Influence of Average Free Volume Element Size on the Transport of Gases Through Polymers With Equivalent Total Free Volumes

2002 ◽  
Vol 752 ◽  
Author(s):  
Broderick R. Wilks ◽  
Won J. Chung ◽  
Peter J. Ludovice ◽  
Mary E. Rezac ◽  
Pavla Meakin ◽  
...  
Keyword(s):  
Free Volume ◽  
Defect Size ◽  
Volume Element ◽  
Model Systems ◽  
Average Lifetime ◽  
Fractional Free Volume ◽  
Element Size ◽  
Depth Analysis ◽  
Average Defect ◽  
The Impact

ABSTRACTThe permeability coefficients of gases through glassy polymers have been correlated with the fractional free volume (FFV) of the polymers. In general, polymers with high fractional free volumes have high permeabilities while those with low FFV have low permeabilities. This observation is valid for many, but not all materials. This study evaluates the impact of the average size of a free volume element on the permeability of gases through the polymer.Evaluation of the influence of average free volume element size is only possible by employing model systems in which the chemistry and the total free volume are essentially equivalent. In this study, two stereochemical forms of a methyl-substituted polynorbornene were employed. The isomers are chemically equivalent, with similar total free volumes (0.181 versus 0.188). The average defect size was probed using positron annihilation lifetime spectroscopy. The ortho-positronium lifetimes were measured and it was determined that the difference between the two isomers was approximately 10% with the lower-FFV isomer having the larger average lifetime. For simplicity, the two isomers will be termed Pd and Ni (in reference to the catalysts used in their preparation). The Pd isomer has a slightly lower FFV, but larger average defect size. The Ni isomer has a higher FFV, but smaller average defect size.Transport evaluation indicates that the Pd-isomer has gas permeabilities two to three times those of the Ni-isomer. In depth analysis indicates that the increase in permeability is a result of an increase in both the diffusivity of gases through the polymer and gas solubility.

Impact of average free-volume element size on transport in stereoisomers of polynorbornene. I. Properties at 35 °C

2003 ◽  
Vol 41 (18) ◽  
pp. 2185-2199 ◽  
Author(s):  
Broderick R. Wilks ◽  
Won J. Chung ◽  
Peter J. Ludovice ◽  
Mary R. Rezac ◽  
Pavla Meakin ◽  
...  
Keyword(s):  
Free Volume ◽  
Volume Element ◽  
Element Size

scholarly journals Amorphous polymer dynamics and free volume element size distributions from ultrafast IR spectroscopy

2020 ◽  
Vol 117 (25) ◽  
pp. 13949-13958 ◽  
Author(s):  
David J. Hoffman ◽  
Sebastian M. Fica-Contreras ◽  
Michael D. Fayer
Keyword(s):  
Probability Distribution ◽  
Free Volume ◽  
Stark Effect ◽  
Dynamic Properties ◽  
Amorphous Polymer ◽  
Polymeric Materials ◽  
Volume Element ◽  
Probe Molecule ◽  
Pump Probe ◽  
Element Size

A method for measuring the size and size probability distribution of free volume regions in polymeric materials using ultrafast infrared (IR) polarization-selective pump–probe experiments is presented. Measurements of the ultrafast dynamics of a vibrational probe (the CN stretch of phenyl selenocyanate) in poly(methyl methacrylate) show that the probe dynamics are highly confined. The degree of confinement was found to be both time-dependent and dependent on the vibrational frequency of the probe molecule. The experiments demonstrate that different vibrational frequencies correspond to distinct subensembles of probe molecules that have different dynamic properties determined by their local structural environments. By combining the degree of dynamical confinement with the molecular size of the probe molecule, the free volume element size probability distribution was determined and found to be in good agreement with the best established experimental measure of free volume. The relative probability of a free volume element size is determined by the amplitude of the nitrile absorption spectrum at the frequency of the measurement. The inhomogeneous broadening of the spectrum was linked to the vibrational Stark effect, which permits site selectivity. The observed dynamics at each frequency were then associated with a different size free volume element and distinct local electric field. The multiple timescales observed in the pump–probe experiments were connected to local structural fluctuations of the free volume elements.

scholarly journals Light-curing effects in acrylic-type dental nanocomposites probed by annihilating positrons: the case of loosely monolith Dipol® restoratives

2020 ◽  
Vol 10 (12) ◽  
pp. 4753-4758
Author(s):  
Olha Shpotyuk ◽  
Adam Ingram ◽  
Oleh Shpotyuk ◽  
Jozef Cebulski ◽  
Nina Smolar
Keyword(s):  
Free Volume ◽  
Polymer Matrix ◽  
Light Exposure ◽  
Average Lifetime ◽  
Annihilation Process ◽  
Fractional Free Volume ◽  
Positron Annihilation Lifetime ◽  
Light Curing ◽  
Semi Empirical ◽  
Dental Restorative

AbstractThe possibility of application of positron annihilation lifetime (PAL) spectroscopy to commercially available dimethacrylate-based dental restorative composites Dipol® (Oksomat-AN Ltd, Ukraine) subjected to photopolymerization due to light curing is analyzed. The governing annihilation process in these composites is identified as mixed positron (e+)-positronium (Ps) trapping, where Ps decaying is caused entirely by input from free-volume holes in polymer matrix superimposed on free e+-trapping contribution from interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Photopolymerization shrinkage is revealed through decrease in the average lifetime of annihilating positrons due to opposite changes in Ps-decaying and e+-trapping channels. The growing light-activated polymerization is characteristic of both intensities related to the second and third components in the unconstrained ×3-term decomposed PAL spectra, accompanied by decrease in the corresponding lifetimes. This process resulted in enhanced trapping rate in the defects and depressed fractional free-volume saturation with light curing. Light exposure causes smaller voids in composites owing to free-volume fragmentation in Ps- and e+-trapping sites. The microstructure scenario for these transformations includes photo-induced cross-linking of structural chains in the polymer matrix, followed by conversion of o-Ps traps in interfacial free-volume voids near agglomerated filler nanoparticles. A meaningful description of this process is developed on the basis of the semi-empirical model exploring the  ×3– ×2-coupling decomposition algorithm.

The Catholic Diaspora—Experiences of Evacuation

2018 ◽  
Author(s):  
Thomas Brodie
Keyword(s):  
Urban Areas ◽  
Religious Practice ◽  
Catholic Clergy ◽  
Profound Influence ◽  
The Social ◽  
Depth Analysis ◽  
Nazi Era ◽  
Mass Evacuation ◽  
The Impact ◽  
Pastoral Practice

This chapter analyses the impact exerted on the Catholic Church’s pastoral networks in Germany by the mass evacuation of laypeople from bombed urban areas as of 1941. Drawing on the voluminous correspondence of priests and curates despatched from the Rhineland and Westphalia to Saxony, Thuringia, Silesia, Austria, and elsewhere to minister to Catholic evacuees, this chapter provides in-depth analysis of the social and cultural histories of religious practice in wartime Germany. It demonstrates that the evacuation of laypeople—a topic long neglected within histories of wartime religious practice—exerted a profound influence on pastoral practice by the years 1943–5, placing unprecedented pressures on the Catholic clergy of the dioceses central to this study (Aachen, Cologne and Münster). This chapter therefore also casts new light on regionalism in Germany during the Nazi era.

scholarly journals Decreased Medical Care During the COVID-19 Pandemic – A Comprehensive Analysis of Radiological Examinations

2021 ◽  
Author(s):  
Annette Aigner ◽  
Bernd Hamm ◽  
Florian Nima Fleckenstein ◽  
Tazio Maleitzke ◽  
Georg Böning ◽  
...  
Keyword(s):  
Medical Care ◽  
Control Period ◽  
Surrogate Marker ◽  
Medical Specialty ◽  
Case Volume ◽  
Medical Specialties ◽  
Key Points ◽  
Depth Analysis ◽  
The Impact ◽  
Radiological Examinations

Objectives As a cross-section discipline within the hospital infrastructure, radiological departments might be able to provide important information regarding the impact of the COVID-19 pandemic on healthcare. The goal of this study was to quantify changes in medical care during the first wave of the pandemic using radiological examinations as a comprehensive surrogate marker and to determine potential future workload. Methods A retrospective analysis of all radiological examinations during the first wave of the pandemic was performed. The number of examinations was compared to time-matched control periods. Furthermore, an in-depth analysis of radiological examinations attributed to various medical specialties was conducted and postponed examinations were extrapolated to calculate additional workload in the near future. Results A total of 596,760 examinations were analyzed. Overall case volumes decreased by an average of 41 % during the shutdown compared to the control period. The most affected radiological modalities were sonography (–54 %), X-ray (–47 %) followed by MRI (–42 %). The most affected medical specialty was trauma and orthopedics (–60 % case volume) followed by general surgery (–49 %). Examination numbers increased during the post-shutdown period leading to a predicted additional workload of up to 22 %. Conclusion This study shows a marked decrease in radiological examinations in total and among several core medical specialties, indicating a significant reduction in medical care during the first COVID-19 shutdown. Key Points: Citation Format

scholarly journals Ontogenetic shift in the trophic role of the invasive killer shrimp Dikerogammarus villosus: a stable isotope study

2021 ◽  
Author(s):  
Francesco Mancini ◽  
Raffaele De Giorgi ◽  
Alessandro Ludovisi ◽  
Salvatrice Vizzini ◽  
Giorgio Mancinelli
Keyword(s):  
Dietary Habits ◽  
Trophic Position ◽  
Ecological Impact ◽  
Central Italy ◽  
Local Conditions ◽  
Dikerogammarus Villosus ◽  
Isotopic Signatures ◽  
Depth Analysis ◽  
Stable Isotope Study ◽  
The Impact

AbstractThe introduction of the amphipod Dikerogammarus villosus in European fresh waters is to date recognized as a threat to the integrity of invaded communities. Predation by D. villosus on native benthic invertebrates is assumed as the key determinant of its ecological impact, yet available information describe the species as a primary consumer as well as a carnivore depending on local conditions. Here, we assessed the trophic position (TP) of D. villosus in Lake Trasimeno, a recently invaded lentic system in central Italy, using the CN isotopic signatures of individuals captured in winter spanning two orders of magnitude in body size. TP estimations were compared with those characterizing the native amphipod Echinogammarus veneris and other representative invertebrate predators. On average, D. villosus showed a trophic position higher than E. veneris, and comparable with that of odonate nymphs. An in-depth analysis revealed that large-sized individuals had a trophic position of 3.07, higher than odonates and close to that of the hirudinean predator Erpobdella octoculata, while small-sized specimens had a trophic position of 2.57, similar to that of E. veneris (2.41). These findings indicate that size-related ontogenetic shifts in dietary habits may per se vary the nature of the interaction between Dikerogammarus villosus and native invertebrates from competition to predation. Information collated from published isotopic studies corroborated the generality of our results. We conclude that intra-specific trophic flexibility may potentially amplify and make more multifaceted the impact of the species on other invertebrate species in invaded food webs.

scholarly journals Corporate Social Responsibility Disclosure: Responding to Investors’ Criticism on Social Media

2021 ◽  
Vol 18 (14) ◽  
pp. 7396
Author(s):  
Yuming Zhang ◽  
Fan Yang
Keyword(s):  
Social Media ◽  
Corporate Social Responsibility ◽  
Social Responsibility ◽  
Social Issues ◽  
Media Criticism ◽  
Csr Communication ◽  
Depth Analysis ◽  
Csr Disclosure ◽  
Corporate Social ◽  
The Impact

Companies use corporate social responsibility (CSR) disclosures to communicate their social and environmental policies, practices, and performance to stakeholders. Although the determinants and outcomes of CSR activities are well understood, we know little about how companies use CSR communication to manage a crisis. The few relevant CSR studies have focused on the pressure on corporations exerted by governments, customers, the media, or the public. Although investors have a significant influence on firm value, this stakeholder group has been neglected in research on CSR disclosure. Grounded in legitimacy theory and agency theory, this study uses a sample of Chinese public companies listed on the Shanghai Stock Exchange to investigate CSR disclosure in response to social media criticism posted by investors. The empirical findings show that investors’ social media criticism not only motivates companies to disclose their CSR activities but also increases the substantiveness of their CSR reports, demonstrating that companies’ CSR communication in response to a crisis is substantive rather than merely symbolic. We also find that the impact of social media criticism on CSR disclosure is heterogeneous. Non-state-owned enterprises, companies in regions with high levels of environmental regulations, and companies in regions with local government concern about social issues are most likely to disclose CSR information and report substantive CSR activities. We provide an in-depth analysis of corporate CSR strategies for crisis management and show that crises initiated by investors on social media provide opportunities for corporations to improve their CSR engagement.

scholarly journals Gut-Ex-Vivo system as a model to study gluten response in celiac disease

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Mara Gagliardi ◽  
Nausicaa Clemente ◽  
Romina Monzani ◽  
Luca Fusaro ◽  
Eleonora Ferrari ◽  
...  
Keyword(s):  
Celiac Disease ◽  
Intestinal Epithelium ◽  
Complex Disease ◽  
Ex Vivo ◽  
Dynamic Condition ◽  
Model Systems ◽  
In Vivo Models ◽  
Effective Manner ◽  
Junction Protein ◽  
The Impact

AbstractCeliac disease (CD) is a complex immune-mediated chronic disease characterized by a consistent inflammation of the gastrointestinal tract induced by gluten intake in genetically predisposed individuals. Although initiated by the interaction between digestion-derived gliadin, a gluten component, peptides, and the intestinal epithelium, the disorder is highly complex and involving other components of the intestine, such as the immune system. Therefore, conventional model systems, mainly based on two- or three-dimension cell cultures and co-cultures, cannot fully recapitulate such a complex disease. The development of mouse models has facilitated the study of different interacting cell types involved in the disorder, together with the impact of environmental factors. However, such in vivo models are often expensive and time consuming. Here we propose an organ ex vivo culture (gut-ex-vivo system) based on small intestines from gluten-sensitive mice cultivated in a dynamic condition, able to fully recapitulate the biochemical and morphological features of the mouse model exposed to gliadin (4 weeks), in 16 h. Indeed, upon gliadin exposure, we observed: i) a down-regulation of cystic fibrosis transmembrane regulator (CFTR) and an up-regulation of transglutaminase 2 (TG2) at both mRNA and protein levels; ii) increased intestinal permeability associated with deregulated tight junction protein expression; iii) induction and production of pro-inflammatory cytokines such as interleukin (IL)-15, IL-17 and interferon gamma (IFNγ); and iv) consistent alteration of intestinal epithelium/villi morphology. Altogether, these data indicate that the proposed model can be efficiently used to study the pathogenesis of CD, test new or repurposed molecules to accelerate the search for new treatments, and to study the impact of the microbiome and derived metabolites, in a time- and cost- effective manner.

scholarly journals Synchronization in 5G networks: a hybrid Bayesian approach toward clock offset/skew estimation and its impact on localization

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Meysam Goodarzi ◽  
Darko Cvetkovski ◽  
Nebojsa Maletic ◽  
Jesús Gutiérrez ◽  
Eckhard Grass
Keyword(s):  
Bayesian Approach ◽  
Large Scale ◽  
Hybrid Approach ◽  
Position Estimation ◽  
5G Networks ◽  
Clock Skew ◽  
Depth Analysis ◽  
The Impact ◽  
Mean Square Errors ◽  
Clock Offset

AbstractClock synchronization has always been a major challenge when designing wireless networks. This work focuses on tackling the time synchronization problem in 5G networks by adopting a hybrid Bayesian approach for clock offset and skew estimation. Furthermore, we provide an in-depth analysis of the impact of the proposed approach on a synchronization-sensitive service, i.e., localization. Specifically, we expose the substantial benefit of belief propagation (BP) running on factor graphs (FGs) in achieving precise network-wide synchronization. Moreover, we take advantage of Bayesian recursive filtering (BRF) to mitigate the time-stamping error in pairwise synchronization. Finally, we reveal the merit of hybrid synchronization by dividing a large-scale network into local synchronization domains and applying the most suitable synchronization algorithm (BP- or BRF-based) on each domain. The performance of the hybrid approach is then evaluated in terms of the root mean square errors (RMSEs) of the clock offset, clock skew, and the position estimation. According to the simulations, in spite of the simplifications in the hybrid approach, RMSEs of clock offset, clock skew, and position estimation remain below 10 ns, 1 ppm, and 1.5 m, respectively.

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