In situ nanocompression testing of irradiated copper.

Increasing demand for energy and reduction of carbon dioxide emissions has revived interest in nuclear energy. Designing materials for radiation environments necessitates a fundamental understanding of how radiation-induced defects alter mechanical properties. Ion beams create radiation damage efficiently without material activation, but their limited penetration depth requires small-scale testing. However, strength measurements of nanoscale irradiated specimens have not been previously performed. Here we show that yield strengths approaching macroscopic values are measured from irradiated ~400 nm-diameter copper specimens. Quantitative in situ nanocompression testing in a transmission electron microscope reveals that the strength of larger samples is controlled by dislocation-irradiation defect interactions, yielding size-independent strengths. Below ~400 nm, size-dependent strength results from dislocation source limitation. This transition length-scale should be universal, but depends on material and irradiation conditions. We conclude that for irradiated copper, and presumably related materials, nanoscale in situ testing can determine bulk-like yield strengths and simultaneously identify deformation mechanisms

Growth of Indium Nitride Quantum Dots by Molecular Beam Epitaxy

Over the last decade, the evolution of the global consciousness in response to decreasing environmental conditions from global warming and pollution has led to an outcry for finding new alternative/clean methods for harvesting energy and determining ways to minimize energy consumption. III-nitride materials are of interest for optoelectronic and electronic device applications such as high efficiency solar cells, solid state lighting (LEDs), and blue laser (Blu-ray Technology) applications. The wide range of direct band gaps covered by its alloys (0.7eV-6.2eV) best illustrates the versatility of III-nitride materials. This wide range has enabled applications extending from the ultraviolet to the near infrared. This study investigates the processes by which InN quantum dots (QDs) form through molecular beam epitaxy (MBE) growth in Nitrogen-Rich and Metal-Rich growth environments. Structural characterization was performed using Atomic Force Microscopy. Statistical analysis was performed on both growth environments, Metal-Rich and Nitrogen-Rich, to observe changes in nucleation density, QD height and diameter, volume of InN, and the contact angle between the QDs and the growth surface. To further understand the growth environments, the system was analyzed as functions of growth temperature, deposition time, and deposition rate. Under Nitrogen-Rich growth environment, it was found that the growth of InN QDs follows typical Stranski-Krastinov (SK), heterogeneous nucleation theory. However, due to the existence of an excess indium adlayer, the Metal-Rich growth condition changes the development of the InN QDs. The results of this investigation are presented herein. A cursory investigation in the optical response of both growth environments was performed. The optical response was characterized through photoluminescence (PL) spectroscopy with a transition at 730 nm for Metal-Rich InN QDs using a two-step GaN capping procedure

Integration and Conventional Systems at STAR

At the beginning of the design and construction of the STAR Detector, the collaboration assigned a team of physicists and engineers the responsibility of coordinating the construction of the detector. This group managed the general space assignments for each sub-system and coordinated the assembly and planning for the detector. Furthermore, as this group was the only STAR group with the responsibility of looking at the system as a whole, the collaboration assigned it several tasks that spanned the different sub-detectors. These items included grounding, rack layout, cable distribution, electrical, power and water, and safety systems. This paper describes these systems and their performance.Comment: 17 pages, 6 figures, Contribution to a NIM Volume Dedicated to the Detectors and the Accelerator at RHI

Selective Lanthanide Sensing with Gold Nanoparticles and Hydroxypyridinone Chelators.

The octadentate hydroxypyridinone chelator 3,4,3-LI(1,2-HOPO) is a promising therapeutic agent because of its high affinity for f-block elements and noncytotoxicity at medical dosages. The interaction between 3,4,3-LI(1,2-HOPO) and other biomedically relevant metals such as gold, however, has not been explored. Gold nanoparticles functionalized with chelators have demonstrated great potential in theranostics, yet thus far, no protocol that combines 3,4,3-LI(1,2-HOPO) and colloidal gold has been developed. Here, we characterize the solution thermodynamic properties of the complexes formed between 3,4,3-LI(1,2-HOPO) and Au3+ ions and demonstrate how under specific pH conditions the chelator promotes the growth of gold nanoparticles, acting as both reducing and stabilizing agent. 3,4,3-LI(1,2-HOPO) ligands on the nanoparticle surface remain active and selective toward f-block elements, as evidenced by gold nanoparticle selective aggregation. Finally, a new colorimetric assay capable of reaching the detection levels necessary for the quantification of lanthanides in waste from industrial processes is developed based on the inhibition of particle growth by lanthanides

Stigma resistance at the personal, peer, and public levels: A new conceptual model.

Stigma resistance is consistently linked with key recovery outcomes, yet theoretical work is limited. This study explored stigma resistance from the perspective of individuals with serious mental illness (SMI). Twenty-four individuals with SMI who were either peer-service providers (those with lived experience providing services; N = 14) or consumers of mental health services (N = 10) engaged in semistructured interviews regarding experiences with stigma, self-stigma, and stigma resistance, including key elements of this process and examples of situations in which they resisted stigma. Stigma resistance is an ongoing, active process that involves using one’s experiences, knowledge, and sets of skills at the (1) personal, (2) peer, and (3) public levels. Stigma resistance at the personal level involves (a) not believing stigma or catching and challenging stigmatizing thoughts, (b) empowering oneself by learning about mental health and recovery, (c) maintaining one’s recovery and proving stigma wrong, and (d) developing a meaningful identity apart from mental illness. Stigma resistance at the peer level involves using one’s experiences to help others fight stigma and at the public level, resistance involved (a) education, (b) challenging stigma, (c) disclosing one’s lived experience, and (d) advocacy work. Findings present a more nuanced conceptualization of resisting stigma, grounded in the experiences of people with SMI. Stigma resistance is an ongoing, active process of using one’s experiences, skills, and knowledge to develop a positive identity. Interventions should consider focusing on personal stigma resistance early on and increasing the incorporation of peers into services

Performance and Relative Incentive Pay: The Role of Social Preferences

__Abstract__ Under relative performance pay, other-regarding workers internalize the negative externality they impose on other workers. In one form -increased own effort reduces others' payoffs- this results in other-regarding individuals depressing efforts. In another form punishment reduces the payoff of other workers- groups with other-regarding individuals feature higher efforts because it is more difficult for these individuals to sustain low-effort (collusive) outcomes. We explore these effects experimentally and find other-regarding workers tend to depress efforts by 15% on average. However, selfish workers are nearly three times more likely to lead workers to coordinate on minimal efforts when communication is possible. Hence, the social preferences composition of a team of workers has nuanced consequences on efforts

Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 208 (2017): 102-118, doi:10.1016/j.gca.2017.03.021.We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41-71 %) of the lake DOC relative to HMW DOC (10-13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25 to 43‰) and HMW DOC (Δ14C = 22 to 32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ~ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270-2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.This work was funded by the National Science Foundation OCE 0825600 to E.C.M. and J.P.W., a graduate student internship fellowship to P.K.Z by National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487), and the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution to P.K.Z, with funding provided by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487)