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ABSTRACT. We conducted a study of relative gas composition changes of CO2, CO and CH4 during the formation of graphite targets using different temperatures, catalysts and methods. Reduction with H2 increases the reaction rate without compromising the quality of the AMS target produced. Methane is produced at virtually any temperature, and the amount produced is greater at very low temperatures. The reduction of CO to graphite is very slow when H2 is not included in the reaction.

Magnetic resonance imaging (MRI) has become one of the most important diagnosis tools available in medicine. Typically MRI is not capable of sensing biochemical activities. However, recently emerged activatable MRI contrast agents (CAs), whose relaxivity is variable in response to a specific parameter change in the surrounding physiological microenvironment, potentially allow for MRI to indicate biological processes. Among the various factors influencing the relaxivity of a CA, the number of inner-sphere water molecules (q) directly coordinated to the metal center, the residence time of the coordinated water molecule (τm), and the rotational correlation time representing the molecular tumbling time of a complex (τR) contribute strongly to the relaxivity of an activatable CA. Tuning the ligand structure and properties has been the subject of intensive research for activatable MR CA designs. This review summarizes a variety of activatable MRI CAs sensitive to common variables in microenvironment in vivo, i.e., pH, luminescence, metal ions, redox, and enzymes, etc., with emphasis on the influence of ligand design on parameters q, τm, and τR.

A reversible T2 contrast agent consisting of cross-linked anionic dextran coated iron oxide nanoparticles covalently coupled to a light-sensitive spiropyran (SP)/merocyanine (MC) motif was synthesized and characterized. In aqueous solution, light induced isomerization of the molecular switches between the hydrophobic SP isomer and hydrophilic MC isomer directs the aggregation and dispersion of the nanoparticles, respectively. When in the dark, where the MC form dominates, the probe has a T2 relaxation time of 37.09 ms (60 MHz, 37 degrees C) and two size populations at 70 and 540 nm. After irradiation with visible light, the T2 relaxation time is shortened 33.7%, and the size correspondingly shifts to a single population at 520 nm upon aggregation. This "smart" T2 agent provides the advantage of reversibility which may enable dynamic monitoring with MRI. In addition, the light responsiveness of this agent suggests the potential to employ them as MRI gene reporters for the luciferase expression system.

Currently, magnetic iron oxide nanoparticles are the only nanosized magnetic resonance imaging (MRI) contrast agents approved for clinical use, yet commercial manufacturing of these agents has been limited or discontinued. Though there is still widespread demand for these particles both for clinical use and research, they are difficult to obtain commercially, and complicated syntheses make in-house preparation unfeasible for most biological research labs or clinics. To make commercial production viable and increase accessibility of these products, it is crucial to develop simple, rapid and reproducible preparations of biocompatible iron oxide nanoparticles. Here, we report a rapid, straightforward microwave-assisted synthesis of superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles were produced in two hydrodynamic sizes with differing core morphologies by varying the synthetic method as either a two-step or single-step process. A striking benefit of these methods is the ability to obtain swift and consistent results without the necessity for air-, pH- or temperature-sensitive techniques; therefore, reaction times and complex manufacturing processes are greatly reduced as compared to conventional synthetic methods. This is a great benefit for cost-effective translation to commercial production. The nanoparticles are found to be superparamagnetic and exhibit properties consistent for use in MRI. In addition, the dextran coating imparts the water solubility and biocompatibility necessary for in vivo utilization.

A redox-and light-sensitive, T 1 -weighted magnetic resonance imaging (MRI) contrast agent which tethers a spiropyran(SP)/merocyanine(MC) motif to a Gd-DO3A moiety was synthesized and characterized. When in the dark, the probe is in its MC form which has an r 1 relaxivity of 2.51 mM −1 s −1 (60MHz, 37°C). After irradiation with visible light or mixing with NADH, the probe experiences an isomerization and the r 1 relaxivity decreased 18% and 26%, respectively. Additionally, the signal intensity in MRI showed an observable decrease after the compound was mixed with NADH.

While positive emotion can be conceptualized broadly as a response to the potential for reward, the environment offers different kinds of rewards, and these are best approached in somewhat different ways. A functional approach to positive emotion differentiation distinguishes among several different types of rewards with strong implications for adaptive fitness and posits the existence of "discrete" positive emotions that promote an adaptive response to each reward. A taxonomy of eight positive emotions, dubbed the "PANACEAS" taxonomy based on an acronym of the first letter of each of the eight constructs, is presented as an example of this approach. Positive emotion constructs defined through functional analyses are useful for guiding empirical research, especially for identifying prototypical eliciting stimuli, and generating hypotheses about the implications of different positive emotions for a variety of outcomes. Research findings are reviewed that support the importance of positive emotion differentiation in understanding the effects of positive emotions on cognition, physiology, and behavior. Advantages of the functional approach are discussed, as well as implications of the approach for evaluating major theories of the structure of emotion. Positive Emotion Differentiation: A Functional ApproachImagine that you are in each the following situations: waiting eagerly for a cool drink you just ordered on a hot afternoon; stretching out on your couch after a long day and a satisfying dinner; holding your new baby niece or nephew in your arms; making eye contact with a sexy person you just met at a party; having a loved one care for and comfort you when you're sick; laughing at a joke told by a colleague; and gazing at the view from a high ridge on a mountain. Each of these situations is pleasant. Each offers potential for reward. Yet the nature of the reward varies considerably from situation to situation, and you take advantage of that reward by somewhat different means. While there is undoubtedly overlap in the emotions felt in each of these situations, there are important differences as well.For the most part, theories of positive emotion have not emphasized the possibility that different positive emotions might have qualitatively distinct implications for cognition, physiological responding, motivation, and behavior, or offered a strong basis for hypotheses about differential effects. A functional approach to positive emotion differentiation helps to address this gap. Analyses of the adaptive functions of "discrete" negative emotion states have long been used to guide research on emotional responding (e.g., Lazarus, 1991), producing a rich body of empirical work. In this paper, we discuss the advantages of using functional analysis to define discrete positive emotion constructs as well; present a taxonomy of eight positive emotions, labeled with the acronym "PANACEAS", that serves as an example of the functional approach; and offer several examples of research guided by the PANACEAS model and simi...

ABSTRACT. During the four years the Sample Preparation Laboratory (SPL) at the National Ocean Sciences Accelerator Mass Spectrometer (NOSAMS) Facilty has been in operation we have accumulated much data from which we can assess our progress. We evaluate our procedural blanks here and describe modifications in our procedures that have improved our analyses of older samples. In the SPL, we convert three distinct types of samples-seawater, CaCO3 and organic carbon-to CO2 prior to preparing graphite for the accelerator and have distinct procedural blanks for each procedure. Dissolved inorganic carbon (ECO2) is extracted from acidified seawater samples by sparging with a nitrogen carrier gas. We routinely analyze "line blanks" by processing CO2 from a 14C-dead source through the entire stripping procedure. Our hydrolysis blank, IAEA C-1, is prepared by acidifying in vacuo with 100% H3PO4 at 60°C overnight, identical to our sample preparation. We use a dead graphite, NBS-21, or a commercially available carbon powder for our organic combustion blank; organic samples are combusted at 850°C for S h using CuO to provide the oxidant. Analysis of our water stripping data suggests that one step in the procedure contributes the major portion of the line blank. At present, the contribution from the line blank has no effect on our seawater analyses (fraction modern (fm) between 0.7 and 1.2). Our hydrolysis blanks can have an fm value as low as 0.0006, but are more routinely between 0.0020 and 0.0025. The fm of our best organic combustion blanks is higher than those routinely achieved in other laboratories and we are currently altering our methods to reduce it.