New Classes of Self-Assembled Structures in Nonpolar Solvents

Many researchers have investigated the self-assembly of amphiphilic molecules in water into characteristic structures such as micelles and vesicles. In comparison, amphiphilic self-assembly in nonpolar organic liquids, which can be referred to as "reverse" self-assembly, is much less studied. In this dissertation, we describe a variety of new reverse self-assembled structures formed from amphiphilic molecules. Especially, we focus on long reverse cylindrical structures that can induce high viscosity, and reverse vesicles, i.e., hollow spherical containers surrounded by reverse bilayers. We expect that these reverse structures may be useful for applications such as gelling agents for fuels and oils, hosts for enzymatic reactions, and controlled release. In the first part of this study, we describe the effects of adding inorganic salts to solutions of lecithin in nonpolar solvents. Lecithin is a zwitterionic, mono-unsaturated phospholipid that by itself forms reverse spherical micelles. Salts can be dissolved in these solvents in the presence of lecithin. Interestingly, salts of multivalent cations like calcium (Ca2+), magnesium (Mg2+), lanthanum (La3+) and cerium (Ce3+) greatly increase the viscosity of lecithin sols and transform them into optically transparent organogels. In comparison, monovalent cations or transition-metal cations have negligible effect on reverse self assembly. Based on data from small-angle neutron scattering (SANS), we show that gelation is accompanied by a transition from spherical micelles to cylindrical micelles/filaments. The varying abilities of different cations to induce gelation is shown to correlate with their binding tendencies to the phosphocholine headgroups of lecithin. Next, we describe a class of photorheological (PR) fluids based on a nonpolar solvent such as cyclohexane. The rheological properties of these fluids can be reversibly tuned by UV and visible light. In order to create such PR fluids, reverse wormlike micelles of lecithin + sodium deoxycholate (SDC) are doped with a photoresponsive compound, spiropyran (SP). Spiropyrans can be reversibly converted from a closed-form (SP) to an open-form (MC) by UV and visible light, respectively. Initially, the reverse micelles in the lecithin/SDC/SP system are long and entangled, which makes the solution highly viscous. When exposed to UV light, the viscosity of these micellar solutions drops by a factor of 10. Conversely, when exposed to visible light, the viscosity recovers to approximately its initial value. We have found that this cycle between high and low viscosity states can be repeated more than 10 times. Finally, we describe a new route to forming bilayered structures such as reverse vesicles and lamellae in organic solvents such as cyclohexane. This involves the combination of a saturated phospholipid, dimyristoyl phosphatidyl choline (DMPC) with an inorganic salt having either a trivalent cation like gadolinium (Gd3+) or a divalent cation like calcium (Ca2+). We find that the addition of the salt to DMPC solutions leads to either cylindrical aggregates or bilayered aggregates depending on the concentration of the salt. The structural changes can be explained qualitatively in terms of changes in the molecular geometry (packing parameter) induced by the binding of cations to the headgroups of the phospholipid

Increased Risk of Ischemic Stroke during Sleep in Apneic Patients.

BACKGROUND AND PURPOSE:The literature indicates that obstructive sleep apnea (OSA) increases the risk of ischemic stroke. However, the causal relationship between OSA and ischemic stroke is not well established. This study examined whether preexisting OSA symptoms affect the onset of acute ischemic stroke. METHODS:We investigated consecutive patients who were admitted with acute ischemic stroke, using a standardized protocol including the Berlin Questionnaire on symptoms of OSA prior to stroke. The collected stroke data included the time of the stroke onset, risk factors, and etiologic subtypes. The association between preceding OSA symptoms and wake-up stroke (WUS) was assessed using multivariate logistic regression analysis. RESULTS:We identified 260 subjects with acute ischemic strokes with a definite onset time, of which 25.8% were WUS. The presence of preexisting witnessed or self-recognized sleep apnea was the only risk factor for WUS (adjusted odds ratio=2.055, 95% confidence interval=1.035-4.083, p=0.040). CONCLUSIONS:Preexisting symptoms suggestive of OSA were associated with the occurrence of WUS. This suggests that OSA contributes to ischemic stroke not only as a predisposing risk factor but also as a triggering factor. Treating OSA might therefore be beneficial in preventing stroke, particularly that occurring during sleep

Hot electron effects and electric field scaling near the metal-insulator transition in multilayer MoS2

The layered transition metal dichalcogenides have emerged as valuable platforms to study the challenging problem of metal-insulator transition in two dimensions. It was demonstrated that multilayer MoS2 exhibits clearly distinctive metallic and insulating behaviors in conductivity in response to both temperature and the electric field. Here, we report on the scaling analyses of conductivity for the electric field in addition to the temperature, which is performed with the consideration of electron-electron interactions for multilayer MoS2. Based on the analysis of hot electron effects in the electric field, we find that scaling for the electric field is relevant for the metallic phase in the high-field regime, enabling one to extract the dynamical critical exponent z close to 1. This result supports that the metal-insulator transition in multilayer MoS2 is a true quantum critical phenomenon, in which strong interactions induce the transition. ©2020 American Physical Society11sciescopu

Reducing Confusion about Grounded Theory and Qualitative Content Analysis: Similarities and Differences

Although grounded theory and qualitative content analysis are similar in some respects, they differ as well; yet the differences between the two have rarely been made clear in the literature. The purpose of this article was to clarify ambiguities and reduce confusion about grounded theory and qualitative content analysis by identifying similarities and differences in the two based on a literature review and critical reflection on the authors’ own research. Six areas of difference emerged: (a) background and philosophical base, (b) unique characteristics of each method, (c) goals and rationale of each method, (d) data analysis process, (e) outcomes of the research, and (f) evaluation of trustworthiness. This article provides knowledge that can assist researchers and students in the selection of appropriate research methods for their inquiries

Comparison of Heat and Moisture Fluxes from a Modified Soil-plant-atmosphere Model with Observations from BOREAS

This study evaluates the prediction of heat and moisture fluxes from a new land surface scheme with eddy correlation data collected at the old aspen site during the Boreal Ecosystem-Atmosphere Study (BOREAS) in 1994. The model used in this study couples a multilayer vegetation model with a soil model. Inclusion of organic material in the upper soil layer is required to adequately simulate exchange between the soil and subcanopy air. Comparisons between the model and observations are discussed to reveal model misrepresentation of some aspects of the diurnal variation of subcanopy processes. Evapotranspiratio

Chronic active EBV infection: the experience of the Samsung Medical Center in South Korea

AbstractBackgroundChronic active EBV infection (CAEBV) of T-cell or NK-cell type is an EBV+ polyclonal, oligoclonal or often monoclonal lymphoproliferative disorder (LPD) recognized as representing the spectrum of EBV-associated T-cell and NK-cell LPD with different clinical presentations; one systemic and two cutaneous disorders including hydroa vacciniforme-like T-cell LPD and mosquito bite hypersensitivity. The systemic form of the disease is characterized by fever, persistent hepatitis, hepatosplenomegaly and lymphadenopathy, which shows varying degrees of clinical severity depending on the immune response of the host and the EBV viral load.Case reportsWe described the clinicopathological findings of two children with CAEBV with a brief review of the literature.ConclusionsRecognition of the disease is important for adequate management of the patient. EBV analysis should be included in the principal diagnostic tests for febrile children