Preparation and characterization of carbon fibers from polyacrylonitrile precursors

The present work deals with the preparation of carbon fibers from polyacrylonitrile (PAN) fibers. The chemical composition and physical properties of the starting fibers were determined. The PAN fibers were stabilized in air at the temperatures (230, 270, and 300°C) with the heating time from 40 to 420 min. The effects of both final stabilization temperature and heating rate on the chemical and physical properties of the prepared stabilized fibers were studied. The chosen stabilized fibers samples were carbonized in argon atmosphere at the temperatures (1000, 1200, and 1400°C) with different heating rates 5, 10, 15, and 20°C min^?1. The effects of both carbonizing temperature and heating rate on the weight loss, density, elemental composition, and IR absorption spectra of carbonized fibers were also studied. The fiber sample, which was carbonized at 1400°C, contains 97.55% carbon, 1.75% nitrogen, and 1.4% hydrogen. This means that carbonizing the stabilized fibers at 1400°C in argon atmosphere is suitable to get oxygen‐free carbon fibers. Therefore, the used carbonizing temperature in the present work (1400°C) is suitable to produce moderate heat‐treated carbon fibers with the heating rate of 15°C min^?1. The modulus of the prepared carbon fibers was compared to that of industrially produced fibers using the results of X‐ray analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterizing the hierarchical structures of bioactive sol-gel silicate glass and hybrid scaffolds for bone regeneration

Bone is the second most widely transplanted tissue after blood. Synthetic alternatives are needed that can reduce the need for transplants and regenerate bone by acting as active temporary templates for bone growth. Bioactive glasses are one of the most promising bone replacement/regeneration materials because they bond to existing bone, are degradable and stimulate new bone growth by the action of their dissolution products on cells. Sol-gel-derived bioactive glasses can be foamed to produce interconnected macropores suitable for tissue ingrowth, particularly cell migration and vascularization and cell penetration. The scaffolds fulfil many of the criteria of an ideal synthetic bone graft, but are not suitable for all bone defect sites because they are brittle. One strategy for improving toughness of the scaffolds without losing their other beneficial properties is to synthesize inorganic/organic hybrids. These hybrids have polymers introduced into the sol-gel process so that the organic and inorganic components interact at the molecular level, providing control over mechanical properties and degradation rates. However, a full understanding of how each feature or property of the glass and hybrid scaffolds affects cellular response is needed to optimize the materials and ensure long-term success and clinical products. This review focuses on the techniques that have been developed for characterizing the hierarchical structures of sol-gel glasses and hybrids, from atomic-scale amorphous networks, through the covalent bonding between components in hybrids and nanoporosity, to quantifying open macroporous networks of the scaffolds. Methods for non-destructive in situ monitoring of degradation and bioactivity mechanisms of the materials are also included.     

Single molecular switch based on thiol tethered iron(II)clathrochelate on gold

Molecular electronics has been associated with high density nano-electronic devices. Developments of molecular electronic devices were based on reversible switching of molecules between the two conductive states. In this paper, self-assembled monolayers of dodecanethiol (DDT) and thiol tethered iron(II)clathrochelate (IC) have been prepared on gold film. The electrochemical and electronic properties of IC molecules inserted into the dodecanethiol monolayer (IC-DDT SAM) were investigated using voltammetric, electrochemical impedance spectrpscopy (EIS), scanning tunneling microscopy (STM) and cross-wire tunneling measurements. The voltage triggered switching behaviour of IC molecules on mixed SAM was demonstrated. Deposition of polyaniline on the redox sites of IC-DDT SAM using electrochemical polymerization of aniline was performed in order to confirm that this monolayer acts as nano-patterned semiconducting electrode surface.     

HEAT EFFECTS FOR PHYSICAL AND CHEMICAL ABSORPTION IN TURBULENT LIQUID FILMS

An eddy diffusivity model was used to describe simultaneous heat and mass transfer for chemical absorption in turbulent liquid films. For absorption accompanied by a first-order reaction an approximate expression for the mass transfer coefficient is derived and shown to be in excellent agreement with exact numerical calculations. An equation is developed for the temperature rise at the free surface due to both the heat of reaction and the heat of solution. Relationships are also developed for the concentration of the liquid phase product at the free surface and the depletion of the liquid phase reactant at the free surface.

The temperature rise at the free surface for gas absorption accompanied by an instantaneous reaction due to both the heat of solution and the heat of reaction was determined. An equation is also derived for the concentration of liquid phase product at the free surface for the case of an instantaneous reaction.     

Diode pumped operation of thulium doped fluoride fibre amplifiersuitable for first window systems

A fully connectorised diode laser pumped first window amplifier has been constructed, for the first time, around a thulium doped fluoride fibre. For a 780/806 nm combination of pump and signal wavelengths, small signal gains of 25-26 dB and gain efficiencies of 2.4 dB/mW have been achieved. In addition, output powers approaching +13 dBm are possible for a launched pump power of 31 mW, which corresponds to a conversion efficiency of around 650%     

Overexpression and large-scale purification of recombinant hamster polymorphic arylamine N-acetyltransferase as a dihydrofolate reductase fusion protein

N-Acetyltransferases (NATs) are enzymes that catalyze the detoxification and/or bioactivation of a variety of xenobiotics. Rapid kinetic, biophysical, structural, and bioactivation studies on NATs require quantities of purified enzyme capable of being obtained only through recombinant DNA technology. This laboratory has previously developed a protein expression and purification system in which NATs are expressed as proteins fused to a FLAG octapeptide followed by a thrombin-cleavage site to allow liberation of the rNAT. Typically, however, only 0.5-1.5 mg of the recombinant NAT's could be readily purified in a single isolation sequence by immunoaffinity chromatography. Therefore, the expression system was modified by inserting the L54F dihydrofolate reductase (DHFR) mutant gene sequence between the FLAG octapeptide and the thrombin-cleavage site. Expression was carried out with TOPP3 Escherichia coli cells. The new purification methodology utilizes the unique pH dependence of binding to a methotrexate (MTX)-affinity column by the L54F DHFR mutant. Unfortunately, the affinity chromatography strategy did not work satisfactorily. Although the specific activity of the purified rNAT2 was comparable to that of NAT2 obtained from hamster tissue, only 3% of the activity was recovered. The apparent cause of the low recovery is the unanticipated irreversible binding of rNAT2 to MTX. Ion-exchange chromatography was investigated as an alternative purification method. An initial DEAE anion-exchange column resulted in partial purification of the fusion protein. The fusion protein was cleaved with thrombin and reapplied to a DEAE anion-exchange column. The second DEAE column resulted in not only the separation of rNAT2-70D from FLAG-L54F DHFR, but also the purification of rNAT2-70D to near homogeneity. Application of the nearly homogeneous rNAT2-70D to a gel-filtration column resulted in recovery of homogeneous protein. The ion-exchange method of purifying rNAT2-70D is inexpensive and simple and yields more than 8 mg of pure enzyme from 1 liter of cell culture.     

Effect of curing conditions on the total water content of hardened portland cement paste

The effect of various curing conditions on the amount of water held by pastes with low water/cement ratios was investigated. It was concluded from the results that factors significantly influencing the total water content of a cement paste made with ordinary Portland cement and cured at room temperature are: water/cement ratio, curing medium, curing period and curing history.     

An advanced start algorithm for all-integer programming

In this paper, we present an all-integer cutting plane technique called the Advanced Start Algorithm (ASA), for solving the all-integer (otherwise linear) programming problem (IP). We develop a good advanced primal-infeasible start based on the optimal solution to the LP relaxation, and use a two-stage dual/primal algorithm to obtain the optimal solution to (IP). We illustrate the operation of the ASA on three small problems, and exhibit computational results on a set of standard test problems.     

Effect of moisture content of raw materials on the viscosity of limestone–marl slurry

Viscosity measurements were performed to investigate the effect of moisture contained in Portland cement raw materials on the flow characteristics of limestonemarl slurry. Under conditions of constant total water content, the fluidity of the slurry increased as the moisture content of the raw materials decreased. The effect of moisture content of the raw materials becomes significant on reducing the water content of the slurry. In the presence of slurry thinners, the extent of deflocculation is greater with the raw materials of lower moisture content.