Trajectory Extending Kinetic Monte Carlo Simulations to Evaluate Pure and Gas Mixture Diffusivities through a Dense Polymeric Membrane

With renewed interest in CO2 separations, carbon molecular sieving (CMS) membrane performance evaluation requires diffusion coefficients as inputs to have reliable estimate of the permeability. An optimal material is desired to have both high selectivity and permeability. Gases diffusing through dense, CMS and polymeric membranes experience extended sub-diffusive regimes which hinders reliable extraction of diffusion coefficients from mean squared displacement data. We improve the sampling of the diffusive landscape by implementing the trajectory extending kinetic Monte Carlo (TEKMC) technique to efficiently extend MD trajectories from ns to {\mu}s timescales. The obtained self-diffusion coefficient of pure CO2 in CMS membranes derived from 6FDA/BPDA-DAM precursor polymer melt is found in agreement with previous experimental findings. We also extend the TEKMC algorithm to evaluate the mixture diffusivities in binary mixtures to determine the permselectivity of CO2 in CH4 and N2 mixtures. The mixture diffusion coefficient of CO2 ranges from 1.3-7 x 10^{-6} cm6{2}s^{-1} in binary mixture CO2:CH4 which is significantly higher than the pure gas diffusion coefficient. Robeson plot comparisons show that the permselectivity obtained from pure gas diffusion data are significantly lower than that predicted using mixture diffusivity data. Specifically in the case of the CO2:N2 mixture we find that using mixture diffusivities led to permeslectivites lying above the Robeson limit highlighting the importance of using mixture diffusivity data for an accurate evaluation of the membrane performance. Combined with gas solubilities obtained from grand-canonical Monte Carlo simulations, our work shows that simulations with the TEKMC method can be used to reliably evaluate the performance of materials for gas separations.Comment: Software available on https://github.com/PKMLab/tekmc Accepted on October 25, 2023 in The Journal of Physical Chemistry

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO2 and CH4 to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH2, H2PO3, NO2, and CH3. Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO2 to exceed that of CH4 by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH2, H2PO3, NO2, and COOH functional groups can significantly enhance gas binding with respect to a hydrogen-passivated edge, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO2/CH4 selectivity are discussed.Comment: 12 pages, 7 figure

Audiodescripción de referentes culturales: estudio descriptivo-comparativo y de recepción

La audiodescripción (AD) entendida como un servicio de apoyo a la comunicación con personas ciegas o con baja visión está adquiriendo cada vez más importancia profesional, social y académica. Las cifras actuales de programas que se ofrecen con AD en la televisión española, los congresos y seminarios sobre AD que se celebran en todo el mundo y el avance legislativo en materia de accesibilidad dan buena cuenta de ello. La accesibilidad reivindica su lugar en los Estudios sobre Traducción (y más concretamente, sobre Traducción Audiovisual) y aunque el interés investigador es bastante reciente, sobre todo en España, también es prolífica y ha abordado con profundidad numerosos aspectos específicos tanto del contenido conceptual como de la forma lingüística de la práctica audiodescriptora. La gran mayoría de los trabajos publicados han sido, hasta hace poco, de corte descriptivista. Y aunque indispensables, actualmente es necesario llevar a cabo estudios que corroboren o, al contrario, desestimen las conclusiones a las que se han llegado en dichos estudios descriptivos (Braun, 2008: 22-23). Los estudios de recepción están destinados a ocupar un lugar privilegiado en la investigación en Traducción Audiovisual, y muy concretamente en la investigación sobre accesibilidad, puesto que son los destinatarios de la audiodescripción o de la subtitulación para sordos, por ejemplo, los que han de expresarse y decir (e incluso exigir) cómo deberían ser los productos audiovisuales que les están dirigidos a ellos. Los estudios sobre AD alternativas, no convencionales (Fryer y Freeman, 2012 y 2013; Udo y Fels, 2009a y 2009b; Udo, Acevedo y Fels, 2010) cobran especial importancia para esta tesis, ya que se adentran directamente en la investigación de preferencias y expectativas de los usuarios, algo en lo que pretendemos dar nuestros primeros pasos. Los estudios de recepción sobre preferencias y expectativas del colectivo de personas ciegas o con baja visión son escasos en España, ya que los realizados hasta este momento se centran esencialmente en la evaluación de distintos aspectos de la comprensión o impacto emocional. Esta tesis presenta dos estudios distintos pero complementarios que confluyen en la consecución de un único objetivo: promover la visibilidad del colectivo de personas ciegas o con baja visión, de sus necesidades y expectativas en materia de accesibilidad audiovisual. Para ello, pretendemos demostrar que la ubicación geográfica, cultural y lingüística de los agentes intervinientes en la AD, condicionan, si no determinan, el resultado de esta, entendida como proceso y como producto; y que las decisiones del descriptor se adecuan a las expectativas de sus receptores meta. Para ello, y con carácter previo, se determinan tres objetivos preliminares que suponen la base teórica y práctica necesaria para abordar el estudio experimental que conforma el núcleo duro de la presente tesis. Perseguimos, en un primer momento, describir el panorama actual de la audiodescripción en España, revisar la literatura académica que hasta hoy se ha publicado sobre audiodescripción y establecer un perfil del receptor medio de la audiodescripción en España. A continuación, la presente tesis se articula en dos partes fundamentales y complementarias. Cada estudio persigue un objetivo principal. Por una parte, la finalidad del estudio descriptivo es analizar y evaluar el elemento cultural presente en la audiodescripción de películas en dos lenguas y para dos audiencias meta distintas. Para ello se identifican, analizan, comparan y describen las técnicas de traducción empleadas para describir referentes culturales. Por otra parte, el objetivo del estudio de recepción o experimental consiste en determinar si las AD que se realizan en la actualidad en España se adecuan a las preferencias y expectativas de los usuarios y, en su caso, proponer directrices o recomendaciones para la audiodescripción de referentes culturales en España

In-home evaluation of efficacy and titration of a mandibular advancement device for obstructive sleep apnea

There is increasing evidence that mandibular advancement devices (MADs) can be an effective treatment for some patients with obstructive sleep apnea, a highly prevalent chronic disease. In this study, the objectives were to objectively assess the effectiveness of MAD therapy using a limited channel recorder, and to develop a model for identifying patients who may be appropriate for MAD therapy as the initial treatment option. Thirty patients were prospectively recruited and studied at two independent dentist offices and the participants’ homes. Subjects wore the ARES Unicorder for two nights before insertion of the MAD, and again when the dentist determined that the patient had reached the titration endpoint. Self-reported measures of depression, sleepiness, and quality of life were obtained pre- and posttreatment. The reviewer was blinded to the study status while the physiological signals were being visually inspected. Significant reductions in the apnea/hypopnea index (AHI), hypoxemia measures, and snoring level were observed posttreatment. Twenty-seven of the 30 (90%) patients had a posttreatment AHI (using a 4% desaturation for hypopneas) below a clinical cut-off of 10. All but one patient (97%) exhibited at least a 50% decrease in AHI or had a posttreatment AHI ≤ 10. Significant differences in body mass index, weight, and neck circumference in patients with posttreatment AHIs above and below a clinical cut-off of five were identified. The linear regression used to predict the posttreatment AHI using pretreatment data resulted in an R2 of 0.68. The model correctly predicted two patients who were unable to obtain a posttreatment AHI of 10 or less. This study was designed to demonstrate two models of collaboration between a dental sleep medicine specialist and a sleep medicine physician in the monitoring of a patient treated with a MAD. The outcome data suggest that the limited channel recording system can be used as an alternative to laboratory polysomnography to reduce the cost of MAD treatment, and to improve the quality and consistency of posttreatment patient care

Reduced Slow-Wave Sleep Is Associated with High Cerebrospinal Fluid A beta 42 Levels in Cognitively Normal Elderly

Study Objectives: Emerging evidence suggests a role for sleep in contributing to the progression of Alzheimer disease (AD). Slow wave sleep (SWS) is the stage during which synaptic activity is minimal and clearance of neuronal metabolites is high, making it an ideal state to regulate levels of amyloid beta (Aβ). We thus aimed to examine relationships between concentrations of Aβ42 in the cerebrospinal fluid (CSF) and measures of SWS in cognitively normal elderly subjects. Methods: Thirty-six subjects underwent a clinical and cognitive assessment, a structural MRI, a morning to early afternoon lumbar puncture, and nocturnal polysomnography. Correlations and linear regression analyses were used to assess for associations between CSF Aβ42 levels and measures of SWS controlling for potential confounders. Resulting models were compared to each other using ordinary least squared linear regression analysis. Additionally, the participant sample was dichotomized into “high” and “low” Aβ42 groups to compare SWS bout length using survival analyses. Results: A significant inverse correlation was found between CSF Aβ42 levels, SWS duration and other SWS characteristics. Collectively, total SWA in the frontal lead was the best predictor of reduced CSF Aβ42 levels when controlling for age and ApoE status. Total sleep time, time spent in NREM1, NREM2, or REM sleep were not correlated with CSF Aβ42. Conclusions: In cognitively normal elderly, reduced and fragmented SWS is associated with increases in CSF Aβ42, suggesting that disturbed sleep might drive an increase in soluble brain Aβ levels prior to amyloid deposition

Orexin-A is Associated with Increases in Cerebrospinal Fluid Phosphorylated-Tau in Cognitively Normal Elderly Subjects

Study Objectives: To evaluate the role of orexin-A with respect to cerebrospinal fluid (CSF) Alzheimer disease (AD) biomarkers, and explore its relationship to cognition and sleep characteristics in a group of cognitively normal elderly individuals. Methods: Subjects were recruited from multiple community sources for National Institutes of Health supported studies on normal aging, sleep and CSF biomarkers. Sixty-three participants underwent home monitoring for sleep-disordered breathing, clinical, sleep and cognitive evaluations, as well as a lumbar puncture to obtain CSF. Individuals with medical history or with magnetic resonance imaging evidence of disorders that may affect brain structure or function were excluded. Correlation and linear regression analyses were used to assess the relationship between orexin-A and CSF AD-biomarkers controlling for potential sociodemographic and sleep confounders. Results: Levels of orexin-A, amyloid beta 42 (Aβ42), phosphorylated-tau (P-Tau), total-tau (T-Tau), Apolipoprotein E4 status, age, years of education, reported total sleep time, number of awakenings, apnea-hypopnea indices (AHI), excessive daytime sleepiness, and a cognitive battery were analyzed. Subjects were 69.59 ± 8.55 years of age, 57.1% were female, and 30.2% were apolipoprotein E4+. Orexin-A was positively correlated with Aβ42, P-Tau, and T-Tau. The associations between orexin-A and the AD-biomarkers were driven mainly by the relationship between orexin-A and P-Tau and were not influenced by other clinical or sleep characteristics that were available. Conclusions: Orexin-A is associated with increased P-Tau in normal elderly individuals. Increases in orexin-A and P-Tau might be a consequence of the reduction in the proportion of the deeper, more restorative slow wave sleep and rapid eye movement sleep reported with aging. Clinical Trial Registration: Clinicaltrials.gov registration number NCT01962779. Significance Orexin is a key regulator of sleep-wake homeostasis. Deposition of abnormal phosphorylated tau (P-Tau) in neurons and glia is one of the major features of Alzheimer's disease (AD). Our results show a positive association between cerebrospinal fluid (CSF) levels of orexin-A and P-Tau in a group of cognitively normal elderly. Further, this correlation was not influenced by total sleep time, number of awakenings or sleep disordered breathing. Both findings could be explained by the decrease in the proportion of deeper restorative sleep stages that is part of normal aging or, alternatively, by AD pathology causing orexin dysfunction early in the disease process. Understanding the role of orexin dysfunction in older adults might help unfold new preventive therapies for AD