Effects of electrospinning parameters on polyacrylonitrile nanofiber diameter: an investigation by response surface methodology

Effects of material and process parameters on the diameter of electrospun polyacrylonitrile fibers were experimentally investigated. Response surface methodology (RSM) was utilized to design the experiments at the settings of solution concentration, voltage and the collector distance. It also imparted the evaluation of the significance of each parameter on the resultant fiber diameter. The investigations were carried out in the two-variable process domains of several collector distances as applied voltage and the solution concentration were varied at a fixed polymer molecular weight. The mean diameter and coefficient of variation were modeled by polynomial response surfaces as functions of solution concentration and voltage at each collector distance. Effect of applied voltage in micron-scale fiber diameter was observed to be almost negligible when solution concentration and collector distance were high. However, all three factors were found statistically significant in the production of nano-scale fibers. The response surface predictions revealed the parameter interactions for the resultant fiber diameter, and showed that there is a negative correlation between the mean diameter and coefficient of variation for the fiber diameter. A sub-domain of the parameter space consisting of the solution concentration, applied voltage and collector distance, was suggested for the potential nano-scale fiber production

Distribution of fibers in SFRC segments for tunnel linings

This paper presents research results regarding the distribution of steel fibers in concrete used to build precast tunnel segments for Line 9 of the Barcelona Metro. The fiber distribution was studied using the actual fiber contents obtained by means of crushed cores drilled from different points of three full-scale tunnel lining segments. A statistical analysis determined that the fiber content in the ends of segments tends to be greater than in the central zone. The way of transporting, pouring and compacting concrete influences the fiber content and the fiber distribution across the thickness of the segment. In addition, cores with a diameter of 150 mm were found to have a lower scatter in the fiber content than smaller diameter specimens. Finally, based on probabilistic approaches, a minimum of 11 cores is proposed to control the fiber content in FRC segments.Peer ReviewedPostprint (author's final draft

Weekly Versus Monthly Testosterone Administration On Fast and Slow Skeletal Muscle Fibers in Older Adult Males

Context: In older adults, loss of mobility due to sarcopenia is exacerbated in men with low serum T. T replacement therapy is known to increase muscle mass and strength, but the effect of weekly (WK) vs monthly (MO) administration on specific fiber types is unknown. Objective: To determine the efficacy of WK vs MO T replacement on the size and functional capacity of individual fast and slow skeletal muscle fiber types. Design, Setting, and Patients: Subjects were randomized into a 5-month, double-blind, placebo-controlled trial. All subjects (ages, 61–71 y) were community-dwelling men who had T levels \u3c 500 ng/dL. Intervention: Subjects were dosed weekly for 5 months, receiving continuous T (WK, n = 5; 100 mg T enanthate, im injection), monthly cycled T (MO, n = 7; alternating months of T and placebo), or placebo (n = 7). Muscle biopsies of the vastus lateralis were obtained before and after treatment. Main Outcome Measures: Main outcomes for individual slow and fast fibers included fiber diameter, peak force (P0), rate of tension development, maximal shortening velocity, peak power, and Ca2+ sensitivity. Results: Both treatments increased fiber diameter and peak power, with WK treatment 5-fold more effective than MO in increasing type I fiber P0. WK effects on fiber diameter and force were 1.5-fold higher in slow fibers compared to fast fibers. In fast type II fibers, diameter and P0 increased similarly between treatments. The increased power was entirely due to increased fiber size and force. Conclusions: In conclusion, T replacement effects were fiber-type dependent, restricted to increases in cell size, P0, and peak power, and dependent on the paradigm selected (WK vs MO)

A Test Resonator for Kagome Hollow-Core Photonic Crystal Fibers for Resonant Rotation Sensing

We build ring resonators to assess the potentialities of Kagome Hollow-Core Photonic Crystal Fibers for future applications to resonant rotation sensing. The large mode diameter of Kagome fibers permits to reduce the free space fiber-to-fiber coupling losses, leading to cavities with finesses of about 30 for a diameter equal to 15 cm. Resonance linewidths of 3.2~MHz with contrasts as large as 89\% are obtained. Comparison with 7-cell photonic band gap (PBG) fiber leads to better finesse and contrast with Kagome fiber. Resonators based on such fibers are compatible with the angular random walk required for medium to high performance rotation sensing. The small amount of light propagating in silica should also permit to further reduce the Kerr-induced non-reciprocity by at least three orders of magnitudes in 7-cell Kagome fiber compared with 7-cell PBG fiber

Optical nanofibers and spectroscopy

We review our recent progress in the production and characterization of tapered optical fibers with a sub-wavelength diameter waist. Such fibers exhibit a pronounced evanescent field and are therefore a useful tool for highly sensitive evanescent wave spectroscopy of adsorbates on the fiber waist or of the medium surrounding. We use a carefully designed flame pulling process that allows us to realize preset fiber diameter profiles. In order to determine the waist diameter and to verify the fiber profile, we employ scanning electron microscope measurements and a novel accurate in situ optical method based on harmonic generation. We use our fibers for linear and non-linear absorption and fluorescence spectroscopy of surface-adsorbed organic molecules and investigate their agglomeration dynamics. Furthermore, we apply our spectroscopic method to quantum dots on the surface of the fiber waist and to caesium vapor surrounding the fiber. Finally, towards dispersive measurements, we present our first results on building and testing a single-fiber bi-modal interferometer.Comment: 13 pages, 18 figures. Accepted for publication in Applied Physics B. Changes according to referee suggestions: changed title, clarification of some points in the text, added references, replacement of Figure 13

Processing of carbon-fiber-reinforced Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass composites

Carbon-fiber-reinforced bulk metallic glass composites are produced by infiltrating liquid Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 into carbon fiber bundles with diameter of the individual fiber of 5 mum. Reactive wetting occurs by the formation of a ZrC layer around the fibers. This results in a composite with a homogeneous fiber distribution. The volume fraction of the fibers is about 50% and the density of the composite amounts to 4.0 g/cm(^3)

Development of fine diameter mullite fiber

Results are presented of a program to develop and evaluate mullite fiber with a mean diameter under two microns. The two micron fiber is produced by a blowing process at room temperature from a low viscosity (10-25 poise) solution. The blown fiber was evaluated for dimensional stability in thermal cycling to 1371 C, and was equivalent to the 5 micron spun B and W mullite fiber. An additive study was conducted to evaluate substitutes for the boron. Three levels of chromium, lithium fluoride, and magnesium were added to the standard composition in place of boron and the fiber produced was evaluated for chemical and dimensional stability in thermal cycling to 1371 C. The magnesium was the most chemically stable, but the chrome additive imparted the best dimensional stability

Deformation of a flexible fiber in a viscous flow past an obstacle

We study the deformation and transport of elastic fibers in a viscous Hele-Shaw flow with curved streamlines. The variations of the global velocity and orientation of the fiber follow closely those of the local flow velocity. The ratios of the curvatures of the fibers by the corresponding curvatures of the streamlines reflect a balance between elastic and viscous forces: this ratio is shown experimentally to be determined by a dimensionless {\it Sperm number} $Sp$ combining the characteristic parameters of the flow (transverse velocity gradient, viscosity, fiber diameter/cell gap ratio) and those of the fiber (diameter, effective length, Young's modulus). For short fibers, the effective length is that of the fiber; for long ones, it is equal to the transverse characteristic length of the flow. For $S\_p \lesssim 250$, the ratio of the curvatures increases linearly with $Sp$; For $S\_p \gtrsim 250$, the fiber reaches the same curvature as the streamlines

Advanced tungsten fiber-reinforced nickel superalloy

Matrix composition, fabrication technique, and fiber diameter were selected to minimize fiber-matrix reaction and preserve composite strength. Composites may be used in place of superalloys where higher strength or greater strength-to-density ratios are advantageous, and will permit higher operating temperatures in particular applications