Search Results (10)

This work aims to determine the mechanism of the photomechanical response of poly(Methyl methacrylate) polymer doped with the photo-isomerizable dye Disperse Red 1 using the non-isomerizable dye Disperse Orange 11 as a control to isolate photoisomerization. Samples are free-standing thin films with thickness that is small compared with the optical skin depth to assure uniform illumination and photomechanical response throughout their volume, which differentiates these studies from most others. Polarization-dependent measurements of the photomechanical stress response are used to deconvolute the contributions of angular hole burning, molecular reorientation and photothermal heating. While photo-isomerization of dopant molecules is commonly observed in dye-doped polymers, the shape changes of a molecule might not couple strongly to the host polymer through steric mechanical interactions, thus not contributing substantially to a macroscopic shape change. To gain insights into the effectiveness of such mechanical coupling, we directly probe the dopant molecules using dichroism measurements simultaneously while measuring the photomechanical response and find mechanical coupling to be small enough to make photothermal heating—mediated by the transfer of optical energy as heat to the polymer—the dominant mechanism. We also predict the fraction of light energy converted to mechanical energy using a model whose parameters are thermodynamic material properties that are measured with independent experiments. We find that in the thin-film geometry, these dye-doped glassy polymers are as efficient as any other material but their large Young’s modulus relative to other organic materials, such as liquid crystal elastomers, makes them suitable in applications that require mechanically strong materials. The mechanical properties and the photomechanical response of thin films are observed to be significantly different than in fibers, suggesting that the geometry of the material and surface effects might play an important role. Full article

The aim of this work is to investigate the influence of the ethanol content of adducts on the catalytic behavior of related Ziegler–Natta (ZN) catalysts in propylene homo- and copolymerizations (with 1-hexene comonomer) in terms of activity, isotacticity, H₂ response, and comonomer incorporation. For this purpose, three MgCl₂.nEtOH adducts with n values of 0.7, 1.2, and 2.8 were synthesized and used in the synthesis of related ZN catalysts. The catalysts were thoroughly characterized using XRD, BET, SEM, EDX, N₂ adsorption–desorption, and DFT techniques. Additionally, the microstructure of the synthesized (co)polymers was distinguished via DSC, SSA, and TREF techniques. Their activity was found to enhance with the adduct’s ethanol content in both homo- and copolymerization experiments, and the increase was more pronounced in homopolymerization reactions in the absence of H₂. Furthermore, the catalyst with the highest ethanol content provided a copolymer with a lower isotacticity index, a shorter meso sequence length, and a more uniform distribution of comonomer within the chains. These results were attributed to the higher total surface area and Ti content of the corresponding catalyst, as well as its lower average pore diameter, a larger proportion of large pores compared to the other two catalysts, and its spherical open bud morphology. It affirms the importance of catalyst/support ethanol-content control during the preparation process. Then, molecular simulation was employed to shed light on the iso-specificity of the polypropylene produced via synthesized catalysts. Full article

This work studies the effect of azobenzene dye Disperse Red 1 (DR1) doping and annealing on the thermomechanical and photomechanical properties of poly(methyl methacrylate) (PMMA) fibers. The mechanical properties are measured as a function of temperature, pump light intensity, and polarization. We find that doping with DR1 increases the stiffness and the glass transition temperature ($T_g$) of the PMMA fibers. Moreover, annealing below $T_g$ decreases Young’s modulus and increases $T_g$. Finally, the photothermal heating contribution to the photomechanical response and the length change during laser exposure are determined in both unannealed and annealed plain PMMA and DR1-doped PMMA fibers. We find that photothermal heating is the dominant mechanism and the effect of photoisomerization is negligible. The temperature-dependent photomechanical efficiencies are also determined. Full article

This research studies the traces of an ancestral textile produced in karkhanehs (workspaces) located in the historical city of Yazd, Iran. The case study undertaken here demonstrates how an intangible heritage of textile weaving through generations of families in Yazd, Iran, interrelates with tangible vernacular architecture and tourism at three different scales: (i) in everyday life in karkhanehs at home, (ii) in the neighborhoods, and (iii) the UNESCO World Heritage city of Yazd. The three scales related to the enactment of this vernacular handicraft are examined using architectural methods to examine structures ranging from 90 to 600 years in age. This was complemented by discussions with local weavers and residents, as well as direct observation in domiciles, neighborhoods, and the city. Actor-Network Theory helped to trace the networks of actors and relationships between the tangible built architectural heritage and intangible cultural practices of weaving, showing how different genders, ages, worldviews (beliefs) and practices came together to produce this heritage textile. Actor-Network Theory also helped to study the relationships between economy, culture, society and tourism, with respect to the evolution and transformations of the historic urban dwellings, vernacular architecture and vernacular weaving handicrafts through the three scales examined. Implications for sustaining and conserving this ancestral tradition of textile weaving and managing tourism’s positive as well as disruptive influences on cultural heritage conservation are discussed. Full article

This work is a comprehensive experimental and theoretical study aimed at understanding the photothermal and molecular shape-change contributions to the photomechanical effect of polymers doped with azo dyes. Our prototypical system is the azobenzene dye Disperse Red 1 (DR1) doped into poly (methyl methacrylate) (PMMA) polymer formed into optical fibers. We start by determining the thermo-mechanical properties of the materials with a temperature-dependent stress measurement. The material parameters, so determined, are used in a photothermal heating model—with no adjustable parameters—to predict its contribution. The photothermal heating model predicts the observations, ruling out mechanisms originating in light-induced shape changes of the dopant molecules. The photomechanical tensor response along the two principle axes in the uniaxial approximation is measured and compared with another independent theory of photothermal heating and angular hole burning/reorientation. Again, the results are consistent only with a purely thermal response, showing that effects due to light-induced shape changes of the azo dyes are negligible. The measurements are repeated as a function of polymer chain length and the photomechanical efficiencies determined. We find the results to be mostly chain-length independent. Full article

Background and Objectives: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic condition distinguished by disabling fatigue associated with post-exertional malaise, as well as changes to sleep, autonomic functioning, and cognition. Mind-body interventions (MBIs) utilize the ongoing interaction between the mind and body to improve health and wellbeing. Purpose: To systematically review studies using MBIs for the treatment of ME/CFS symptoms. Materials and Methods: MEDLINE, EMBASE, CINAHL, PsycINFO, and Cochrane CENTRAL were searched (inception to September 2020). Interventional studies on adults diagnosed with ME/CFS, using one of the MBIs in comparison with any placebo, standard of care treatment or waitlist control, and measuring outcomes relevant to the signs and symptoms of ME/CFS and quality of life were assessed for inclusion. Characteristics and findings of the included studies were summarized using a descriptive approach. Results: 12 out of 382 retrieved references were included. Seven studies were randomized controlled trials (RCTs) with one including three reports (1 RCT, 2 single-arms); others were single-arm trials. Interventions included mindfulness-based stress reduction, mindfulness-based cognitive therapy, relaxation, Qigong, cognitive-behavioral stress management, acceptance and commitment therapy and isometric yoga. The outcomes measured most often were fatigue severity, anxiety/depression, and quality of life. Fatigue severity and symptoms of anxiety/depression were improved in nine and eight studies respectively, and three studies found that MBIs improved quality of life. Conclusions: Fatigue severity, anxiety/depression and physical and mental functioning were shown to be improved in patients receiving MBIs. However, small sample sizes, heterogeneous diagnostic criteria, and a high risk of bias may challenge this result. Further research using standardized outcomes would help advance the field. Full article

Mind-body interventions (MBIs) are one of the top ten complementary approaches utilized in pediatrics, but there is limited knowledge on associated adverse events (AE). The objective of this review was to systematically review AEs reported in association with MBIs in children. In this systematic review the electronic databases MEDLINE, Embase, CINAHL, CDSR, and CCRCT were searched from inception to August 2018. We included primary studies on participants ≤ 21 years of age that used an MBI. Experimental studies were assessed for whether AEs were reported on or not, and all other study designs were included only if they reported an AE. A total of 441 were included as primary pediatric MBI studies. Of these, 377 (85.5%) did not explicitly report the presence/absence of AEs or a safety assessment. There were 64 included studies: 43 experimental studies reported that no AE occurred, and 21 studies reported AEs. There were 37 AEs found, of which the most serious were grade 3. Most of the studies reporting AEs did not report on severity (81.0%) or duration of AEs (52.4%). MBIs are popularly used in children; however associated harms are often not reported and lack important information for meaningful assessment. Full article

Epstein-Barr virus (EBV) is associated with a wide range of malignancies and complications like post-transplant lymphoproliferative disorder (PTLD). To suppress active EBV infection in transplant recipients, who are at a heightened risk of developing PTLD, EBV DNAemia monitoring has been recommended. Quantitative multiplex real time polymerase chain reaction (QMRTPCR) offered the advantage of detection of more than one target in the same sample. We present four cases of kidney transplant recipient who were admitted for rising serum creatinine between 9 and 20 months post-transplant with a suspicion of BKV-associated nephropathy. All but one patient had unusual sonography findings in their genitourinary tracts and were positive for urinary culture for bacteria. Using a commercial QMRTPCR that could detect and quantitate BKV, EBV and cytomegalovirus simultaneously, all patients were positive for EBV in their urine for the levels between 2500 and 8×108 U/mL. None of the patients had any symptoms regarding this finding. On following up survey 3 month post discharge from hospital, all patients were negative for plasma and urine EBV. Absent of EBV DNAemia together with alternating phases of detectable EBV in urine might reflect the presence of functionally efficient central/effector memory T cells against EBV. The significance of this finding in immunocompromized patients necessitates prospective longitudinal studies. Full article

Background: Healthcare workers constitute a population at high risk for HBV infection. Efficient vaccination options are available; however, the individual response to HBV vaccination may vary widely between subjects, potentially due to cytokine profiles and genetic variations. In the present study, we investigated the relationship between IL-17 and IL-22 gene polymorphisms versus non- and low-responsiveness to HBV vaccination in healthcare workers. Methods: We selected the following IL-17 and IL-22 polymorphisms: rs4711998 (A/G) from IL-17 and rs2227501 (A/T), rs2227503 (A/G), rs1026786 (A/G) from IL-22 sequences genes. These were determined by polymerase chain reaction restriction fragment length polymorphisms. Results: The IL-17 rs4711998 GG genotype had a significantly lower frequency in non-responders compared to low-responders (p = 0.025). However, we did not identify a relationship between IL-22 rs1026780, rs2227501 and rs2227503 genotypes and the anti-HBs response following HBV vaccination. Conclusion: These data suggest that genetic variation in rs4711998 polymorphisms in the IL-17 cytokine may influence vaccine-induced immune responses to HBV vaccine in healthcare workers. Full article

Background: Worldwide, healthcare workers (HCWs) show different levels of response to hepatitis B virus (HBV) vaccine. One of the factors associated with vaccine unresponsiveness may be the existence of current or past HBV infection. Regardless of the presence of HBsAg (overt infection), occult HBV infection (OBI, defined as presence of HBV DNA in the absence of HBsAg) might also account for some non- or hypo-response cases. Methods: Sera from 120 HBsAg-negative HCWs with low and moderate levels of anti-HBs, <10 IU/mL (group I) and <100 IU/mL (group II) respectively, were selected and were examined for OBI by sensitive real-time PCR regardless of HBV serological profiles. Direct sequencing on surface genes was carried out in OBI-positive cases. Results: Four (3.3%) were positive for OBI. All were negative for anti-HBc. Two of the positive cases had moderate levels of anti-HBs (>10 to <100 IU/mL). No significant differences were found between the two groups in terms of risk factors or serological data. No mutations were found in surface proteins of OBI cases. Conclusion: OBI in these subjects might be due to other factors rather than presence of “a” determinant mutations. Healthcare workers with inadequate to moderate levels of anti-HBs (<100 IU/mL) following vaccination, regardless of their serological profile for HBV, should be tested for the presence of HBV DNA by sensitive molecular tests. Anti-HBc is not a reliable marker for suspicion of OBI, especially in high-risk group individuals. Full article