A simplified high-performance liquid chromatographic method for direct determination of warfarin enantiomers and their protein binding in stroke patients

A simplified method for direct determination of warfarin enantiomers by high-pressure liquid chromatography with fluorescence detection has been developed. This method involves solid phase extraction of warfarin in plasma, precolumn derivatization to form diastereoisomeric esters, and post-column reaction to discriminate each enantiomer separately. Ultrafiltration was employed in the separation of unbound warfarin enantiomers. Twelve plasma samples from six stroke patients taking warfarin regularly were analyzed. The average concentration of total warfarin was 0.47 +/- 0.17 mg/L for the S-isomer and 0.69 +/- 0.18 mg/L for the R-isomer. The average protein binding was 99.67 +/- 0.33% for S-warfarin and 99.44 +/- 0.33% for R-warfarin. This methodology provides a quick and reliable technique for determining enantiomeric protein binding of warfarin in clinical settings.     

Synthesis of a novel small diameter polyurethane vascular graft with reactive binding sites

Development of a small diameter (4 mm inner diameter [ID]) prosthetic vascular graft with functional groups accessible for covalent binding of recombinant hirudin (a potent anticoagulant) should create a more hemocompatible surface. The purpose of this study was to develop a technique for generating carboxylic acid groups on the surface of precast 4 mm ID poly-(carbonate urea)-urethane vascular grafts and to evaluate the accessibility of these groups. A polycarbonate based urethane with the chain extender 2,2-bis(hydroxymethyl)propionic acid was synthesized. A precast 4 mm ID poly(carbonate urea)-urethane vascular graft (Chronoflex [CF]; CardioTech International, Woburn, MA) was then placed into a 4% carboxylated polyurethane (cPU) solution (in 1% dimethyl acetamide) and incubated for 30 minutes (cPU graft). To determine the accessibility of the carboxylic acid groups, a standard textile technique using methylene blue dye was used. Macroscopic cross-sections, which were cut and evaluated for dye penetration, showed greatest concentration of carboxylic acid groups at the luminal and capsule surfaces, with minimal penetration into the mid-portion of the graft. Analysis of dye baths for absorbance reduction resulted in the cPU grafts having 3.7-fold and 5.4-fold more accessible carboxylic acid groups compared with untreated and dimethyl acetamide dipped CF grafts. Thus, a novel small diameter vascular graft has been developed that contains reactive carboxylic acid groups accessible for protein binding.     

Pt based nanocomposites (mono/bi/tri-metallic) decorated using different carbon supports for methanol electro-oxidation in acidic and basic media

Pt based mono/bi/tri-metallic nanocomposites on different carbon based supports (activated carbon (AC), carbon nanotubes (CNTs) and carbon nanofibers (CNFs)) were synthesised and Pt surface enrichment achieved. The overall theoretical metallic content (Pt + Au + Sn) was 20% (w/w) in all mono/bi/tri-metallic nanocomposites and was found to be uniformly distributed in the supporting matrix (80%). The surface morphology and composition of the synthesised materials was characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while cyclic voltammetry was employed in order to confirm their typical metallic electrochemical characteristics. Electrochemical measurements indicated that Pt(2)Au(1)Sn(1) trimetallic catalysts demonstrated a significantly higher electrochemically active surface area relative to activated carbon supported PtAu based bimetallic counterparts. The results show that the CNT based trimetallic catalyst (Pt(2)Au(1)Sn(1)/CNT) showed greatest electroactive surface area (49.3 m(2)/g) and current density for methanol oxidation in acidic (490 mA mg(-1) Pt) as well as basic (1700 mA mg(-1) Pt) conditions. Results demonstrated that in comparison to Au/C and Sn/C (no/negligible response), the presence of a small amount of Pt in the Au and Sn based nanocomposites, significantly modified the catalytic properties. The activated carbon supported bimetallic (Pt(1)Au(3)/C) catalyst showed reasonably good response (260 mA mg(-1) Pt) among all bimetallic nanomaterials examined. The current response achieved for Pt(2)Au(1)Sn(1)/CNT was 1.9 times (in acidic media) and 2.1 times (in basic media) that for synthesised Pt/C in terms of per mg Pt activity. Overall the methanol oxidation studies demonstrated that the presence of Au and Sn in Pt based catalysts strongly indicated their capacity to reduce the precious Pt content required for this application, demonstrating the role of Au in improving current/potential response and signifying the importance of supporting matrices.     

Fracture resistance determination of freshwater ice using a chevron notched tension specimen

Crack growth resistance (R-curve behavior) measurements on large grained S1 type freshwater ice were conducted in the Ice Mechanics Research Laboratory at Clarkson University. To overcome previous difficulties in obtaining stable cracking in freshwater ice, a new crack geometry was developed. The short rod Chevron Notched Tension (CNT) specimen was found to be extremely favorable in the sense of promoting stable,stick-slip, crack growth over a large portion of the uncracked ligament. A negative fracture resistanceK _R -curve was evaluated for this ice at -16°C.     

A broad-spectrum constitutive modeling technique applied to saline ice

The constitutive behavior of lab-grown saline ice subjected to isothermal, uniaxial tensile loadings is discussed. A rectangular plate specimen of S2 columnar saline ice was subjected to a uniform tensile stress perpendicular to the long axis of the column structure. This loading was selected to represent the stress field which occurs in the plane of natural ice covers under tension. The uniaxial stress state was applied with a recently developed, modified Reversed Direct Stress device. Two successive load histories were applied – creep-recovery cycles and monotonic stress ramps. A broad-spectrum, nonlinear viscoelastic modeling approach is used to develop a constitutive model of the strain response. Each parameter of the model is evaluated from the measured ice response to the creep-recovery loadings. The model provides an accurate representation of the experimental data with a delayed elastic compliance function in time power law form (t _n ,n= ) and a nonlinear stress exponent (σ _q ,q = ). Finally, the model is used to predict the strain response of the ice to the monotonic ramp loadings with good results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tantalum silicide films deposited by dc sputtering

Tantalum disilicide films were deposited by conventional dc sputtering from a nominally stoichiometric cathode. The film characteristics were analyzed by x-ray diffraction, backscatter-ing, electron microprobe and electron transmission microsco-py. The film resistivity and stresses were also measured. The effects of heat treatments up to 1000°C were systematically investigated. After a 1000°C anneal, resistivities of 45-60 μΩcm can be achieved reproducibly. Films deposited on sili-con can be oxidized in a steam atmosphere without inducing significant changes in the silicide layer itself. An attempt is made to explain the oxidation behavior in terms of kinetic factors.     

Electrical and computer engineering curriculum assessment via senior miniproject

Traditionally, senior capstone projects have been used for comprehensive student assessment. Other mechanisms exist for engineering course assessments, such as teacher/course evaluations, homework and test results, student office visits, and senior exit interviews. Each of these methods has weaknesses if the primary objective is curriculum improvement. The new Accreditation Board for Engineering and Technology (ABET) Engineering Criteria 2000 (EC-2000) accreditation process requires new methods to allow for continuous program improvement. This paper discusses the six-week miniproject for senior students in the Electrical and Computer Engineering program at Bradley University. Use of the miniproject to steer the curriculum design content has been in place for eleven years. The evaluation results have been used successfully to implement course, laboratory, and curriculum modifications. The paper discusses the project, its costs, evaluation procedures, curriculum modifications and improvements, and use of the project in the EC-2000 accreditation process.     

Low-Temperature Oxygen Trap for Maintaining Strict Anoxic Conditions

A low-temperature O2 trap was designed in order to achieve strict anoxic conditions. The work was motivated by observation of slow oxidation of Fe(II) in an anaerobic chamber, leading to an estimated 3.8×10?7?atm O2 (well below the O2 monitor detection limit) despite recirculation of the N2:H2 atmosphere across a Pd catalyst. Very low O2 activity inside an “anaerobic” chamber can result in erroneous conclusions regarding oxidation-reduction reactivities in anoxic environments. The O2 trap consisted of two sequential barrier suspensions with 93.2?mM Fe(III) as ferric hydroxide, 0.90?mM FeCl2, and pH 8.1. The partial pressure of O2 was estimated to be less than 7.5×10?9?atm?O2 when reactors were attached to the traps, based on no observed oxidation of Fe(II).