bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of Low Molecular Weight Polylactic Acid
Authors: Proikakis C. S. , Tarantili P. A. , Andreopoulos A. G.
Published: July 2008

The polymerization of (D, L)-lactic acid in the absence of catalysts was studied. Azeotropic distillation using xylene, gave poly(lactic acid) with very low molecular weight, which however, was further increased by post-curing in an air oven. Moreover degradation phenomena and residual xylene were observed, with this procedure. Polycondensation of lactic acid at temperatures up to 180 C under vacuum, resulted in fast reaction with poor control and the products are still characterized by low molecular weight. When the reaction was run at 220 C in inert atmosphere, amorphous poly(lactic acid) was obtained with molecular weight exceeding 3000. The product was found pure, since it is free from solvents, catalysts and monomer. Also, no evidence of thermal degradation was observed. The above characteristics are well acceptable design aspects for biomedical uses.
New Ionic Polymer: Synthesis and Properties of “Zinc Sulfonated Natural Rubber”
Authors: Xavier Thommachan , Samuel Jacob , Manjooran K. B. , Kurian T.
Published: July 2008

Zinc sulfonated natural rubbers having different sulfonate contents were synthesized by the reaction of natural rubber with acetyl sulfate, followed by the neutralization of the resultant polymeric sulfonic acid with zinc acetate. The sample notation used for the ionomer is x y M-SNR, where x y is the degree of sulfonation expressed as meq/100 gm rubber, M is the neutralizing metal ion and SNR shows sulfonated natural rubber [Weiss, R.A., Fitzgerald, J.J. and Kim, D. (1991). Macromolecules, 1064: 24]. The modified samples of natural rubber were characterized using spectroscopic techniques such as X-ray Fluorescence Spectroscopy (XRFS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICPAES), Fourier Transform Infrared Spectroscopy (FTIR), Fourier Transform Nuclear Magnetic Resonance Spectroscopy (FTNMR), and by the evaluation of mechanical properties. The results show that the incorporation of sulfonate groups into NR improved its physical properties drastically. At a sulfonate level of 24.6 meq/100 g rubber, the tensile strength of the modified rubber incredibly increased to 13 MPa compared to the tensile strength of 0.36 MPa shown by unvulcanized base natural rubber. The Zn-SNR thus synthesized could be reprocessed at 150 C without sacrificing much of its tensile strength.
Polyether Derivatives of β-Naphthalene Sulfonate Polymer
Authors: Shendy Samy , Vickers Tom , Lu Runhai
Published: July 2008

This paper describes the synthesis and characterization of β-naphthalene sulfonate formaldehyde condensate (BNS) polymers grafted with pendant polyether molecules. For over 40 years, BNS have been considered as commercially useful material in the area of construction. It is added to concrete or mortar to give the concrete better properties either when fluid or plastic. It gives an adequate workability without the addition of extra water. BNS allow a large reduction of water content without affecting the workability of concrete as an example. Finally, the addition of BNS leads to simultaneous increase in both strength and workability without adding extra cost.
Compatibilization of PP/EPDM Blends via a Hexa Functional Coupling Agent and Peroxide During Reactive Extrusion
Authors: Ludwig Kristine N. , Moore Robert B.
Published: July 2008

Isotactic polypropylene (PP) and ethylene-propylene-methylene-norbornene terpolymer (EPDM) were blended in a counter-rotating twin screw extruder in the presence of a peroxide initiator and a new multifunctional coupling agent (hexa(allylamino)cyclotriphosphonitrile (HAP)). The effects of free radical coupling reactions on the mechanical properties and morphologies of the resultant blends were evaluated. Blends that included both HAP and peroxide displayed an increase in low temperature impact strength. Tapping-mode atomic force microscopy(AFM) of the alloys revealed enhanced dispersion of EPDM within the PP matrix when compared to the base blends.
Studies on Acrylonitrile Butadiene Rubber - Short Nylon Fiber Composites
Authors: Sreeja T. D. , Kutty S. K.N.
Published: July 2008

Acrylonitrile butadiene rubber (NBR) matrix was reinforced with different levels of short nylon fiber loading. Cure characteristics and mechanical properties of composites in longitudinal and transverse directions have been studied. Cure time was reduced while process ability, as indicated by the minimum torque, was marginally reduced with increase in fiber loading. Tensile and tear properties improved with fiber concentration and the values were higher in longitudinal direction of fiber orientation. Abrasion resistance, resilience and compression set were increased in presence of fibers. Elongation at break values showed a drastic drop on introduction of fibers. Heat build up was higher for composites.
Elastic-Plastic Stress Analysis of Composite Beams Loaded by Bending Moment
Authors: Sayman Onur , Uyaner Mesut , Daghan Behçet
Published: July 2008

An elastic-plastic stress analysis is carried out in a thermoplastic composite cantilever beam loaded by a bending moment at the free end. The orientation angle is chosen as 0°, 15°, 30° and 45°. An analytical solution is performed for satisfying both the governing differential equation in the plane stress case and boundary conditions for small plastic deformations. The solution is carried out under the assumption of the Bernoulli-Navier hypotheses. It is found that the intensity of the residual stress component σ x is maximum at the upper and lower surfaces. The beam material is assumed to be strain-hardening. The Tsai-Hill theory is used as a yield criterion. The displacement components are found in the elastic region.
Novel Eco-Friendly Biocomposites: Biofiber Reinforced Biodegradable Polyester Amide Composites—Fabrication and Properties Evaluation
Authors: Mishra S. , Tripathy S. S. , Misra M. , Mohanty A. K. , Nayak S. K.
Published: July 2008

Lignocellulosic natural fibers like sisal and pineapple leaf fiber (PALF) can be incorporated in polymers based on biodegradable polyester amide matrix, BAK 1095 for achieving desired properties and texture in the resulting biocomposites. But high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix led to debonding with age. In order to improve the above qualities, various surface treatments of sisal fiber like mercerization, cyanoethylation, acetylation, bleaching and vinyl monomer (acrylonitrile) grafting are carried out which results in improved mechanical performance of sisal-BAK composites. Mechanical properties like tensile and flexural strength are optimum at a fiber loading of 50 wt%. Among all modifications, alkali treatment and acetylation result in improved properties of the composites. Alkali treated sisal composite shows about 20% increase in tensile strength and acetylated sisal composite shows about 14% increase in flexural strength compared to the control, i.e., untreated sisal based biocomposites. From the biodegradation study, we find that after 60 days of soil burial about 1% weight loss is observed for BAK whereas acetylated sisal-BAK composite shows maximum weight loss (22%). It also shows maximum decrease in flexural strength (47%) after 15 days of sisal burial. A comparative account of properties of PALF-BAK and sisal-BAK biocomposites is also given. Scanning electron microscopic studies were carried out for better understanding of fiber-matrix adhesion in biocomposites.
Synthesis and Properties of Poly[N-(2-Hydroxypropyl) Methacrylamide] Conjugates of Superoxide Dismutase
Authors: šure Vladimír , Etrych Tomáš , Ulbrich Karel , Hirano Takashi , Kondo Tadashi , Todoroki Takeshi , Jelínková Markéta , Říhová Blanka
Published: July 2008

The synthesis of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers and semi-telechelic polymers (PHPMA) conjugates superoxide dismutase (SOD) is described. The polymer was conjugated with SOD by means ofnondegradable or degradable oligopeptide spacers randomly distributed along the polymer backbone. A second type ofconjugation, to a semi-telechelic polymer, poly(HPMA), (PHPMA) containing reactive chain end groups, with the SOD amino groups formed star structures. Physicochemical properties of the conjugates, such as temperature stability and stability to oxidation with hydrogen peroxide, were studied and compared to native SOD; an increase in temperature stability by the conjugates and an increase in stability towards oxidation with hydrogen peroxide was observed. The in vivo biological evaluation of PHPMA–SOD conjugates showed a significant decrease in immunogenicity compared to free SOD. A preliminary in vivo study of ischemic/reperfusion injury, revealed significantly more pronounced protective effects by PHPMA–SOD conjugates in comparison with the free SOD.
Preparation of Surface-Engineered Elastin/Lamin Nerve Guide Tubes of Poly(Lactic Acid)/Poly(Ethylene Vinyl Acetate)
Authors: Chandy Thomas , Rao Gundu H.R.
Published: July 2008

In this study, a spray coating technique was used to prepare poly(lactic acid) (PLA) tubes. To improve the flexibility of these devices, an elastomeric polymer, poly(ethylene vinyl acetate) (PEVAc), was added to the PLA. The PLA/PEVAc tubes were further surface modified with elastin and laminin via carbodiimide and glutaraldehyde treatment. This study evaluated the surface graft matrix components (elastin and laminin) on PLA/PEVAc tubes as a method for regenerating biointeractive materials for nerve growth and tissue engineering.
Microbiological Interaction and Diffusion Properties of Hydrophilic and Hydrophobic PU Membranes
Authors: Pulat Mehlika , Akdoğan Ayten , Özkan Semiha
Published: July 2008

In this study, the diffusion characteristics of Diclofenac-Na through hydrophobic and hydrophilic polyurethane (PU) based membranes areinvestigated. Hydrophilic polymers are obtained via graft copolymerization of PU with acrylic acid (AA) and crotonic acid (CA). The membranes are prepared by solvent-casting method and characterized by FTIR spectra and SEM analysis. The diffusion measurements are performed using a diffusion cell during 10 h at 37 °C. Permeability coefficients calculated from diffusion experiments are found to be approximately three times higher in hydrophilic membrane than hydrophobic PU membrane. The adherence of Escherichia coli (E. coli) and Staphylococcusaureus (S. aureus) onto the membranes at 37 °C were also investigated. It is determined that the microorganisms didn’t adhere onto the membranes compared by control suspension.
The Telescoping Suture – Part II: A Novel Method to Improve the Mechanical Behavior of a New Biomaterial: Ostrich Pericardium
Authors: Páez J. M. García , Herrero E. Jorge , Rocha A. , Martín-Maestro M. , Castillo-Olivares J. L. , Millaní I. , Sanmartín A. Carrera , Cordón A.
Published: July 2008

Ostrich pericardium, sutured using a telescoping or overlapping technique, was studied to determine its mechanical behavior. From each of 12 pericardial sacs, four contiguous strips were cut longitudinally, from root to apex, and another four contiguous strips were cut in transverse direction. One of the strips in each set of four was used as an unsutured control and the remaining three were sutured by overlapping 0.5 cm of the tissue and sewing with Gore-tex, Prolene or Pronova. These 96 samples were then subjected to tensile testing along their major axes until rupture. The tensile stresses recorded in the suture materials at the moment tears appeared in the pericardium rangedbetween 55.99 MPa and 70.23 MPa for Gore-tex in samples cut in the two directions. Shear stress became ostensible at 56 MPa, with clearly evident tears. However, microfracture of the collagen fibers must be produced at much lower stress levels. The comparison of the resistance in kilograms (machine-imposed), without taking into account the sections in which the load was applied, demonstrated only a slight loss of load when the telescoping suture was employed in ostrich pericardium samples. Ostrich pericardium may continue to be an alternative biological material for the construction of heart valve leaflets.
Evaluation of Electrostatically Endothelial Cell Seeded Expanded Polytetrafluoroethylene Grafts in a Canine Femoral Artery Model
Authors: Fields Charles , Cassano Anthony , Makhoul Raymond G. , Allen Cynthia , Sims Rick , Bulgrin Jeffrey , Meyer Andrew , Bowlin Gary L. , Rittgers Stanley E.
Published: July 2008

(1) Purpose: The purpose of this study was to evaluate the extent (luminal coverage) of the endothelial cell (EC) lining/neointimal development and the thromboresistance of electrostatically EC seeded small diameter e-PTFE vascular grafts.

(2) Methods: This evaluation consisted of harvesting autologous, canine jugular vein ECs, electrostatically EC seeding the e-PTFE grafts (4 mm GORE-TEX,® Length = 6 cm), implanting the grafts in a canine femoral artery model for six weeks, and excising the graft for histological and scanning electron microscopy evaluations.

(3) Results: The results of the histological evaluation (mid-graft region only) indicated that the electrostatic EC seeding significantly affected neointimal development (p<0.01) and the degree of thrombus formation (p<0.001) within the EC seeded grafts versus the untreated control grafts. Scanning electron microscopy examination demonstrated a mature, confluent endothelium with a “cobblestone” appearance on the EC seeded graft luminal surface. The control grafts demonstrated an equal distribution of SMCs through the graft wall while the electrostatically EC seeded graft sections exhibited an uneven SMC cellular distribution which was skewed toward the graft luminal surface.

(4) Conclusions: The presence of electrostatic EC seeding significantly (p<0.01) enhanced the development of a neointima and reduced the incidence of thrombosis in e-PTFE grafts implanted in a canine femoral artery model. Results of the mid-graft SMC migration measurements indicate that the electrostatic EC seeding had a significant (p<0.001) impact on the acute healing of the standard wall e-PTFE vascular graft specimens.
A Fuzzy Logic System for Ground Based Structural Health Monitoring of a Helicopter Rotor Using Modal Data
Authors: Ganguli Ranjan
Published: July 2008

A fuzzy logic system (FLS) is developed for ground based health monitoring of a helicopter rotor blade. Structural damage is modeled as a loss of stiffness at the damaged location that can result from delamination. Composite materials, which are widely used for fabricating rotor blades, are susceptible to such delaminations from barely visible impact damage. The rotor blade is modeled as an elastic beam undergoing transverse (flap) and in-plane (lag) bending, axial and torsion deformations. A finite element model of the rotor blade is used to calculate the change in blade frequencies (both rotating and nonrotating) because of structural damage. The measurements used for health monitoring are the first four flap (transverse bending) frequencies of the rotor blade. The measurement deviations due to damage are then fuzzified and mapped to a set of faults using a fuzzy logic system. The output faults of the fuzzy logic system are four levels of damage (undamaged, slight, moderate and severe) at five locations along the blade (root, inboard, center, outboard, tip). Numerical results with noisy data show that the FLS detects damage with an accuracy of 100% for noise levels below 15% when nonrotating frequencies are used. The FLS also correctly classifies the “undamaged” condition up to noise levels of 30% thereby reducing the possibility of false alarms, a key problem for diagnostics systems. The fuzzy logic approach is thus able to extract maximum information from very limited and uncertain data. Using rotating frequencies lowers the success rate for small damage because the centrifugal stiffening caused by rotation counters the stiffness reduction caused by structural damage. The fuzzy logic system in this study is proposed as an information-processing tool to help the maintenance engineer by locating the damage area roughly but accurately for further nondestructive inspections.
Comparative Analysis of the Time Response of Electrorheological and Magnetorheological Dampers Using Nondimensional Parameters
Authors: Choi Young-Tai , Wereley Norman M.
Published: July 2008

Electrorheological (ER) and magnetorheological (MR) fluids show similar field-dependent rheological characteristics from a bulk fluid perspective. However, the implementation of ER and MR fluids in devices may require different strategies because of the inherent properties of ER and MR fluids such as density, viscosity and the magnitude of the yield stress. Therefore, in this study, we explore the characteristics of ER and MR fluid-based systems on the basis of dynamic range and time response in order to comprehensively understand each system. In doing so, a nondimensional analysis, based on parallel plate geometry, is used to characterize the field-dependent properties of ER and MR fluid-based dampers. Experimental tests are conducted for ER and MR dampers in order to validate our analysis.
Semiactive Vibration Control of a Smart Seat with an MR Fluid Damper Considering its Time Delay
Authors: Park Chanho , Jeon Doyoung
Published: July 2008

The Lyapunov type robust control is applied to the semiactive vibration control of a controllable seat system to accommodate the modelling uncertainty of system and time delay of the damper. The seat system has a flexible mechanism of a spring and MR fluid damper between a seat cushion and base. Simulation results show that the robust control considering the time delay of the damper suppresses the seat vibration effectively.
Piezoresistive Cement-Based Materials for Strain Sensing
Authors: Chung D. D. L.
Published: July 2008

Cement-based materials that exhibit piezoresistivity with sufficient magnitude and reversibility contain electrically conductive fibers. The phenomenon allows the materials to sense their own strain. The fibers are preferably discontinuous. Carbon fibers (15 mm diameter) are most effective. Steel fibers (8 mm diameter) are less effective. Carbon filaments (0.1 mm diameter) are ineffective. The piezoresistive behavior, mechanism and materials are reviewed, including cement-based materials with continuous and discontinuous fibers.
Damage Mechanics Approach to Material-Dependency of Fracture Toughness in Aluminum Alloys
Authors: Tohgo Keiichiro , Mochizuki Kazuma
Published: July 2008

Mixed-mode elastic-plastic fracture toughness in aluminum alloys,i.e., heat-treatable and non-heat-treatable alloys, depends on the hardening mechanism. Present investigation have been carried out to clarify the material dependency of the fracture toughness in aluminum alloys. Two kinds of alloys were regarded as particle reinforced composites which contain inclusions and dispersoids in different matrices. The matrix in the non-heat-treatable alloy has low yield stress and high strain hardening, while the matrix in the heat-treatable alloy has high yield stress and low strain hardening because it is hardened by shearable precipitates. Elastic-plastic analyses of mode I and mode II cracks were conducted for two alloys using finite element method based on Tohgo–Chou–Weng’s constitutive relation of particle-reinforced composites which describes the plasticity of the matrix and the debonding damage between the particles and matrix. From the numerical results for plastic zone and damage evolution around a crack tip, it is qualitatively explained that the heat-treatable alloy exhibits the crack initiation in brittle manner from mode I crack and in ductile manner from mode II crack, while in the non-heat-treatable alloy the crack initiation occurs in ductile manner from both cracks.
On the Damage Behavior of Fiber Reinforced Composite Materials
Authors: Zako Masaru , Uetsuji Yasutomo
Published: July 2008

Since fiber reinforced composite materials have been used in main parts of structures, an accurate evaluation of their mechanical characteristics becomes very important. Due to their anisotropic nature and complicated architecture, it is very difficult to reveal the damage mechanism of these materials from the results of mechanical tests. Therefore, there is always a big need to conduct reliable simulations and analytical evaluations. In this paper, the damage behavior of FRP is simulated by finite element analysis using an anisotropic damage model based on damage mechanics. The proposed procedure is applied to two examples; the finite element analysis aided AE damage simulation and the finite element analysis of microscopic damage propagation in woven fabric composite materials. Experimental tests in both cases have been conducted to evaluate the validity of the proposed method. It is recognized that there is a good agreement between the analytical and experimental results, and that the proposed simulation method is very useful for the evaluation of damage mechanism.
Non-Linear Behaviour of Foam Cores and Sandwich Materials, Part 2: Indentation and Three-Point Bending
Authors: Lolive Éric , Berthelot Jean-Marie
Published: July 2008

This paper validates and applies a modelling procedure for analysing the non-linear behaviour of structures made of foams or sandwich materials with foam cores, subjected to mechanical loading. Modelling considers the non-linear behaviour of foam cores and permits the investigation of the fracture processes induced in the foam cores, in the skin layers or at the interfaces between the foam cores and the skins. Results deduced from the modelling procedure are compared with the experimental results obtained first in the case of indentation tests performed on foams and sandwich materials with foam cores and next in the case of foam sandwich materials subjected to three-point bending tests.
Innovative Polytrimethylene Terephthalate (Ptt) Polymers for Technical Nonwovens
Authors: Zhang Dong , Sun Christine , Beard John , Zhao Weili , Carson Ian , Hwo Charles
Published: July 2008

PTT (polytrimethylene terephthalate) (PTT) based meltblown and spunbonded webs have been produced by using Reicofil® Bi-Component Meltblown Line at TANDEC at the University of Tennessee and Reicofil® 3 Spunbonding system at Reifenhauser, Germany. The processability of meltblown and spunbonding in a wide range of operating windows was extensively investigated. The produced webs were characterized to optimize this process. It was found that the PTT grade studied is quite suitable for the meltblown and spunbonding process. The PTT/PP based bico meltblown webs showed enhanced barrier properties and heat resistance and the PTT spunbonded nonwovens showed advanced drapability and elastic recovery. Staple PTT fibers were also made into nonwovens using hydroentangling, thermobonding and needlepunching. Properties of these nonwovens were studied.
Development of Innovative Cotton-Surfaced Nonwoven Laminates
Authors: Sun Christine (Qin) , Zhang Dong , Wadsworth Larry C. , McLean Mac
Published: July 2008

Cotton-based nonwovens have been developed at Textiles and Nonwovens Development Center (TANDEC), The University of Tennessee, with the cotton fibers on the surface or in the core layer laminated with meltblown (MB) and/or spunbonded (SB) webs. Both Cotton-Surfaced Nonwovens (CSN) and Cotton-Core Nonwovens (CCN) have excellent soft hand, breathability, absorbency, and tensile properties making them ideal for many medical applications such as isolation gowns, hospital drapes and gowns, shoe covers, head covers, underwear, pillowcases, diaper components (acquisition, core, back sheet), feminine hygiene pads, baby wipes, etc. In this paper, the processes to produce these cotton-surfaced nonwovens will be presented, including as-bonded, heat-stretched CSN fabrics, and foam-finished CSN nonwovens.
Energy and Water Savings in the Textile Industry
Authors: Hall David M.
Published: July 2008

A unique water treatment system that alters the electro-chemistry of the managed water allows for a modification of the physical characteristics of cooling tower make up water that increases the solids content and certain other ions in the water. The result is a system that controls bacteria and fungi, eliminates bleed/blow down, eliminates corrosion and pitting, as well as scale through the use of Magnetic Field Generators that are a part of the system. The process continuously removes and filters solids, scale, and other debris from the system. The results of a study employing this process for three textile mills in Alabama are provided.
ESEM Study of Wetting of Untreated and Plasma Treated Polypropylene Fibers
Authors: Wei Q. F. , Mather R. R. , Fotheringham A. F. , Yang R. D.
Published: July 2008

Polypropylene (PP) fibers have been increasingly used in the technical textile industry for a variety of applications. Wetting behavior of PP fibers is of importance in these applications. The wetting behavior of the untreated and oxygen plasma treated polypropylene fibers was studied by the environmental scanning electron microscope (ESEM) in this work. Water droplets were formed on the cooled fibers by directly condensing water from the vapor phase. This was achieved by slowly increasing the vapor pressure inside the chamber towards the dew point for water at the appropriate specimen temperature. By this method small droplets in the micron range were condensed onto fiber surfaces. Contact angles of water on fiber surfaces were measured from the ESEM micrographs. The investigations have shown that the plasma treatment significantly altered the surface wettability of polypropylene fibers and that the ESEM provides a new approach to wetting and contact angle of fibers on the micron scale.
Polyacrylamide Based Breathable Coating for Cotton Fabric
Authors: Save Ninad S. , Jassal Manjeet , Agrawal Ashwini K.
Published: July 2008

Breathable coatings based on polyacrylamide on cotton fabrics have been developed. The coatings show high water vapor permeability, while providing desirable protection against air and liquid water-penetration. These polyacrylamide based coatings were obtained by coating the fabric with polyacrylamide solution (4%), containing citric acid as a crosslinker (5–50 mol%), and sodium hypophosphite (0.3%) as a catalyst, followed by drying at 90 C and curing at 150 C. The curing reaction leads to formation of crosslinks among the polymer chains as well as between the polymer and the cotton fabric. The integrity of the crosslinked polyacrylamide coating was observed to be good. The resistance, to hydrostatic head for double and triple-coated samples, with cross-linker concentration of 50 and 20 mol% was found to be in the range of 800–1280 mm, while the air-permeability values reduced drastically by two orders of magnitude, compared to the control fabric. The water vapor transmission rate (WVTR) values for these samples were found to be excellent with only 5–23% reduction compared to the values shown by control cotton fabric. The mechanism of the reaction leading to the formation of crosslinks has been evaluated using FTIR and NMR spectroscopy.
Specific Damping Capacity of Multiphase Unidirectional Hybrid Fiber Composites
Authors: Baburaj Vijayan , Matsuzaki Yuji , Nae Florin Andrei , Ikeda Tadashige
Published: July 2008

Modeling and analysis on the specific damping capacity (SDC) of a unidirectional hybrid fiber composite lamina have been presented in this paper. In an attempt to refine the SDC analysis for the case of hybrid composites a new unit cell has been identified. Idealization of the proposed unit cell introduces a fiber-matrix interphase into the hybrid composite damping model. Explicit lamina level SDC equations are derived using the strain energy method. The validity and the advantages of the present method have also been demonstrated by performing numerical simulations for conventional as well as shape memory alloy (SMA) hybrid fiber composites.
Experimental Research on the Blown Film Extrusion Process of Polyethylene
Authors: Sikora Janusz W.
Published: July 2008

Experimental studies of the blown film extrusion process presented in this paper aim at examining the influence of selected properties of constructional elements of intensive shearing and mixing on the characteristic of this process. The analysis concerned especially the influence of the thickness of the research gap between the inner surface of extruder barrel and the cylindrical surface of the intensive shearing ring placed in the screw’s metering section. Dependences of polymer mass flow rate, polymer head pressure, specific energy consumption of the extruder drive system and the component of extruder energy efficiency derived from its drive system on the frequency of screw rotation at different thickness of the research gap were presented.
Hydrolysis of Chitosan, Chitosan-Polyoxyethylene and Chitosan-Poly(2-acryloylamido-2-methylpropanesulfonic acid) by a Crude Enzyme Complex from Trichoderma viride
Authors: Stoilova O. , Koseva N. , Petrova Ts. , Manolova N. , Rashkov I. , Naydenov M.
Published: July 2008

The degradation of chitosan using a crude enzyme complex from the soil fungus Trichoderma viride was examined in terms of temperature, pH, enzyme activity and the presence of a polymer partner. It was found that chitosan hydrolysis is not suppressed by combining it with polyoxyethylene or poly(2-acryloylamido-2-methylpropanesulfonic acid). The results on Trichoderma viride immobilized on beads imply that chitosan, as well as its polymer complexes are appropriate carriers for development of ecologically safe phytosanitary preparations.
Isolation Design for Fully Flexible Systems
Authors: Sciulli Dino , Inman Daniel J.
Published: July 2008

It is commonly suggested that vibration isolators should be designed with a low-frequency mount, that is, the isolator frequency is much less than the first mode of the system being isolated. This is a direct result of the single-degree-of-freedom (SDOF) isolator model which states that the best performing isolator is the one that has the lowest natural frequency. When flexibility is included in the isolator design, the low-frequency mount design still performs best in an overall sense. However, with system flexibility being modeled, the isolator can now be designed between the modes of the flexible system. These types of isolator mounts tend to have a coupling effect, that is, the frequencies around the isolator mount have such a strong interaction between each other that when isolator damping is present, multiple system modes are attenuated. Therefore, this paper fully explores the choice of isolator mount frequency and isolator placement for fully flexible systems. Results show that a low-frequency mount design considering base and equipment flexibility, will have the first natural frequency shift by as much as 15.6%. For a mid-frequency mount design, the shift of the first three modes can be as high as 34.9%, 26.6% and 11.3%, respectively. Also, when base and system flexibility is considered, isolator placement becomes a critical issue. There can be as much as 16% difference in the first mode for a low-frequency mount design and as high as 25% difference for a mid-frequency mount design.
Bridging the Modulus Gap between LLDPE and HDPE
Authors: Williams Kelly L.
Published: July 2008

Developing blown film resins for the production of films that exhibit the toughness properties of linear low density polyethylene (LLDPE) with the stiffness and tensile characteristics of high density polyethylene (HDPE) has historically been difficult to achieve for both resin producers and film converters. Resin producers have attempted to push the density higher for LLDPE film resins and lower for HDPE film resins. Separately, film producers are continuously searching for the same hybrid film through blending low (LDPE), linear low (LLDPE), medium (MDPE) and high-density (HDPE) polyethylenes. Producing successful film blends for heavy-duty applications with densities over 0.918 g/cm3 usually results in a high performance LLDPE film resin being blended with low levels of a MDPE or HDPE. As the level of MDPE or HDPE increases, loss of critical toughness properties such as machine direction tear (MD tear) and dart impact strength is observed.

There now exists a novel method of producing films that possess a full density range between 0.918 g/cm3 and 0.938 g/cm3. This approach is based on the utilization of a new family of high molecular weight medium density polyethylene (HMW-MDPE) film resins. By blending an HMW-MDPE with a resin density of 0.938 g/cm3 with high performance LLDPE film resins, films can be fabricated over a wide range of densities without the loss of tear and impact properties. These blends can be produced at thin or thick gauges on either high stalk or conventional blown film equipment.
Optimal Dynamic Response Control of Adaptive Thin-Walled Cantilevers Carrying Heavy Stores and Exposed to Blast Pulses
Authors: Na Sungsoo , Librescu Liviu
Published: July 2008

The optimal dynamic response control of adaptive thin-walled beam cantilevers carrying externally mounted stores and exposed to blast pulses is investigated. The structure under consideration is modeled as a thin-walled beam of closed cross-section contour, encompassing a number of non-classical features such as transverse shear, secondary warping, and anisotropy of the constituent materials. The structure can carry along its span heavy concentrated masses and/or tip stores. The vibration control is achieved via the use of actuating and sensing capabilities provided by piezoelectric devices which are bonded or embedded into the host structure. The cases of piezoactuators spread over the entire span of the structure, or in the form of a patch are considered, and issues related to the influence of patch location and size upon the vibration control efficiency are highlighted. Other issues related to the minimization of the required input power and of that generated by the inclusion/discard in the quadratic performance index of time-dependent external excitations are also addressed.
Blending of High-Performance LLDPEs with Butene-LLDPEs and LDPEs
Authors: Mavridis Harry
Published: July 2008

Several high-performance LLDPE resins for film applications have been developed in the past few years through Advanced Ziegler–Natta or Single-Site catalysts. These new resins significantly improve the film properties of conventional Ziegler–Natta resins, but they are generally more costly and/or more difficult to process. A relatively simple strategy for addressing the cost and processability issues is via post-reactor blending, either with butene-LLDPEs in order to reduce cost, or with LDPEs in order to improve processability. Blending of high-performance resins has a generally detrimental effect on film strength properties, although there are exceptions in certain compositions. Viability of a certain blend composition thus hinges on a cost versus performance evaluation of the properties of interest. The present work focuses on the performance aspect, through a study of the effect of blending butene-LLDPEs and LDPEs on the optical and mechanical properties of Advanced Ziegler–Natta and metallocene-LLDPEs.
Interactions of Magnetic Field and the Magnetic Fluid Surface
Authors: Sudo S. , Nishiyama H. , Katagiri K. , Tani J.
Published: July 2008

This paper is concerned with the interaction between the applied magnetic field and the magnetic fluid surface. Liquid responses of magnetic fluids under the magnetic and vibrating fields were investigated. Experiments were performed on a vibration-testing system which provided lateral and longitudinal excitation. The effect of the magnetic field gradient on liquid surface motion in an open circular cylindrical tank was noted. Details of surface responses of a magnetic fluid in the cylindrical container excited longitudinally under an applied magnetic field were revealed. Some similarities and differences between single magnetic spike oscillation and the symmetric free surface mode (0, 1) of magnetic liquid sloshing in the presence of a magnetic field were investigated. It was found that the elongation of the symmetric free surface mode (0, 1) and single magnetic spike were based on the same mechanism. The formation and the disappearance of magnetic drops formed by surface disintegration in the cylindrical container subject to horizontal vibration were also investigated. It was observed that the number of floating drops induced by vibrating the cylindrical container laterally with the natural frequency of the fluid-container system, decreased greatly with the magnetic field intensity.
The Use of Piezoceramic Transducers for Smart Structural Testing
Authors: Wang Bor-Tsuen , Chen Rong-Liang
Published: July 2008

This paper presents the use of piezoceramic transducers, Lead Zirconia Titanate (PZT) actuators and Polyvinylidene Fluoride (PVDF) sensors, for experimental modal testing of a simply supported plate. A series of rectangular-shaped PVDF films are evenly distributed over the plate and act as the sensing devices instead of traditional acceleration sensors. Pairs of rectangular PZT patches are bounded to opposite sides of the plate to form actuators and when they are excited by 180° out-of-phase stimulation, they will cause pure bending. The theoretical formulation of frequency response functions (FRFs) of the piezoceramic transducers is developed. The mode shape functions of the PZT actuator and the PVDF sensor are identified, respectively. Experiments are performed to obtain a column of FRF matrix. The structural modal parameters, including natural frequencies, modal damping ratios and mode shapes, can then be extracted by a modal parameter extraction method. Results show the modal parameters can be properly obtained and physically interpreted. This paper presents the concepts of smart structural testing (SST) with the use of piezoceramic transducers and leads to the applications of smart structures to health monitoring of structural systems.
Adaptive Neurocontrol of Simulated Rotor Vibrations Using Trailing Edge Flaps
Authors: Spencer Michael G. , Sanner Robert M. , Chopra Inderjit
Published: July 2008

Smart structure activated trailing edge flaps are capable of actively altering the aerodynamic loads on rotor blades. Coupled with a suitable feedback control law, such actuators could potentially be used to counter the vibrations induced by periodic aerodynamic loading on the blades, without the bandwidth constraints and with a potential of lower weight penalties incurred by servo actuation methods. This paper explores new, robust individual blade control (IBC) methodologies for vibration suppression using a piezoactuated trailing edge flap. The controllers employ a single hidden layer neural network, learning in real time, to adaptively cancel the effects of periodic aerodynamic loads on the blades, greatly attenuating the resulting vibrations. Both collocated and noncollocated sensor/actuator pairs are considered. Proofs of the stability and convergence of the proposed neurocontrol strategies are provided, and numerical simulation results for a one-eighth Froude scale blade model are given which demonstrate that the controller can nearly eliminate the blade vibration arising from a wide variety of unknown, periodic disturbance sources.
Adaptive Imperfect Column with Piezoelectric Actuators
Authors: Alghamdi Abdulmalik A. A.
Published: July 2008

This paper discusses the stability of long imperfect adaptive (or smart) columns. The mechanics of a smart column having piezoelectric elements as active elements is introduced first. Then, the governing differential equation of the adaptive column is presented. A numerical example is given to show the capability of active piezo-ceramic elements in enhancing structural stability of long imperfect column. Obtained numerical results show improved stability performance of the adaptive column in comparison with the passive one. It is possible to straighten initially imperfected columns using surface attached active elements.
Origins of Activity Patterns in Self-Organizing Neuronal Networks in Vitro.
Authors: Gross Guenter W , Kowalski Jacek M.
Published: July 2008

Nerve cell ensembles growing in culture on microelectrode arrays allow long-term, multisite monitoring of spontaneous and evoked action potential (spike) activity. These ensembles generate complex spatio-temporal spike patterns and constitute evolving non-linear and non-station-ary dynamical systems. They provide effective platforms for observations of the "internal dynamics" of neuronal networks, especially pattern generation and the evolution of network organization. Nerves cells in cultures form many small neuronal clusters (termed nacelles) in which substantial membrane contact is achieved. We propose that such morphological clusters generate subthreshold interactions that can lead to noise-induced membrane potential oscillations with frequent ignition to spiking. Recruitment of several nacelles and dispersed neurons then leads to dynamically organized circuits capable of reliably generating and maintaining a specific burst pattern. The observed coexistence of different burst patterns suggests network substructures (circuits) with autonomous activity. Entrainment of all circuits to a global pattern is thought to represent a network "decision state" with automatic fault-tolerant output. Such phenomena suggest that not only the redundancy of connections but also the form of the message are important factors in the creation of fault-tolerance.
Optimal Placement of Passive Dampers on Seismic and Wind-Excited Buildings using Combinatorial Optimization
Authors: Agrawal A. K. , Yang J. N.
Published: July 2008

The performance of energy dissipative systems for the response reduction of complex civil engineering structures depends on their locations in the structure. In this paper, the optimal locations of energy dissipative systems have been investigated using combinatorial optimization based integer heuristic programming techniques. Three intelligent search algorithms, namely, sequential, Worst-Out-Best-In (WOBI) and Exhaustive Single Point Substitution (ESPS) search methods, have been used to determine optimal locations for different types of objective functions. The applications of the proposed approach for the determination of optimal locations have been demonstrated for three seismic-excited buildings and one wind-excited building. It is shown that the optimal locations obtained by minimizing the peak interstory drift of buildings depend on the specific design earthquake. The WOBI and ESPS methods have been found to be quite effective in improving the locations obtained by the sequential search method.
Vibration Suppression Via Smart Structures Across a Temperature Range
Authors: Hegewald Thomas , Inman Daniel J.
Published: July 2008

Many vibration suppression systems are required to function across a variety of different temperatures, yet most literature ignores the effects of temperature changes on the structure and on the closed loop response. This paper presents an experimental implementation of a vibration suppression system based on a piezoceramic actuator that effectively controls vibration of a clamped panel as it undergoes a variation in ambient temperature. The desire to reduce fatigue in aircraft panels motivates this experimental investigation and implementation.
Haem‐regulated eIF2α kinase is necessary for adaptive gene expression in erythroid precursors under the stress of iron deficiency
Authors: Liu Sijin , Bhattacharya Sanchita , Han Anping , Suragani Rajasekhar N. V. S. , Zhao Wanting , Fry Rebecca C. , Chen Jane‐Jane
Published: July 2008

Haem‐regulated eIF2α kinase (HRI) is essential for the regulation of globin gene translation and the survival of erythroid precursors in iron/haem deficiency. This study found that that in iron deficiency, fetal definitive erythropoiesis is inhibited at the basophilic erythroblast stage with increased proliferation and elevated apoptosis. This hallmark of ineffective erythropoiesis is more severe in HRI deficiency. Microarray gene profiling analysis showed that HRI was required for adaptive gene expression in erythroid precursors during chronic iron deficiency. The number of genes with expression affected more than twofold increased, from 213 in iron deficiency and 73 in HRI deficiency, to 3135 in combined iron and HRI deficiencies. Many of these genes are regulated by Gata1 and Fog1. We demonstrate for the first time that Gata1 expression in developing erythroid precursors is decreased in iron deficiency, and is decreased further in combined iron and HRI deficiencies. Additionally, Fog1 expression is decreased in combined deficiencies, but not in iron or HRI deficiency alone. Our results indicate that HRI confers adaptive gene expression in developing erythroblasts during iron deficiency through maintaining Gata1/Fog1 expression.
A population‐specific Mini‐Nutritional Assessment can effectively grade the nutritional status of stroke rehabilitation patients in Taiwan
Authors: Tsai Alan C , Shih Chi‐Ling
Published: July 2008

Aims and objectives.  To determine whether a modified version of the Mini‐Nutritional Assessment without body mass index could effectively assess the nutritional risk status of stroke rehabilitation patients in Taiwan.

Background.  The Mini‐Nutritional Assessment was developed on the basis of clinical data of Western populations. Although widely used, its application to assess stroke rehabilitation patients has been limited. Further, to get best results, population‐specific modifications to address anthropometric and lifestyle differences have been suggested, especially for non‐Caucasian populations.

Design.  The study assessed the nutritional status of stroke rehabilitation patients who enrolled in the Long‐term Care Service of Taipei. Strokes who were >40 years old, in the program for >1 month and cognitively able to answer the questions were recruited to participate in the study.

Methods.  An on‐site in‐person interview with structured questionnaire elicited information on personal data, disease history and healthcare use and answers to the Mini‐Mental State Examination, the Activities of Daily Living and the Mini‐Nutritional Assessment. Patient’s nutritional status was assessed with the Mini‐Nutritional Assessment in three versions: the original, population‐specific (MNA‐TI) and population‐specific, without body mass index (MNA‐TII).

Results.  The original Mini‐Nutritional Assessment rated 24% of patients malnourished and 57% at risk of malnutrition. Similar results, 14 and 64%, respectively, for MNA‐TI; and 19 and 57%, respectively, for MNA‐TII were observed.

Conclusion.  Both the original and the modified versions of the Mini‐Nutritional Assessment can effectively rate the nutritional risk status of stroke rehabilitation patients in Taiwan. Version MNA‐TII that adopted population‐specific anthropometric cut‐values but without body mass index can effectively predict the nutritional status of stroke patients.

Relevance to clinical practice.  The modified scale (MNA‐TII) can enhance the application of the tool and timely detection and intervention of undernutrition among stroke rehabilitation patients. It can also help to improve job efficiency of the primary care professionals.