Chain Transition Research Articles

Coil-Uncoiled Chain Transition of Polyethylene Oxide Solutions under Convergent Flow

Coil-Uncoiled Chain Transition of Polyethylene Oxide Solutions under Convergent Flow

Quantum counterpart of measure synchronization: A study on a pair of Harper systems

Measure synchronization is a well-known phenomenon in coupled classical Hamiltonian systems over last two decades. Here, synchronization in a pair of coupled Harper systems is investigated both in classical and quantum contexts. It seems that the concept of measure synchronization is restricted in the classical limit as it involves with the phase space. We show the quantum counterpart of the synchronization in a pair of coupled quantum kicked Harper chains. In the quantum context, the coupling occurs between two spins chains via a time and site dependent potential. We use the average interaction energy between the participating systems as an order parameter in both the contexts to establish a connection between the classical and the quantum scenarios. Besides, we also study the entanglement between the chains and difference between the average bare energies in the quantum context. Interestingly, all such indicators suggest a connection between the MS transition in classical maps and a phase transition in quantum spin chains.

Phospholipid-induced silk fibroin hydrogels and their potential as cell carriers for tissue regeneration.

Silk fibroin (SF) hydrogels can be obtained via self-assembly, but this process takes several days or weeks, being unfeasible to produce cell carrier hydrogels. In this work, a phospholipid, namely, 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) sodium salt (DMPG), was used to induce and accelerate the gelation process of SF solutions. Due to the amphipathic nature and negative charge of DMPG, electrostatic and hydrophobic interactions between the phospholipids and SF chains will occur, inducing the structural transition of SF chains to the beta sheet and consequently a rapid gel formation is observed (less than 50 min). Moreover, the gelation time can be controlled by varying the lipid concentration. To assess the potential of the hydrogels as cell carriers, several mammalian cell lines, including L929, NIH/3T3, SaOS-2, and CaSki, were encapsulated into the hydrogel. The silk-based hydrogels supported the normal growth of fibroblasts, corroborating their cytocompatibility. Interestingly, an inhibition in the growth of cancer-derived cell lines was observed. Therefore, DMPG-induced SF hydrogels can be successfully used as a 3D platform for in situ cell encapsulation, opening promising opportunities in biomedical applications, such as in cell therapies and tissue regeneration.

Bubble regime identification in an attention-based model for Bitcoin and Ethereum price dynamics

In this paper we extend the model in Cretarola, Figà-Talamanca, “Detecting bubbles in Bitcoin price dynamics via market exuberance”, Annals of Operations Research (2019), by allowing for a state-dependent correlation parameter between asset returns and market attention. We assume that the change of state is described by a continuous time latent Markov chain and we propose an estimation procedure based on the conditional maximum likelihood and on the Hamilton filter. Finally, model parameters, as well as Markov chain transition probabilities, are estimated on Bitcoin and Ethereum returns in case market attention is measured via the Google Search Volume Index for the keywords “bitcoin” and “ethereum”, respectively; up to four regimes are considered in the empirical application. The empirical outcomes show that the model is not only capable of identifying bubble and non-bubble regimes but also enables the interpretation of the correlation between cryptocurrencies and their market attention as a tuning to define the speed at which a bubble boosts.

Quantum criticality in Ising chains with random hyperuniform couplings

We study quantum phase transitions in transverse-field Ising spin chains in which the couplings are random but hyperuniform, in the sense that their large-scale fluctuations are suppressed. We construct a one-parameter family of disorder models in which long-wavelength fluctuations are increasingly suppressed as a parameter $\alpha$ is tuned. For $\alpha = 0$, one recovers the familiar infinite-randomness critical point. For $0 < \alpha < 1$, we find a line of infinite-randomness critical points with continuously varying critical exponents; however, the Griffiths phases that flank the critical point at $\alpha = 0$ are absent at any $\alpha > 0$. When $\alpha > 1$, randomness is a dangerously irrelevant perturbation at the clean Ising critical point, leading to a state we call the critical Ising insulator. In this state, thermodynamics and equilibrium correlation functions behave as in the clean system. However, all finite-energy excitations are localized, thermal transport vanishes, and autocorrelation functions remain finite in the long-time limit. We characterize this line of hyperuniform critical points using a combination of perturbation theory, renormalization-group methods, and exact diagonalization.

Role of Coulomb correlations in the charge density wave of CuTe

A quasi one-dimensional layered material, CuTe undergoes a charge density wave (CDW) transition in Te chains with a modulation vector of $q_{CDW}=(0.4, 0.0, 0.5)$. Despite the clear experimental evidence for the CDW, the theoretical understanding especially the role of the electron-electron correlation in the CDW has not been fully explored. Here, using first principles calculations, we demonstrate the correlation effect of Cu is critical to stabilize the 5$\times$1$\times$2 modulation of Te chains. We find that the phonon calculation with the strong Coulomb correlation exhibits the imaginary phonon frequency so-called phonon soft mode at $q_{ph0}=(0.4, 0.0, 0.5)$ indicating the structural instability. The corresponding lattice distortion of the soft mode agrees well with the experimental modulation. These results demonstrate that the CDW transition in CuTe originates from the interplay of the Coulomb correlation and electron-phonon interaction.

Portfolio-based airline fleet planning under stochastic demand

Airlines operate their fleet of aircraft over a relatively long time horizon during which the realized stochastic demand has the potential to profoundly impact the airlines’ financial performance. This makes the investment in a fleet of aircraft a highly capital-intensive long-term commitment, associated with inherent risks. We propose an innovative three-step airline fleet planning methodology with the primary objective of identifying fleets that are robust to stochastic demand realizations. The methodology presents two main innovation aspects. The first one is the use of the mean reverting Ornstein–Uhlenbeck process to model the long-term travel demand, which is then combined with discrete-time Markov chain transitions to generate demand scenarios. The second innovative aspect is the adoption of a portfolio-based fleet planning perspective that allows for an explicit comparison of different fleets, in size and composition. Ultimately, the methodology yields for each fleet in the portfolio a distribution of net present values of operating profit across the planning horizon and a list of key financial and operational metrics per year. The robustest fleet can be selected based on the operating profit generating capability across different realizations of stochastic demand. An illustrative case study is presented as a proof of concept. The case study is used to demonstrate the type of results obtained and to discuss the usefulness of the methodology proposed.

An effect of ionic liquids on polymorph transformations in polyvinylidenefluoride at its crystallization from solution

According to IR spectroscopy data, crystallization of polyvinylidenefluoride from dimethylformamide and dimethylsulfoxide solutions at 100 °C and 80 °С is accompanied in the last case by the formation of polymorph modification mixtures of γ and β phases. In the presence of a number of ionic liquids, the same crystallization is accompanied by conformation transition in polymer chains from T3GT3G− to the conformation of a planar zigzag. We think that it takes place due to ion-dipole interactions between cations of the imidazole ring with fluorine atoms of polymer chains in the amorphous phase. X-ray data show that polar crystals of the β phase of non-doped polymer contain many conformational defects in the form of T3GT3G− isomers. At polymer doping with ionic liquid, the number of such defects is lowering. Due to this, the density of crystals formed grows. Conformation changes noted affect the signal of electromechanical response fixed by piezoresponse force microscopy. In particular, it has been shown that in the film under conditions of crystallization chosen process of self-polarization, which is registered by the method of Kelvin mode, takes place.

Quantum coherence of the spin-1 system under an XY spin chain with three-spin interaction

We investigate the performance of quantum coherence and nonlocal advantage of quantum coherence (NAQC) for the central spin-1 system which couple to an XY spin chain with three-spin interaction in a transverse magnetic field. For the case that the central spin system couple weakly to the spin chain, both quantum coherence and NAQC endure sudden change around the critical point of quantum phase transitions when the three-spin interaction is switched off. While there is three-spin interaction, the performances of quantum coherence and NAQC indicate that the critical point has been shifted away from its ordinary position. Therefore, quantum coherence and NAQC can be used to detect the critical point of quantum phase transitions of the XY spin chain for the weak-coupling case. However, three-spin interaction has no obvious effect on the dynamics of quantum coherence and NAQC for the strong-coupling case.

Collapse Transition‐Assisted Crystallization in P3HT Solution

ABSTRACTUnderstanding the multiple phase transitions such as collapse transition, phase separation, and crystallization in solutions is of fundamental importance to control the solution structure of conjugated polymers in device processing. Combining in situ synchrotron radiation small and wide‐angle X‐ray scattering, ultrasensitive differential scanning calorimetry, ultraviolet–visible absorption spectroscopy, and polarized optical microscopy, we investigate the order–disorder transitions in poly(3‐hexylthiophene)/toluene solutions during cooling and heating processes. We demonstrate the occurrence of collapse transition of polymer chains from a random coil state to a lower dimensional network prior to the onset of crystallization during cooling in solution. This conformational preordering can lead to the formation of a lyotropic liquid crystalline phase, which is of great significance to the crystallization and ordering in polymer films, and further to promote its electric performance. It is examined that the mobility of films cast from chain‐collapsed solutions can be one order of magnitude higher than that from isotropic solutions with random‐coiled conformations. Thus, the conformational preordering in solutions is proposed to be a more efficient way than the postannealing of films to improve the electric performance of conjugated polymer films. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1105–1114

Morphology and thermodynamics of polymers with monofunctional hydrogen bonding ends in dilute and semidilute concentration.

Rheological properties of supramolecular polymers (SMPs) depend on their equilibrium structure including the size, the number, and the topology of aggregates. A polymer with a hydrogen bonding (H-bonding) motif at both ends is one widely used precursor to build SMPs. Due to the complex interplay between chain stiffness, H-bonding interaction, polarity along a chain, and polymer conformational entropy, it is difficult to theoretically predict the structure of SMPs. In this work we investigate thermodynamics of SMPs with H-bonding ends in a wide range of densities. A replica exchange stochastic approximation Monte Carlo method with coarse-grained models for polyethylene and polybuthylene glycols is used. Our simulation shows that SMPs have two morphological transition lines with increasing temperature, a ring-linear transition, and a linear-free chain transition. The latter is a thermodynamic transition and turns out to be continuous. Comparing the two different spacers, we find that ring-linear transition temperatures differ from each other at the constant volume fraction due to different looping probabilities, which can be calculated from the average polymer size by mean field. However, the linear-free chain transition temperatures are similar because the entropic penalty to form a hydrogen bond mainly depends on the probability of finding H-bonding groups in a system, which is the same for both systems at a given volume fraction.

Controlling the electrostatic interaction using a thermal signal to structurally change thermoresponsive nanoparticles

The negatively charged thermoresponsive polymers poly(benzyl methacrylate)-b-poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PBzMA-b-PAAc-b-PIPAAm) were prepared by reversible-addition fragmentation chain transfer polymerization. The polymer formed core-shell polymeric micelles possessing a thermoresponsive corona composed of PAAc-b-PIPAAm below the lower critical solution temperature (LCST) of the PIPAAm chain. The nonionic thermoresponsive polymeric micelle composed of PBzMA-b-PIPAAm exhibited extensive inter-micellar aggregation after the hydrophobic phase transition of the corona-forming PIPAAm chains. In contrast, insertion of the PAAc chain into the thermoresponsive micelle maintained its dispersibility above the LCST of PIPAAm because of the electrostatic repulsion between the micelles. The micelles with short PAAc chains suppressed the effect of the negative charge derived from PAAc below the LCST because of the extended PIPAAm chain on the micellar surface. In contrast, the negative charge property appeared due to collapse of the PIPAAm layer above the LCST. This thermoresponsive change in its electrostatic behavior enables the micelle to control the adsorption and desorption of oppositely charged molecules in response to the temperature change across the LCST.

Melting Transitions of the Organic Subphase in Layered Two-Dimensional Halide Perovskites.

We investigate the phase behavior of two-dimensional (C xH2 x+1NH3)2[(MA,FA)PbI3] n-1PbI4 layered perovskites near room temperature (-20 °C to +100 °C) as a function of the octahedral layer thickness ( n = 1, 2, 3, 4), alkylammonium chain length (butyl, pentyl, and hexyl), and identity of the small organic cation (methylammonium and formamidinium). Using differential scanning calorimetry and X-ray diffraction, we observe a reversible first-order phase transition corresponding to a partial melting transition of the alkylammonium chains separating the perovskite layers. The melting temperature, Tm, increases from 10 to 77.9 to 95.9 °C as the carbon chain length increases from C4 to C5 to C6, but it is insensitive to octahedral layer thickness, n. The latent heat of melting, Δ Hm, was in the range of 3-5 kJ/mol-spacer, indicating only partial disordering of the carbon chain. We discuss these findings and their implications in the context of melting in other two-dimensional molecular systems.

Silane modified epoxy coatings with low surface tension to achieve self-healing of wide damages

Self-healing behavior of polymer coatings consists of two steps: crack closure and crack repair. Shape-memory effect, conformational transition of polymer chains, and water-induced flowability were reported on crack closure as the preliminary and necessary step. All of them, however, cannot achieve the trade-off between healing from wide damage and satisfied properties. Here, we prepared silane modified epoxy coatings, which achieved the self-healing of cracks with width of 300 μm upon heating and good mechanical properties. Furfurylamine (FA) and furfuryl glycidyl ether (FGE) were reacted with diglycidylether of bisphenol A to prepare oligomers with furan groups as side and terminal groups, which created reversible crosslinking bonds based on Diels-Alder reactions with maleimide groups from bis(4-maleimidophenyl)methane. (3-aminopropyl)triethoxysilane (APTES) was also involved to reduce the surface tension of coatings and to offer irreversible crosslinking bonds that ensured the coating stability during heating. We fully studied the effects of the ratio of APTES and FA (1:9, 2:8, 3:7, and 4:6) on the chemical structures, molecular weight, and thermal properties of oligomers, as well as the chemical structures, surface structures, mechanical properties of coating materials. By increasing the ratio of APTES and FA, the surface tension of the coating was gradually decreased until a critical ratio of 3:7. All coatings possessed similar and good mechanical properties. The self-healing behaviors were found to be dominated by the competition among shape-memory effect, surface tension driven flow, and viscosity, which were related to coating network structures. Thick coatings also facilitated the crack closure and healing performance. Compared with the coating without silane modification, the self-healing behavior was improved, the mechanical properties were maintained, and the anti-corrosion properties were deteriorated.

Global Health Outreach by United States Ophthalmology Residency Programs: Understanding of Host Country Systems-Based Practice.

For medical residents, global health outreach is the first experience of learning how to develop partnerships with foreign medical systems. The overall objective of this project was to develop an overview of global health programs in U.S. ophthalmology residencies. The investigation focused on characterizing the goals and services offered, the didactics taught to residents, and the program director's understanding of systems-based practice gained in the host country. An online survey was sent to all U.S. ophthalmology residency program directors. The two outcome measures of the study were characterization of global health outreach and didactics completed by U.S. ophthalmology residency programs and review of program director understanding of host country systems of care. Twelve program directors of 117 (10.26%) answered the survey. 100% of programs from the Department of Defense responded. Countries served included Ecuador, Panama, Honduras, Dominican Republic, India, Tanzania, Nepal, Bhutan, Guatemala, Micronesia, Haiti, Mongolia, Bolivia. Sixty five percent worked at a free-standing public hospital. Many programs offered resident participation with only 41.87% giving residents ACGME credit. Most programs (91.67%) offered fewer than 5 hours of global health didactics. When program directors were asked about their knowledge of host country systems of care, most noted understanding of the hospital functions like the referral system, transitions of care, hospital funding, and medical supply chain, but not of the perception of patients with chronic or congenital ophthalmic diseases, host country general or ophthalmic medical education, patient research safeguards and host country malpractice system. From the small sample of program directors, Ophthalmology residency program global health outreach varies in faculty and resident participation, and in goals and services offered. In addition, there was a wide variation in ophthalmology program director understanding of host country systems of care.

Phase-transition induced gelation of ZnO suspensions containing thermosensitive poly(acrylic acid)-graft-poly(N-isopropylacrylamide)

Thermosensitive ZnO suspensions containing poly(acrylic acid)-graft-poly(N-isopropylacrylamide) (PAA-g-PNIPAM) are used to prepare complex-shaped ceramic parts by controlling the phase transition of PNIPAM graft chains. The properties of PAA-g-PNIPAM aqueous solution and the rheological behavior of ZnO suspensions with PAA-g-PNIPAM were investigated. The results show that PAA-g-PNIPAM is a pH- and temperature-sensitive polymer, and its lower critical solution temperature is 32 °C. The isoelectric point of ZnO particles shifts from 9.1 to 4.8 after adding PAA-g-PNIPAM, and the adsorption capacity of PAA-g-PNIPAM on ZnO particles decreases with increasing pH value. The 45 vol.% ZnO suspension containing 3.0 mg/g PAA-g-PNIPAM exhibits a good fluidity at room temperature, and a rapid increase in apparent viscosity and shear elastic modulus above 32 °C due to the decay of steric hindrance and the increase of effective volume fraction caused by the phase transition of PNIPAM graft chains. The complex-shaped ceramic parts prepared using thermosensitive ZnO suspensions are in good condition with few pores.

Enhancing oil recovery from low-permeability reservoirs with a self-adaptive polymer: A proof-of-concept study

Considerable success has been achieved in enhanced oil recovery by polymer flooding from high- to medium-permeability reservoirs; however, the poor injectivity and ease of mechanical degradation of the commonly used high-molecular-weight (high-MW) partially hydrolyzed polyacrylamides (HPAM) impede their use in low-permeability reservoirs. To alleviate these issues, we proposed the use of the self-adaptive polymer (SAP). SAP with a relatively low MW (8.7 × 106 g mol−1), a rigid unit, and hydrophobic pendant group was prepared and compared with its counterparts HPAM-1 (8.2 × 106 g mol−1) and HPAM-2 (24.9 × 106 g mol−1). It was found that while the molecular size of SAP is similar to that of HPAM-1, its thickening capability is stronger under identical conditions, and both of them can be smoothly injected into the 60-mDarcy cores. By contrast, HPAM-2 causes fatal plugging in this scenario. The favorable injectivity of SAP solution stems from its reversible viscosity change in response to shear forces without any deterioration, which is achieved by the association-disassociation transition of molecular chains. In the elongational field, both SAP and HPAM-1 do not degrade mechanically, as opposed to the case of HPAM-2. More significantly, SAP can improve oil recovery up to 18.7%, which is around three times higher than that of HPAM-1. This self-adaptive concept may open a new pathway for the molecular design of polymers used for enhancing oil recovery in low-permeability reservoirs.

Studying the mechanisms of natural rubber pyrolysis gas generation using RMD simulations and TG-FTIR experiments

Abstract Based on pyrolysis technology, natural rubber can be converted to gases of high calorific value and then be used as fuels. In order to further explain the generation mechanisms of natural rubber pyrolysis gas, a combination of reaction molecular dynamics (RMD) simulations and thermogravimetry-infrared spectroscopy (TG-FTIR) experiments were used to study the pyrolysis process. The results show that the pyrolysis gases include CH4, C2H4 and a small amount of C3H6 and C4H6. The TG-FTIR also shows the presence of CH4 and functional groups ( C H, CH2, CH3 and C C ) in C2H4, C3H6 and C4H8. The kinetics data of each reaction which obtained based on the chain reaction mechanism and transition state theory, were input into Aspen Plus® process simulations to further get reasonable reaction path. The simulation results show that CH3 separated from the main chain abstracts H from other molecules to generate CH4, while C2H4 is mainly generated by the breaking of C C bonds on long chains. Other small gas molecules are generated by the breaking up of large olefins or free radicals with low activity. This study provides a theoretical basis for the recycling of pyrolysis gas and may ultimately help to increase the energy efficiency of the pyrolysis process.

Consideration of Medical and Public Health Coordination - Experience from the 2016 Kumamoto, Japan Earthquake.

The aim of this study was to identify disaster medical operation improvements from the 2016 Kumamoto Earthquake (Kumamoto Prefecture, Japan) and to extract further lessons learned to prepare for future expected major earthquakes. The records of communications logs, chronological transitions of chain of command, and team registration logs for the Disaster Medical Assistant Team (DMAT), as well as other disaster medical relief teams, were evaluated. A total of 466 DMAT teams and 2,071 DMAT team members were deployed to the Kumamoto area, and 1,894 disaster medical relief teams and 8,471 disaster medical relief team member deployments followed. The DMAT established a medical coordination command post at several key disaster hospitals to designate medical coverage areas. The DMAT evacuated over 1,400 patients from damaged hospitals, transported medical supplies to affected hospitals, and coordinated 14 doctor helicopters used for severe patient transport. To keep constant medical and public health operations, DMAT provided medical coordination management until the local medical coordination was on-track. Several logistic teams, which are highly trained on operation and management of medical coordination command, were dispatched to assist management operation. The DMAT also helped to establish Disaster Coordination and Management Council at the prefectural- and municipal-level, and also coordinated command control for public health operations. The DMAT could provide not only medical assistance at the acute phase of the disaster, but also could provide medical coordination for public health and welfare. During the 2016 Kumamoto Earthquake, needs of public health and welfare increased enormously due to the sudden evacuation of a large number of residents. To provide constant medical assistance at the disaster area, DMAT, logistic teams, and other disaster medical relief teams must operate constant coordination at the medical headquarter command. For future expected major earthquakes in Japan, it will be required to educate and secure high enough numbers of disaster medical assistance and health care personnel to provide continuous medical and public health care for the affected area residents.Kondo H, Koido Y, Kawashima Y, Kohayagawa Y, Misaki M, Takahashi A, Kondo Y, Chishima K, Toyokuni Y. Consideration of medical and public health coordination - experience from the 2016 Kumamoto, Japan Earthquake. Prehosp Disaster Med. 2019;34(2):149-154.

PE-1 Vaginal microbiota composition and persistent high-risk HPV infection in HIV negative and HIV positive women

Background: Reports from previous studies suggest that the vaginal microbiota may play a role in cervical HPV pathogenesis. In this study, we examined associations between the vaginal microbiome and persistent high-risk human papillomarvirus (hrHPV) infection among HIV-negative and HIV-positive women. Methods: We used 16S rRNA gene amplicon sequencing to characterize the vaginal microbiota in 2 serial mid-vaginal samples taken approximately 6 months apart in 211 Nigerian women and the SPF10LIPA25 system for HPV detection. We used generalized estimating equation (GEE) logistic regression models with robust variance estimation and the cluster option for repeated measures, to evaluate the association between the vaginal microbiota composition and persistent hrHPV infection (defined as being positive for hrHPV at 2 visits 6 months apart); Linear discriminant analysis effect size (LEfSe) to identify phylotype biomarkers of persistent hrHPV; Markov chain transition probabilities to evaluate transition patterns and hierarchical clustering algorithms for community state (CST) assignments. Results: Some 142 women were HIV-positive and 69 were HIV-negative. Of the 211 participants, 71 were persistently positive for hrHPV. Mean age (SD) of participants was 38 (8) years. Most participants (84%, 175/211) were premenopausal. High diversity, low Lactobacillus spp. bacterial community state types, CST IV (A and B) were the most prevalent community state types (CST) in HIV-negative (57% at baseline and 40% at the follow-up visit) and HIV-positive (73% at baseline and 65% at the follow-up visit) women. There was effect modification by HIV status (P = 0.02). Among HIV-negative women, those who had a high relative abundance of Lactobacillus spp. were less likely to have persistent hrHPV (OR: 0.35, 95% CI: 0.14 to 0.89, P = 0.03) compared to women with low relative abundance of Lactobacillus spp. LEfSe analysis identified Sneathia spp as being differentially more abundant in HIV-negative women with persistent hrHPV. Markov chain transition probabilities showed that most CST transitions were to the highly diverse, low Lactobacillus spp., CST IV. In HIV-positive women, there was no significant association between the relative abundance of Lactobacillus spp and persistent hrHPV. Conclusions: Our results provide evidence to suggest that persistent hrHPV is associated with a lack of Lactobacillus spp in the vaginal microbiota of HIV-negative women.