Surface Tension Measurement of Polystyrene in Supercritical Fluids

Interfacial tension provides valuable information about polymer processes such as foaming, particle (pigment) suspension, wetting, and blending. Among the methods commonly used to measure surface tension, drop shape methods entail several advantages such as simplicity and versatility. The profile of the drop, which is determined by the balance between gravity and surface forces, is easily defined. The surface tension is obtained from the profile of the drop. Recent progress in image analysis and data acquisition systems makes it possible to digitalize drop images directly using a video frame grabber with a digital camera. The digital signals are easily analyzed using different algorithms to determine the surface/interfacial tension from the drop profile. This study concentrates on one of the drop methods, the pendant drop method, which involves the determination of a drop profile of one dense liquid suspended in another liquid at mechanical equilibrium. Despite theoretical simplicity of using sessile and pendant drops for determining the surface tension of polymer melts, research in this area is limited because of the experimental difficulty associated with maintaining equilibrium of highly viscous melts. This paper examines the surface tension of polystyrene melts using Axisymmetric Drop Shape Analysis (ADSA) at high temperatures. This thesis focuses on attaining a stable pendant drop during experiments and modifying experimental designs. The method is verified by experiments in the air and nitrogen, where reproducibility tests and statistical analyses are performed. The surface tension of polystyrene (PS) that melts in supercritical carbon dioxide is obtained while the gas solubility is correlated with the surface tension value determined under various conditions. The Sanchez-Lacombe (S-L) equation of state (EOS) is applied to estimate the Pressure-Volume-Temperature (PVT) data of the PS/supercritical-carbon-dioxide mixtures, which gives density data. The relationship between surface tension and density is described by the empirical Macleod equation. To characterize the stability of pendant drops formed by the polymer melt, the Bond number is found to be useful; in particular, a stable pendant drop is obtained when the Bond number is between 0.4 and 0.8. This thesis presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendant drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and a good agreement with the experiment is obtained. The physical mechanisms for three main experimental trends are explained using SCFT, and none of the explanations depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the rate of surface tension change with temperature is dependent on pressure. A linear relationship is found between surface tension and temperature, and between surface tension and pressure within a temperature range of 170-210C and a pressure range of 500-2,000 psi. Two monodisperse polystyrenes of Mw ~ 100,000 and Mw ~400,000 and a polydisperse polystyrene were investigated to show the temperature and pressure effect on the surface tension in supercritical nitrogen. Regardless of the molecular weight and polydispersity, the surface tension of polystyrenes decreases as the pressure and temperature increase. Monodisperse polystyrene of a higher molecular weight has a higher surface tension by 6-9 mJ/m2 at each experimental condition. The surface tension dependence on temperature and on pressure is more significant for the higher molecular weight polystyrene; the surface tension has been varied more in the higher molecular weight polystyrene than in the lower molecular weigh polystyrene. For a polydisperse polystyrene, high surface tension values seem to be determined predominantly by its high molecular weight portion of polystyrene molecules. An empirical equation was generated to relate surface tension to the density difference between the polymer and supercritical nitrogen. This research should have implications in understanding polymer foaming processes and have application in various polymer engineering fields including polymer characterizations, polymer synthesis, and surface modifications

Requirement of estrogen receptor alpha DNA-binding domain for HPV oncogene-induced cervical carcinogenesis in mice

Cervical cancer is caused by human papillomavirus (HPV) in collaboration with other non-viral factors. The uterine cervix is hormone responsive and female hormones have been implicated in the pathogenesis of the disease. HPV transgenic mice expressing HPV16 oncogenes E6 ( K14E6 ) and/or E7 ( K14E7 ) have been employed to study a mechanism of estrogen and estrogen receptor ? (ER?) in cervical carcinogenesis. A chronic exposure to physiological levels of exogenous estrogen leads to cervical cancer in the HPV transgenic mice, which depends on ER?. The receptor is composed of multiple functional domains including a DNA-binding domain (DBD), which mediates its binding to estrogen-responsive elements (EREs) on target genes. A transcriptional control of genes by ER? is mediated by either DBD-dependent (classical) or DBD-independent (non-classical) pathway. Although molecular mechanisms of ER? in cancer have been characterized extensively, studies investigating importance of each pathway for carcinogenesis are scarce. In this study, we employ knock-in mice expressing an ER? DBD mutant (E207A/G208A) that is defective specifically for ERE binding. We demonstrate that the ER? DBD mutant fails to support estrogen-induced epithelial cell proliferation and carcinogenesis in the cervix of K14E7 transgenic mice. We also demonstrate that cervical diseases are absent in K14E7 mice when one ER? DBD mutant allele and one wild-type allele are present. We conclude that the ER? classical pathway is required for cervical carcinogenesis in a mouse model

Short-Term Effects of Combined Serial Casting and Botulinum Toxin Injection for Spastic Equinus in Ambulatory Children with Cerebral Palsy

PURPOSE: The purpose of this paper is to test the hypothesis that combination therapy of serial cast and botulinum toxin type A (BTX-A) injection can further enhance the effects of a BTX-A injection in ambulant children with cerebral palsy (CP) who have an equinus foot. MATERIALS AND METHODS: Children in group A (30 legs of 21 children) received a serial casting application after an injection of BTX-A, and children in group B (25 legs of 17 children) received only a BTX-A injection. Assessments were performed before the intervention and 1 month after the intervention. RESULTS: After the intervention, there were significant improvements in tone, dynamic spasticity, and passive range of motion (ROM) in both groups. However, the changes were greater in group A than in group B. Dimension D (standing) in Gross Motor Function Measure (GMFM)-66 was significantly improved in group A but not in group B. On the other hand, there were no significant changes in dimension E (walking, running, jumping) in GMFM-66 in either group. CONCLUSION: The results of our study suggest that a serial casting application after BTX-A injection can enhance the benefits of BTX-A injection in children with cerebral palsy.ope

Quaternary semiconductor Cu2FeSnS4 nanoparticles as an alternative to Pt catalysts

We demonstrate an N719 dye sensitized solar cell based on Cu 2FeSnS4 (CFTS) as a counter electrode. The elements for the material are all earth abundant and environmentally benign. The power conversion efficiency of a DSSC using CFTS was comparable to that of a DSSC using Pt under A.M. 1.5G (100 mW cm-2).close3

Security of Cyber-Physical Systems in the Presence of Transient Sensor Faults

This paper is concerned with the security of modern Cyber-Physical Systems in the presence of transient sensor faults. We consider a system with multiple sensors measuring the same physical variable, where each sensor provides an interval with all possible values of the true state. We note that some sensors might output faulty readings and others may be controlled by a malicious attacker. Different from previous works, in this paper we aim to distinguish between faults and attacks and develop an attack detection algorithm for the latter only. To do this, we note that there are two kinds of faults – transient and permanent; the former are benign and short-lived whereas the latter may have dangerous consequences on system performance.We argue that sensors have an underlying transient fault model that quantifies the amount of time in which transient faults can occur. In addition, we provide a framework for developing such a model if it is not provided by manufacturers. Attacks can manifest as either transient or permanent faults depending on the attacker’s goal. We provide different techniques for handling each kind. For the former, we analyze the worst-case performance of sensor fusion over time given each sensor’s transient fault model and develop a filtered fusion interval that is guaranteed to contain the true value and is bounded in size. To deal with attacks that do not comply with sensors’ transient fault models, we propose a sound attack detection algorithm based on pairwise inconsistencies between sensor measurements. Finally, we provide a real-data case study on an unmanned ground vehicle to evaluate the various aspects of this paper