The deuteron NMR Hahn echo decay in polyethylene oxide melts

The deuteron transverse relaxation properties of polyethylene oxide melts of four different molecular weights, covering the range from the onset of entanglements to the regime of fully entangled chains, are investigated using Hahn echo decays over an extensive time interval up to ten times the effective transverse spin relaxation time. The results are compared to predictions based on the Rouse and reptation formalisms, taking into account the dynamical heterogeneity of linear polymer chains produced by the end segments. The experimental results can be described qualitatively by a combination of both models, with the contribution of reptation dynamics increasing with growing chain length. The transition is continuous, rather than being characterized by sharp regime boundaries. Up to a molecular weight of 300.000 g/mol, the predicted limit of pure reptation dynamics is not yet reached. Quantitative deviations from the predicted decays as computed by numerical procedures become observable toward the long-time limit of the Hahn echo decays and are being discussed in terms of shortcomings of the available reptation theories

Anything for a Cheerio: Brown Capuchins (\u3cem\u3eSapajus [Cebus] apella\u3c/em\u3e) Consistently Coordinate in an Assurance Game for Unequal Payoffs

Unequal outcomes disrupt cooperation in some situations, but this has not been tested in the context of coordination in economic games. To explore this, we tested brown capuchins (Sapajus [Cebus] apella) on a manual version of the Stag Hunt (or Assurance) Game, in which individuals sequentially chose between two options, Stag or Hare, and were rewarded according to their choices and that of their partner. Typically, coordination on Stag results in an equal highest payout, whereas coordinating on Hare results in a guaranteed equal but lower payoff and uncoordinated play results in the lowest payoff when playing Stag. We varied this structure such that one capuchin received double the rewards for the coordinated Stag outcome; thus, it was still both animals\u27 best option, but no longer equally rewarding. Despite the inequality, capuchins coordinated on Stag in 78% of trials, and neither payoff structure nor their partner\u27s choice impacted their decision. Additionally, there was no relationship between self-scratching, a measure of stress in capuchins, and choices. After completing the study, we discovered our reward, cheerios, was sufficiently valuable that in another study, capuchins never refused it, so post hoc we repeated the study using a lower value reward, banana flavored pellets. Capuchins completed only 26% of the pellet trials (compared to 98% with cheerios), constraining our ability to interpret the results, but nonetheless the monkeys showed a decrease in preference for Stag, particularly when they received fewer rewards for the coordinated Stag outcome. These results reinforce capuchins\u27 ability to find coordinated outcomes in the Stag Hunt game, but more work is needed to determine whether the monkeys did not mind the inequality or were unwilling to sacrifice a highly preferred food to rectify it. In either case, researchers should carefully consider the impact of their chosen rewards on subjects\u27 choices

Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.Comment: 8 pages, 6 figur

Experimental determination of the solubilities of CO2 and CH4 in diethyl methylphosphonate

The phase behavior of the binary systems consisting of the organic solvent diethyl methylphosphonate (DEMP) and the gases carbon dioxide (CO2) and methane (CH4) is experimentally studied. A synthetic method is used to measure the solubilities. Bubble-point pressures of the system DEMP + CO2 are reported for CO2 concentrations ranging from (15.40 to 86.44) mole % and within a temperature range of (283.4 to 338.1) K and compared to the limited experimental data in the literature. Also, bubble-point pressures of the system DEMP + CH4 are reported for CH4 concentrations ranging from (5.17 to 15.30) mole % and within a temperature range of (283.2 to 358.5) K, which have never been measured before. The solubilities of CH4 are much lower than the solubilities of CO2 in DEMP. Moreover, the temperature has a much larger influence on the CO2 solubility in DEMP compared to the effect of temperature on the CH4 solubility

Molecular Dynamics and Proton Hyperpolarization via Synthetic and Crude Oil Porphyrin Complexes in Solid and Solution States

The use of vanadyl porphyrins either in synthetic compounds or naturally occurring in asphaltenes is investigated as a source of proton hyperpolarization via dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) experiments. The features of dynamics and location of the vanadyl VO2+ complex in aggregates within the oil asphaltene molecules are studied by means of DNP, electron paramagnetic resonance (EPR), and NMR field cycling relaxometry. Both the solid effect and Overhauser DNP were observed for the asphaltene solution in benzene, as well as in the solution and solid states for synthetic compounds. By comparison with a solution of synthetic vanadyl porphyrins, it is shown that vanadyl porphyrins in asphaltene aggregates are localized outside of the interface of the asphaltene aggregates and more exposed to the maltene molecules than "free"carbon-centered radicals associated with the core of asphaltene molecules. The perceptible contribution of scalar interaction is observed in solutions for both synthetic and asphaltene vanadyl porphyrins

Raman spectroscopy as a tool to evaluate oxygen effects on the response of polymer gel dosimetry

Se seleccionó la licencia Creative Commons para este envío. El documento trae lo siguiente: CC BY-NC-ND. (En caso de duda consultar a Meilyn Garro).Currently, advanced dosimeters like polymer gels are capable of obtaining reliable and accurate 3D dose distributions from correlations with the different polymerization degrees induced by incident radiation. Samples of polymer gel dosimeters are commonly read out using magnetic resonance imaging or optical methods like visible light transmission or laser computed tomography. Alternatively, this work proposes and evaluates the implementation of Raman spectroscopy to provide direct information on the effect of oxygen permeating through the walls of phantoms on the polymerization initiated by irradiation in three types of polymer gel dosimeters, namely NIPAM, ITABIS and PAGAT. The aim of the present study is to provide better and complete interpretations using three different containers, adequate for integral, 2D and 3D dose mapping. Moreover, Raman spectroscopy has been used to analyze the well-known effect of oxygen inhibition on the different polymer gel dosimeters remarking the importance of avoiding air exposition during sample storage and readout. Dose-response curves for different polymer gels were obtained in terms of measurements with a calibrated ionization chamber. Additionally, dedicated Monte Carlo simulations were performed aimed at characterizing dose for different X-ray irradiation setups, providing also suitable information to evaluate oxygen diffusion through the sample wall. The obtained results were contrasted with optical transmission readout as well as Monte Carlo simulations attaining very good agreements for all dosimeter types. © 2019 Elsevier LtdActualmente, los dosímetros avanzados como los geles poliméricos son capaces de obtener distribuciones de dosis 3D fiables y precisas a partir de correlaciones con los diferentes grados de polimerización inducidos por la radiación incidente. Las muestras de dosímetros de gel de polímero se leen comúnmente utilizando imágenes por resonancia magnética o métodos ópticos como la transmisión de luz visible o la tomografía computarizada con láser. Alternativamente, este trabajo propone y evalúa la implementación de la espectroscopía Raman para proporcionar información directa sobre el efecto del oxígeno que penetra a través de las paredes de los maniquíes sobre la polimerización iniciada por irradiación en tres tipos de dosímetros de gel de polímero, a saber, NIPAM, ITABIS y PAGAT. El objetivo del presente estudio es proporcionar interpretaciones mejores y completas utilizando tres contenedores diferentes, adecuados para mapeo de dosis integral, 2D y 3D. Además, se ha utilizado la espectroscopia Raman para analizar el conocido efecto de la inhibición del oxígeno en los diferentes dosímetros de gel polimérico, destacando la importancia de evitar la exposición al aire durante el almacenamiento y la lectura de la muestra. Se obtuvieron curvas de dosis-respuesta para diferentes geles de polímero en términos de mediciones con una cámara de ionización calibrada. Además, se realizaron simulaciones específicas de Monte Carlo destinadas a caracterizar la dosis para diferentes configuraciones de irradiación de rayos X, proporcionando también información adecuada para evaluar la difusión de oxígeno a través de la pared de la muestra. Los resultados obtenidos se contrastaron con lectura de transmisión óptica y simulaciones de Monte Carlo logrando muy buenas concordancias para todos los tipos de dosímetros. © 2019 Elsevier LtdLaboratorio de Investigación e Instrumentación en Física Aplicada a la Medicina e Imágenes por Rayos X (LIIFAMIRx)Universidad Nacional de Córdoba, M. Allende s/n, Córdoba, ArgentinaDepartamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, CONICET, CórdobaInstituto de Física Enrique Gaviola (IFEG) - CONICET, M. Allende s/n, Córdoba, ArgentinaUniversidad Nacional, Costa RicaDepartamento de Físic