), two manipulative trematode parasites infecting wild-caught California killifish (Fundulus parvipinnis). These parasites are small relative to killifish (suggesting resources are not limiting), and are associated with changes in killifish behavior that are dependent on parasite-intensity and that increase predation rates by the parasites' shared final host (indicating the possibility for cost sharing). We did not observe negative density-dependence in either species, indicating that resources are not limiting. In fact, observed patterns indicate possible mild positive density-dependence for EUHA. Although experimental confirmation is required, our findings suggest that some behavior-manipulating parasites suffer no reduction in size, and may even benefit when crowded by conspecifics. © The Author 2014.


Seo D.-M.,Korea University | Kim N.-H.,Korea University | Lee D.-H.,Korea University | Kim J.-D.,Korea University | In J.S.,Irvington High School
International Journal of Multimedia and Ubiquitous Engineering | Year: 2012

Many researchers in the field of requirements engineering are now focusing on eliciting requirements only from market influencers, that is, people who have a great influence on the market success of products. However, acting on the requirements expressed by customers without validating them can cause a product to fail in the market. Therefore, the importance of a requirement proposed by a customer should be validated by various other customers. Social Network Services (SNSs) are an important tool for validating customer requirements. They offer various advantages, such as ease of access and ease of use, and the diversity of their users. We therefore propose a method for analyzing the impact of customer requirements, based on SNSs. Our proposed method considers various factors, such as the time a customer spends on transmitting messages, the number of customers receiving the messages, and the opinions expressed in the messages. The method makes it possible to evaluate the impact of a customer's requirements and to support a software project through prioritizing these requirements.


Kirby E.N.,California Institute of Technology | Guo M.,Irvington High School | Guo M.,Stanford University | Zhang A.J.,Harker School | And 6 more authors.
Astrophysical Journal | Year: 2015

We present carbon abundances of red giants in Milky Way (MW) globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above , which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of SNe Ia at higher metallicities. We also identified 11 very carbon-rich giants (eight previously known) in three dSphs. However, our selection biases preclude a detailed comparison to the carbon-enhanced fraction of the MW stellar halo. Nonetheless, the stars with in dSphs follow a different [C/Fe] track with [Fe/H] than the halo stars. Specifically, [C/Fe] in dSphs begins to decline at lower [Fe/H] than in the halo. The difference in the metallicity of the [C/Fe] "knee" adds to the evidence from [α/Fe] distributions that the progenitors of the halo had a shorter timescale for chemical enrichment than the surviving dSphs. © 2015. The American Astronomical Society. All rights reserved..


Kirby E.N.,California Institute of Technology | Guhathakurta P.,University of California at Santa Cruz | Zhang A.J.,Harker School | Zhang A.J.,Stanford University | And 6 more authors.
Astrophysical Journal | Year: 2016

Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ±0.1)% for the RGB, (1.6 ±1.1)% for the AGB, and (0.3 ±0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval. © 2016. The American Astronomical Society. All rights reserved..

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