STABILITY OF A PROPAGATING INTERPHASE BOUNDARY IN A THERMOPLASTIC MATERIAL

We study the morphological stability of a propagating planar interphase boundary in a thermoplastic material deformed in antiplane shear. The plane interphase boundary is found to be stable if σ₀/(₄ρcrpar;V₀ ²where c is the specific heat per unit uolume; p is the mass density; V₀is a proagation speed; and σ₀is a function of the material moduli and the state of deformation of the body.     

Pyroelectric Properties of PVDF:MWCNT Nanocomposite Film for Uncooled Infrared Detectors and Medical Applications

The biocompatible and flexible polyvinylidene fluoride (PVDF) has a number of interesting pyroelectric and piezoelectric properties with fast, dynamic response for use in touch/tactile sensors, infrared detectors and thermal vidicon/imaging devices. Pyroelectric multi-walled carbon nano-tubes:polyvinylidene fluoride nano-composite films were fabricated via the solution casting technique. The dielectric, pyroelectric and piezoelectric characteristics of composite films were measured. Using foregoing parameters, figures-of-merit for infrared detectors, and thermal-vidicons were calculated. The results indicated figures-of-merit of the composite film that were higher than pristine polyvinylidene fluoride film. The potential applications of composite films in medical devices are also discussed.     

Three-dimensional numerical simulation of the Kalthoff experiment

We use the finite element code DYNA3D to analyze large thermomechanical deformations of a prenotched plate impacted on the notched side by a cylindrical projectile moving parallel to the axis of the notch. Both the projectile and the plate are assumed to be made of the same thermally softening but strain and strain-rate hardening material. It is found that the maximum speed imparted to points of the plate on the impact surface equals nearly 90% of the projectile speed, and the rise time depends upon the quasistatic yield stress of the material. Whereas deformations on the midsurface of the plate closely resemble a plane strain state of deformation, those on the traction free front and back surfaces are quite different. Thus measurements made on these surfaces may not describe well the deformations occurring in the interior of the plate.     

Significant yield improvement in the stereoselective synthesis of allyl cyanides from Baylis–Hillman derivatives in aqueous medium under the influence of the phase-transfer catalyst

The nucleophilic reaction of NaCN with the acetyl derivative of Baylis–Hillman adducts in the presence of a phase-transfer catalyst in aqueous medium stereoselectively affords the corresponding allyl cyanides in a short period and excellent yields.     

Transformations in Sol-Gel Synthesized Nanoscale Hydroxyapatite Calcined Under Different Temperatures and Time Conditions

Nano-hydroxyapatite (HAP) has been synthesized using sol-gel technique. Calcium nitrate tetrahydrate and potassium dihydrogen phosphate were used as precursors for calcium and phosphorus, respectively. A detailed study on its transformation during calcination at two crucial temperatures has been undertaken. The synthesized nanopowder was calcined at 600 and 800?°C for different time periods. The results revealed that the obtained powders after calcining at 600 and 800?°C are composed of hydroxyapatite nanoparticles. The nano-HAP powders were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, thermal gravimetric analysis (TGA), and BET surface area analyzer techniques. The results indicate that crystallite size as well as crystallinity of synthesized HAP nanopowders increase with increase in calcination temperature as well as calcination time, but the effect of temperature is more prominent as compared to that of calcination time. TEM micrograph revealed the presence of majority of HAP powder particles as agglomerates and a few as individual particles. It also revealed that HAP produced after sintering at 600?°C is 26-45?nm in size, which is well in agreement with the crystallite size calculated using XRD data. TGA study showed the thermal stability of the as-synthesized nano-HAP powder. The BET surface area decreased with increase in calcination temperature and time. The results clearly demonstrate the significant role of calcination parameters on the characteristics of nano-HAP powders.     

Failure Analysis of Steam Turbine Rotor Disk

This article presents an investigation into causes of failure of rotor disk of an 8.25-MW capacity steam turbine, which failed catastrophically. Four pieces of the rotor disk detached from the tenth-stage disk of the turbine rotor during this failure. Visual inspection, chemical analysis, macro- and microscopic analysis of the failed rotor disk, analysis of the operational data, and the history of the rotor operation indicated that the failure could be attributed to stress concentrations at macropores and regions of segregation in the disk. Stress corrosion cracking (SCC) subsequently took place in the regions of stress concentration because the steam in the turbine contained chloride and potassium. The SCC produced a network of cracks associated with the macro- and microporosities. It was recommended that the disk fabrication processes ensure a high-quality microstructure and that operational monitoring of the composition of steam be initiated to ensure that the chlorides and potassium concentrations are maintained below a specified level.     

Pharmacokinetics and biodistribution of genetically-engineered antibodies

Monoclonal antibodies (MAbs), because of their inherent specificity, are ideal targeting agents. They can be used to deliver radionuclides, toxins or cytotoxic drugs to a specific tissue or malignant cell populations. Intact immunoglobulin (IgG) molecules have several practical limitations of their pharmacology; their relatively large size of approximately 150,000 daltons leads to a slow clearance from the blood pool and the body resulting in significant exposure to normal organs with limited quantities delivered to tumors. The IgG molecule shows a relatively poor diffusion from the vasculature into and through the tumor. Attempts to modify the pharmacology of the Ig molecule have classically involved the use of proteases to generate F(ab')2 and Fab' fragments with molecular weights of approximately 100,000 and 50,000 daltons, respectively. Fv fragments of IgG are one of the smallest size functional modules of antibodies that retain high affinity binding of an antigen. Their smaller size, approximately 25,000 daltons, enables better tumor penetration and makes them potentially more useful than a whole antibody molecule for clinical applications. Molecular cloning and expression of the variable region genes of IgG has greatly facilitated the generation of engineered antibodies. A single-chain Fv (scFv) recombinant protein, prepared by connecting genes encoding for heavy-chain and light-chain variable regions at the DNA level by an appropriate oligonucleotide linker, clears from the blood at much faster rate than intact IgG. The scFv fragment can retain an antigen-binding affinity similar to that of a monovalent Fab' fragment; this however, represents a relative decrease in binding affinity when compared to intact antibodies. The scFv with its faster clearance and lower affinity results in a lower percent-injected dose localizing in tumors when compared to the divalent IgG molecule. This may be adequate for imaging but probably not for therapy. The valency of the MAb fragment is critical for the functional affinity of an antibody to a cell surface or a polymeric antigen. In attempts to generate multivalent forms of scFv molecules, non-covalently linked scFv dimeric and trimeric molecules, disulfide linked dimeric scFvs, as well as covalently linked chimeric scFvs have been studied. These multivalent scFvs generally have a higher functional affinity than the monovalent form resulting in better in vivo targeting. Another way to alter the pharmacology of the scFvs is to modify its net charge. Charge-modified scFvs with desired isoelectric points (pI), have been prepared by inserting negatively charged amino acids on the template of the variable region genes. This can help to overcome undesirable elevations in renal uptake seen with most antibody fragments. In conclusion, genetic manipulations of the immunoglobulin molecules are effective means of altering stability, functional affinity, pharmacokinetics, and biodistribution of the antibodies required for the generation of the "magic bullet".     

Three-Dimensional transient heat conduction in a functionally graded thick plate with a higher-order plate theory and a meshless local Petrov-Galerkin method

We analyze transient heat conduction in a thick functionally graded plate by using a higher-order plate theory and a meshless local Petrov-Galerkin (MLPG) method. The temperature field is expanded in the thickness direction by using Legendre polynomials as basis functions. For temperature prescribed on one or both major surfaces of the plate, modified Lagrange polynomials are used as basis and additional terms are added to these expansions to exactly match the given temperatures. Partial differential equations for the evolution of the coefficients of the Legendre polynomials are reduced to a set of coupled ordinary differential equations (ODEs) in time by a MLPG method. The ODEs are integrated by the central-difference method. The time history of evolution of the temperature at the plate centroid and through-the-thickness distribution of the temperature computed with the fifth-order plate theory are found to agree very well with those obtained analytically.Acknowledgements This work was partially supported by the ONR grant N0014-98-1-0300 to Virginia Polytechnic Institute and State University with Dr. Y. D. S. Rajapakse as the cognizant Program Manager. L. F. Qian was also supported by the China Scholarship Council.     

Austempering and austempered ductile iron microstructure in copper alloyed ductile iron

The variation in the austempered microstructure, the volume fraction of retained austenite, X_λ, the average carbon content of retained austenite, C_λ, their product X_λC_λ and the size of bainitic ferrite needles with austempering temperature for 0.6% Cu alloyed ductile iron have been investigated for three austempering temperatures of 270, 330, and 380 °C for 60 min at each temperature after austenitization at 850 °C for 120 min. The austempering temperature not only affects the morphology of bainitic ferrite but also that of retained austenite. There is an increase in the amount of retained austenite, its carbon content, and size of bainitic ferrite needles with the rise in austempering temperature. The influence of austempering time on the structure has been studied on the samples austempered at 330 °C. The increase in the austempering time increases the amount of retained austenite and its carbon content, which ultimately reaches a plateau.