Continuous polyacrylonitrile nanofiber yarns: Preparation and dry-drawing treatment for carbon nanofiber production

Precursor fibers with diameters in nanometer scale and highly aligned polymer chains in fibers are highly promising for the preparation of high-performance carbon nanofibers, but are challenging to make. In this study, we demonstrate for the first time that a carbon nanofiber precursor can be prepared by the electrospinning of polyacrylonitrile into a nanofiber yarn and by the subsequent drawing treatment of the yarn in dry conditions. The yarn shows excellent drawing performance, which can be drawn evenly up to 6 times of its original length without breaking. The drawing treatment improves the yarn and fiber uniformity, polymer chain orientation within the fibers, as well as yarn tension and modules, but shows decreased yarn and fiber diameter and elongation at break. The drawing temperature and force show influences on the drawing behavior. The highest strength and modules (362 ± 37 MPa and 9.2 ± 1.4 GPa, respectively) are found on the yarn drawn by 5 times its length, which increased by 800% and 1800% when compared to the as-spun yarn. Through un-optimized stabilization and carbonization treatments, we further demonstrate that the carbonized nanofiber yarn shows comparable tensile properties as the commercial carbon fibers. Electrospun nanofiber yarns may form next generation precursors for making high performance carbon fibers. This journal is

The epidemiology of dry eye in Melbourne, Australia

OBJECTIVE: To describe the epidemiology of dry eye in the adult population of Melbourne, Australia. DESIGN: A cross-sectional prevalence study. PARTICIPANTS: Participants were recruited by a household census from two of nine clusters of the Melbourne Visual Impairment Project, a population-based study of age-related eye disease in the 40 and older age group of Melbourne, Australia. Nine hundred and twenty-six (82.3% of eligible) people participated; 433 (46.8%) were male. They ranged in age from 40 to 97 years, with a mean of 59.2 years. MAIN OUTCOME MEASURES: Self-reported symptoms of dry eye were elicited by an interviewer-administered questionnaire. Four objective assessments of dry eye were made: Schirmer's test, tear film breakup time, rose bengal staining, and fluorescein corneal staining. A standardized clinical slit-lamp examination was performed on all participants. Dry eye for the individual signs or symptoms was defined as: rose bengal > 3, Schirmers < 8, tear film breakup time < 8, > 1/3 fluorescein staining, and severe symptoms (3 on a scale of 0 to 3). RESULTS: Dry eye was diagnosed as follows: 10.8% by rose bengal, 16.3% by Schirmer's test, 8.6% by tear film breakup time, 1.5% by fluorescein staining, 7.4% with two or more signs, and 5.5% with any severe symptom not attributed to hay fever. Women were more likely to report severe symptoms of dry eye (odds ratio [OR] = 1.85; 95% confidence limits [CL] = 1.01, 3.41). Risk factors for two or more signs of dry eye include age (OR = 1.04; 95% CL = 1.01, 1.06), and self-report of arthritis (OR = 3.27; 95% CL = 1.74, 6.17). These results were not changed after excluding the 21 people (2.27%) who wore contact lenses. CONCLUSIONS: These are the first reported population-based data of dry eye in Australia. The prevalence of dry eye varies by sign and symptom.

Qualitative assessment of bubble behaviour for central and asymmetric injection in 2D gas-solid fluidized bed using image analysis technique and CFD modelling

Bubble characteristics such as shape, size, and trajectory control the hydrodynamics and therefore heat transfer in fluidized bed reactors. Thus understanding these characteristics is very important for the design and scaleup of fluidized beds. An earlier developed Eulerian-Eulerian two-fluid model for simulating dense gas–solid two-phase flow has been used to compare the experimental data in a pseudo-two-dimensional (2-D) bed. Bubbles are injected asymmetrically by locating the nozzle at proximity to the wall, thus presenting the effect wall has on asymmetrical injection as compared to symmetrical injection. In this work, a digital image analysis technique was developed to study the bubble behaviour in a two-dimensional bubbling bed. The high-speed photography reveals an asymmetric wake formation during detachment indicating an early onset of mixing process. The wall forces acts tangentially on thebubble and has a significant impact on the bubble shape, neck formation during detachment and its trajectory through the bed. Larger bubbles drifting away from the centre with longer paths are observed. This qualitative behaviour is well predicted by CFD modelling. Asymmetric injection can significantly influence the heat and mass transfer characteristics.

Bubble flow in a static magnetic field

A lab-based electrolytic-cell is designed to analyze the effect of external magnetic field on bubble evolution underneath an anode surface. Buckingham Pi theorem is used to provide a complete list of dimensionless parameters for a typical cell configuration. There is an increase in bubble size and the number of bubbles with time. The hydrodynamic convection is apparent due to the effect of electrolyte flow caused by swarm of bubbles rising along the anode surface. The image sequence shows that swarm of bubbles exhibit a swirling flow-field in the presence of the magnetic field. The coalescence process intensifies in an area where magnetic field is higher. As a consequence, bubbles are swept away by the magneto-hydrodynamic (MHD) convection. These results suggest that a magnetic field causes remarkable improvement on the surface coverage of the anode.