bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection and Genotyping of
Entamoeba histolytica
,
Entamoeba dispar
,
Giardia lamblia
, and
Cryptosporidium parvum
by Oligonucleotide Microarray
Authors: Wang Zheng , Vora Gary J. , Stenger David A.
Published: July 2004

Entamoeba histolytica
,
Giardia lamblia
, and
Cryptosporidium parvum
are the most frequently identified protozoan parasites causing waterborne disease outbreaks. The morbidity and mortality associated with these intestinal parasitic infections warrant the development of rapid and accurate detection and genotyping methods to aid public health efforts aimed at preventing and controlling outbreaks. In this study, we describe the development of an oligonucleotide microarray capable of detecting and discriminating between
E. histolytica
,
Entamoeba dispar
,
G. lamblia
assemblages A and B, and
C. parvum
types 1 and 2 in a single assay. Unique hybridization patterns for each selected protozoan were generated by amplifying six to eight diagnostic sequences/organism by multiplex PCR; fluorescent labeling of the amplicons via primer extension; and subsequent hybridization to a set of genus-, species-, and subtype-specific covalently immobilized oligonucleotide probes. The profile-based specificity of this methodology not only permitted for the unequivocal identification of the six targeted species and subtypes, but also demonstrated its potential in identifying related species such as
Cryptosporidium meleagridis
and
Cryptosporidium muris
. In addition, sensitivity assays demonstrated lower detection limits of five trophozoites of
G. lamblia
. Taken together, the specificity and sensitivity of the microarray-based approach suggest that this methodology may provide a promising tool to detect and genotype protozoa from clinical and environmental samples.
Use of Applied Biosystems 7900HT Sequence Detection System and Taqman Assay for Detection of Quinolone-Resistant
Neisseria gonorrhoeae
Authors: Giles Julie , Hardick Justin , Yuenger Jeffrey , Dan Michael , Reich Karl , Zenilman Jonathan
Published: July 2004

Mutations in quinolone resistance-determining regions (QRDRs) have been associated with quinolone-resistant
Neisseria gonorrhoeae
(QRNG). Since diagnostic nucleic acid amplification tests for gonococci are now in frequent use, molecular detection of QRNG could facilitate surveillance in the absence of culture. Here we describe a real-time molecular assay for detecting QRDR mutations in gonococci.
Identification of the Severe Acute Respiratory Syndrome Coronavirus by Simultaneous Multigene DNA Sequencing
Authors: Vinayagamoorthy T. , Mulatz Kirk , Hodkinson Roger
Published: July 2004

The recent severe acute respiratory syndrome (SARS) outbreak resulted in calls for an accurate diagnostic test that can be used not only for routine testing but also for generating nucleotide sequences to monitor the epidemic. Although the identity of the SARS coronavirus (SARS-CoV) genome was confirmed by DNA sequencing, it is impractical to sequence the entire 29-kb SARS-CoV genome on a routine basis. Therefore, alternative assay methods such as the enzyme-linked immunosorbent assay and PCR have been pursued for routine testing, primarily to resolve probable cases. We report here a modification of standard DNA sequencing technology for accurate identification of SARS-CoV in routine testing. Instead of requiring the sequencing of the whole SARS-CoV genome, our modification enables the simultaneous sequencing of three regions of the SARS-CoV genome, the spike protein-encoding gene (35 nucleotides), gene M (43 nucleotides), and gene N (45 nucleotides), in a single electropherogram. Comparing these nucleotide sequences to DNA databank entries (National Institutes of Health) conclusively identified them as SARS-CoV sequences.
A Novel Multiplex Real-Time PCR Assay for Rapid Typing of Major Staphylococcal Cassette Chromosome
mec
Elements
Authors: Francois Patrice , Renzi Gesuele , Pittet Didier , Bento Manuela , Lew Daniel , Harbarth Stephan , Vaudaux Pierre , Schrenzel Jacques
Published: July 2004

We describe a novel procedure for rapid typing of the staphylococcal cassette chromosome
mec
element, a molecular marker allowing discrimination between community- and hospital-acquired methicillin-resistant
Staphylococcus aureus
(MRSA) strains. Oligonucleotides targeting the recombinase genes were type specific and used to type a collection of 399 MRSA isolates recovered during patient screening at admission. This novel assay constitutes a valuable tool for evaluating the molecular epidemiology of MRSA and adjusting infection control strategies against MRSA.
Genotypic Profile of Human Herpesvirus 8 (Kaposi's Sarcoma-Associated Herpesvirus) in Urine
Authors: Beyari M. M. , Hodgson T. A. , Kondowe W. , Molyneux E. M. , Scully C. M. , Porter S. R. , Teo C. G.
Published: July 2004

Human herpesvirus 8 (HHV-8) open reading frame K1 sequences amplified from the urine of 5 of 78 (6.4%) infected people in Malawi were monotypic. In two people, urinary and oral sequences were genotypically different. Comprehensive evaluation of HHV-8 transmission may require characterization of HHV-8 shed both in urine and orally.
Genetic Relatedness and Quinolone Resistance of
Campylobacter jejuni
Strains Isolated in 2002 in Hong Kong
Authors: Chu Yiu-Wai , Chu Man-Yu , Luey Kit-Yee , Ngan Yin-Wa , Tsang Ka-Lok , Kam Kai-Man
Published: July 2004

Pulsed-field gel electrophoresis fingerprints of 98
Campylobacter jejuni
isolates from patients (85) and chicken carcasses (13) in Hong Kong in 2002 demonstrated high genetic diversity. The prevalence of quinolone resistance among the isolates was 85.9%, and replacement of the threonine-86 residue in the gyrase subunit A was the major resistance mechanism.
Direct Identification of
Mycobacterium haemophilum
in Skin Lesions of Immunocompromised Patients by PCR-Restriction Endonuclease Analysis
Authors: Wang S. X. , Sng L. H. , Leong H. N. , Tan B. H.
Published: July 2004

PCR-restriction endonuclease analysis (PRA) was used for direct identification of
Mycobacterium haemophilum
in clinical specimens from immunocompromised patients. PRA correctly identified
M. haemophilum
in four smear-positive specimens. Direct identification by PRA takes 2 to 3 working days compared to the 3 to 5 weeks required for culture isolation and identification by conventional methods.
Diagnostic Utility and Clinical Significance of Naso- and Oropharyngeal Samples Used in a PCR Assay To Diagnose
Mycoplasma pneumoniae
Infection in Children with Community-Acquired Pneumonia
Authors: Michelow Ian C. , Olsen Kurt , Lozano Juanita , Duffy Lynn B. , McCracken George H. , Hardy R. Doug
Published: July 2004

PCR assays of naso- and oropharyngeal samples among hospitalized children appear equally effective for the diagnosis of serologically confirmed community-acquired mycoplasmal pneumonia. However, the combination of results from both sites yields optimal sensitivity (57%), specificity (98%), and positive (92%) and negative (82%) predictive values when compared with
Mycoplasma pneumoniae
enzyme-linked immunosorbent assay.
First Comprehensively Documented Case of
Paracoccus yeei
Infection in a Human
Authors: Funke Guido , Frodl Reinhard , Sommer Hartmut
Published: July 2004

Paracoccus yeei
was isolated in pure culture from an aerobic blood culture and bulla fluid from a 67-year-old male. The biochemical identification scheme for this recently described species is outlined. Because of its reaction pattern it is not unlikely that
P. yeei
is underdiagnosed.
Glycolate and glyoxylate metabolism in HepG2 cells
Authors: Baker Paul R. S. , Cramer Scott D. , Kennedy Martha , Assimos Dean G. , Holmes Ross P.
Published: July 2004

Oxalate synthesis in human hepatocytes is not well defined despite the clinical significance of its overproduction in diseases such as the primary hyperoxalurias. To further define these steps, the metabolism to oxalate of the oxalate precursors glycolate and glyoxylate and the possible pathways involved were examined in HepG2 cells. These cells were found to contain oxalate, glyoxylate, and glycolate as intracellular metabolites and to excrete oxalate and glycolate into the medium. Glycolate was taken up more effectively by cells than glyoxylate, but glyoxylate was more efficiently converted to oxalate. Oxalate was formed from exogenous glycolate only when cells were exposed to high concentrations. Peroxisomes in HepG2 cells, in contrast to those in human hepatocytes, were not involved in glycolate metabolism. Incubations with purified lactate dehydrogenase suggested that this enzyme was responsible for the metabolism of glycolate to oxalate in HepG2 cells. The formation of 14C-labeled glycine from 14C-labeled glycolate was observed only when cell membranes were permeabilized with Triton X-100. These results imply that peroxisome permeability to glycolate is restricted in these cells. Mitochondria, which produce glyoxylate from hydroxyproline metabolism, contained both alanine:glyoxylate aminotransferase (AGT)2 and glyoxylate reductase activities, which can convert glyoxylate to glycine and glycolate, respectively. Expression of AGT2 mRNA in HepG2 cells was confirmed by RT-PCR. These results indicate that HepG2 cells will be useful in clarifying the nonperoxisomal metabolism associated with oxalate synthesis in human hepatocytes.
Electrophysiological Properties of Mouse Horizontal Cell GABAAReceptors
Authors: Feigenspan Andreas , Weiler Reto
Published: July 2004

GABA-induced currents have been characterized in isolated horizontal cells from lower vertebrates but not in mammalian horizontal cells. Therefore horizontal cells were isolated after enzymatical and mechanical dissociation of the adult mouse retina and visually identified. We recorded from horizontal cell bodies using the whole cell and outside-out configuration of the patch-clamp technique. Extracellular application of GABA induced inward currents carried by chloride ions. GABA-evoked currents were completely and reversibly blocked by the competitive GABAAreceptor antagonist bicuculline (IC50= 1.7 μM), indicating expression of GABAAbut not GABACreceptors. Their affinity for GABA was moderate (EC50= 30 μM), and the Hill coefficient was 1.3, corresponding to two GABA binding sites. GABA responses were partially reduced by picrotoxin with differential effects on peak and steady-state current values. Zinc blocked the GABA response with an IC50value of 7.3 μM in a noncompetitive manner. Furthermore, GABA receptors of horizontal cells were modulated by extracellular application of diazepam, zolpidem, methyl 6,7-dimethoxy-4-ethyl-β-carboxylate, pentobarbital, and alphaxalone, thus showing typical pharmacological properties of CNS GABAAreceptors. GABA-evoked single-channel currents were characterized by a main conductance state of 29.8 pS and two subconductance states (20.2 and 10.8 pS, respectively). Kinetic analysis of single-channel events within bursts revealed similar mean open and closed times for the main conductance and the 20.2-pS subconductance state, resulting in open probabilities of 44.6 and 42.7%, respectively. The ratio of open to closed times, however, was significantly different for the 10.8-pS subconductance state with an open probability of 57.2%.
Comparative Morphology of Rodent Vestibular Periphery. I. Saccular and Utricular Maculae
Authors: Desai Sapan S. , Zeh Catherine , Lysakowski Anna
Published: July 2004

Calyx afferents, a group of morphologically and physiologically distinct afferent fibers innervating the striolar region of vestibular sensory epithelia, are selectively labeled by antibodies to the calcium-binding protein calretinin. In this study, the population of calretinin-stained calyx afferents was used to delineate and quantify the striolar region in six rodent species: mouse, rat, gerbil, guinea pig, chinchilla, and tree squirrel. Morphometric studies and hair cell and calyx afferent counts were done. Numbers of hair cells, area, length, and width of the sensory epithelium increase from mouse to tree squirrel. In the mouse and rat, calretinin is found in 5–9% of all type I hair cells, 20–40% of striolar type II hair cells, and 70–80% of extrastriolar type II hair cells. Numbers of calyx afferents increase from mouse to squirrel, with more complex calyx afferents in larger species. About 10% of calyx afferents are branched. Based on our counts of total numbers of calyx afferents in chinchilla maculae and in comparison to fiber counts in the literature, the proportion of calyx afferents is greater than previously described, constituting nearly 20% of the total. Because morphometric measures increase with body weight, we obtained additional data on vestibular end organ surface areas from the literature and used this to construct a power law function describing this relationship. The function holds for species with body weights less than ∼4 kg. Greater than 4 kg, the surface area of the sensory epithelia remains constant even with increasing body weight.
Compressive Behaviour of Corrugated Board Panels
Authors: Lu T. J. , Chen C. , Zhu G.
Published: July 2004

The compressive responses and failure mechanisms of corrugated sandwich panels subjected to uniform lateral compression are examined by a combined theoretical and experimental study. Particular focus is placed on illuminating the role of the initially sinusoidal fluting in dominating the overall deformation and local collapse of the board panel. Two types of specimen are considered, FCT (Flat Crush Test) specimen and CMT (Concorra Medium Test) specimen; the former is cut directly from the panel whilst the latter consists of a fluting, a thin glued tape but no outliners (face sheets). Both specimens are modelled by curved beam elements and surface contact elements (including sticky contact elements for the CMT specimen), and the elastoplastic material is idealised by a bi-linear constitutive model satisfying the J2-flow theory. Finite element calculations are first made to study the effect of replacing the periodic boundary conditions with free-edge boundary conditions on the deformation of a unit cell. Extensive calculations are then performed to obtain the compressive strength of each specimen as a function of geometrical and material parameters, and to study the global and local plastic collapse mechanism during the deformation process. The effect of manufacturing-induced geometrical imperfections on the mechanical properties of the board panel is also quantified. Experimental measurements are conducted on two types of commercially available corrugated board panel to check the validity of analytical predictions.
Effective Moduli of Woven Composites
Authors: Whitcomb John , Tang Xiaodong
Published: July 2004

The objectives of this paper are: (1) to identify the dominant characteristics of a weave that govern the engineering properties; (2) to explain why certain behaviors of weave are observed; and (3) to evaluate a very simple building block strategy for estimating the effects of waviness on engineering properties. Based on the hypothesis that complexities in the mechanical response are encapsulated in the wavy regions, factors such as undulated tow length and material rotation angles are investigated to see how they affect the effective properties as a function of waviness. Simple formulas that ignore the “bridging effects” are proposed for Exx, Ezz,. xz and Gxz. Results from the simple formulas are compared with three-dimensional finite element results for three satin weaves and a twill weave and for two material systems.
Delamination Analysis of Layered Shells
Authors: Babaei R. , Epstein M. , Lukasiewicz S. A.
Published: July 2004

This article provides a theoretical and numerical treatment of delaminations in composite shells. A large deformation theory for layered shells of arbitrarily varying thickness, including interface delamination and transverse shear effects, is developed. Asystem of layer coordinates and conjugate coordinates is introduced which allows the results to be presented in a simple compact form analogous to the theory of monocoque shells. To validate the feasibility and the accuracy of the developed theory, a numerical example is provided. The results of the present theory are compared for a one dimensional beam with results obtained from two dimensional finite element analysis and excellent agreement is observed.
Damage Tolerance Analysis of Cracked Stiffened Composite Panels
Authors: Chen Puhui , Shen Zhen , Wang Junyang
Published: July 2004

An approach based on a displacement compatibility model is developed for stiffened composite panels with a crack. Some important improvements on the damage tolerance analysis of the stiffened composite panels have been made in comparison with previous work. Some new results are obtained regarding the effects of adhesive nonlinearity, stringer stiffness and bending, and stringer spacing on strengths and crack growth behaviours of bonded skin/stringer panels. The study indicates that the adhesive nonlinearity benefits the load bearing capacity of the panels. When the stringer is quite thick in comparison to the skin thickness, its out-of-plane bending will lower panel failure strains. Increasing stringer stiffness can not often guarantee the high failure strains of bonded skin/stringer composite panels. As the stringer stiffness exceeds some value, its increase has a negative effect on the load bearing capacity of the panels. For a given ratio of stringer stiffness to panel stiffness, the failure strains of the panels increase as stringer spacing, Wa, decreases. Predictions for failure strains and crack arrest capability agree well with experimental results for several composite panel configurations.
Predicting the In-plane Elastic Constants of Diamond Braided Composites
Authors: Aggarwal A. , Ramakrishna S. , Ganesh V. K.
Published: July 2004

An analytical model based upon repeat unit cell approach is proposed to predict the in-plane elastic constants of two dimensional diamond braided composites. A new geometrical model is developed which considers the yarn undulation and inter-yarn gap in a diamond braided fabric reinforced composite. The actual state of yarns in composites is modeled by the use of sinusoidal shape functions, which employ parameters such as braid construction, yarn geometry, inter-yarn gap and overall volume fraction to quantify the geometry of braided fabric. Stiffness is predicted by calculating the engineering constants for each subcell followed by averaging it over the repeat unit cell’s volume using a combination of iso-stress and iso-strain conditions. Composites using four different fabric architectures are fabricated and tested in tensile mode to verify the model. The experimental results indicate reasonable correlation with predicted results. Parametric study is conducted over a range of structurally possible geometrical parameters to study the effects of braiding angle, yarn aspect ratio and gap on the in-plane elastic properties of the textile composite.
Effect of Various Parameters on the Effective Properties of a Cracked Ply
Authors: Noh Jae , Whitcomb John
Published: July 2004

Damage in composite materials accumulates in a diffuse manner. Accounting for this damage in a progressive failure analysis requires an accurate measure of the degraded stiffness coefficients. This paper describes micromechanics models for predicting the effect of distributed cracks on the engineering properties (extensional moduli, shear moduli, and Poisson’s ratios). Quasi-3D and 3D finite element methods were employed to determine the effective material properties of the cracked ply. Analyses were performed for various material systems, damage states, and adjacent (to the cracked ply) ply properties. The results show that the effective properties of cracked ply are very sensitive to the initial properties of a cracked ply. These properties are also found to be sensitive to the adjacent ply properties and orientation. However, they are not much affected by cracks in the adjacent plies. Relationships describing the sensitivity of the effective properties to the adjacent ply properties and the initial properties of a cracked ply were obtained. These relationships are useful for explaining the degradation behavior of laminates. Quantitative measures are presented for the errors introduced when shear-extension-coupling terms are ignored when calculating effective properties. Also, it was proven that transverse matrix cracks only affect the diagonal terms in the effective compliance matrix for certain configurations.
Material Behavior of Structural Reaction Injection Molded Composites under Thermomechanical Loading
Authors: Eason T. G. , Ochoa O. O.
Published: July 2004

The damage initiation and growth in discontinuous random fiber composites is explored with a representative volume element (RVE). Atensile loading condition is used to illustrate the effect of thermal processing on damage initiation and progression. The RVE utilizes a moderate strain elasto-plastic-fracture constitutive formulation for the resin as a function of temperature. The constitutive response of the fiber is modeled as linear elastic with fracture. The constitutive formulation is implemented into a commercial finite element program, ABAQUS®, as a user material subroutine to track damage initiation and growth within the RVE. This allows the designer to develop an understanding between the resin and fiber properties (coefficient of linear thermal expansion, yield stress, fracture strain, modulus) on the mechanical performance of random fiber composites.
Impregnation of Compressible Fiber Mats with a Thermoplastic Resin. Part I: Theory
Authors: Michaud V. , Månson J. -A. E.
Published: July 2004

In many cases of composite processing by liquid matrix impregnation, the fiber reinforcement is compressed when it comes in contact with the liquid and then relaxes as the matrix flows within its pores. This phenomenon can be analyzed in terms of local fluid flow, mass conservation and mechanical equilibrium. A model is proposed to simulate the kinetics of impregnation, and the evolution of the fiber volume fraction profile as the resin front progresses, as well as after the front has reached the end of the mold. The analysis is then applied to the case of infiltration of needled glass fiber preforms by a polypropylene matrix, used in the production of Glass Mat Thermoplastic blanks. Aquantification of the effects of applied pressure and fluid viscosity on total process time is provided. It is shown that the time for preform relaxation after the fluid has filled the preform may be much larger than that for impregnation. As a result, an apparently well impregnated part may exhibit an inhomogeneous distribution of the reinforcement, in turn inducing a modification of the mechanical behavior and residual stress distribution.
Analysis of Composite Bonded/Bolted Joints Used in Repairing
Authors: Chan Wen S. , Vedhagiri S.
Published: July 2004

The performance of composite repairing using single lapped joints is sensitive to factors such as ply stacking sequence of laminate, bonding surface preparation, anisotropic nature of adherend, as well as bearing and load transfer from one adherend to the other.

This research is focused to investigate the stress distributions in laminated composite joints with multiple pin loads using finite element analysis. The structural response of various configurations of single lap joints, namely bonded, bolted and bonded-bolted joints, are analyzed by three-dimensional finite element method.

A comparison of the results obtained using finite element analysis is conducted with experimental results and the results are validated. Parametric study is conducted to investigate the effect of stress distribution and load transfer due to ply stacking sequence of laminate.
A Model for the Recovery of Thermomechanical Properties in Strongly Anisotropic Damaged Materials
Authors: Thionnet A.
Published: July 2004

Damage decreases the mechanical characteristics of materials and also modifies their thermal properties. However these modifications can disappear when the microcracks are closed. Wepropose amodel of this phenomenon for the thermomechanical behavior of strongly anisotropic materials. The aim of this work is to adapt the concept of loading mode in Fracture Mechanics to Damage Mechanics and to include it explicitly in the equations. This allows to obtain a thermomechanical behavior respecting rigorously all the criterions, notably the continuity and the deactivation of each modulus that are necessary for the consistency of the modeling of the damage phenomenon. In particular, contrary to the other ways of modeling, it simulates the Poisson effect restoration and according to case studies does restore or does not restore the shear modulus without adding a friction law on the microcracks.
Refining Estimates of Major Depression Incidence and Episode Duration in Canada Using a Monte Carlo Markov Model
Authors: Patten Scott B. , Lee Robert C.
Published: July 2004

Background. Serial period prevalence estimates for recurrent diseases such as major depression are available more frequently than fully detailed longitudinal data, but it is difficult to estimate incidence and episode duration from such data. Incidence and episode duration are critical decision modeling parameters for recurrent diseases. Objectives. To reduce bias that would otherwise occur in national incidence and duration-of-episode estimates for major depressive episodes deriving from studies using serial period prevalence data and to illustrate amethodological approach for the estimation of incidence from such studies. Methods. Monte Carlo simulation was applied to a Markov process describing incidence and recovery from major depressive episodes. Results. The annual incidence and episode duration were found to be 3.1% and 17.1 weeks, respectively. These estimates are expected to be less subject to bias than those generated without modeling. Conclusions. These results highlight the usefulness of Markov models for analysis of longitudinal data. The methods described here may be useful for decision modeling andmay be generalizable to other chronic diseases.
Innovative Fracture Tests of Single-Lapped Bolted and Bonded Composite Joints
Authors: Jen Ming-Hwa R. , Lin Wei-Hwang
Published: July 2004

The fracture tests of single-lapped and bolted and bonded mixed composite joints subjected to tension by using U.S. patented new model clip are systematically investigated. The failure load of those joints tested by conventionally clip of universal material testing machine are over-estimated by comparison, mainly attributed to the joint adherends are parallel but not in a line. Herein, the innovative clip of U.S. patent is introduced and manufactured in parametric study to generate the true value of strength of single-lapped mixed composite joint.

Two types of lay-ups, such as cross-ply and quasi-isotropy, are used as adherends in composite joint. Single-lapped joint, riveted and bonded joint, and bolted and bonded joint with the varieties of clamping force, overlap length, gage length and fastener's properties are tested to yield the joint failure load, failure mechanism and feature behavior. A system of devices is disclosed to measure the clamping force that promotes the capability to analyze the complicated joint problem. Through a series of tests our achievements are highlighted. The joint failure load measured by new model clip (N-clip) is lower than that by conventional MTS clip (M-clip), i.e., previously used failure load is overestimated and the realistic failure load is lower. The joint of cross-ply adherend is always stronger than that of quasi-isotropic adherend. The overlap length in the single-lapped and mixed joints is a dominant factor. The failure load increases with increasing of overlap length until it reaches an asymptotical value when over three widths. Finally, the more clamping force is applied, the stronger the mixed joint is. Nevertheless, the bolted and bonded joint is always stronger than the riveted and bonded joint in the same testing conditions.
Effect of Pulling Speed on the Sizes of the Liquid, Gel and Solid Zone During Thermoset Pultrusion
Authors: Atarsia Abdelatif , Boukhili Rachid
Published: July 2004

The temperature and the degree of cure distributions inside a thermoset composite profile during the pultrusion process are calculated numerically using the finite difference method. The degrees of cure at the beginning of the gel and the solid zones i.e., OCGL and CLGs are determined using appropriate experimental techniques. These results enabled us to predict the location and the size of the liquid, gel and solid zones inside a pultrusion die. It is found that the pulling speed affects the size and the position of each zone considerably. The relationships between the sizes of these zones and the pull-force is discussed.
ESCR Behavior of Plastic Materials in Medical Environments
Authors: Qin Chuan , Ding Y. S. , Dhyani H. , Kivlehan T. , Hong K. Z. , Monaghan M. , Penn J. , Woo L.
Published: July 2004

Besides other facets of product development, it is imperative for medical device manufacturers to take great efforts through proper evaluation and consideration of material properties under practical conditions to prevent product failure at the end-uses. The environmental stress crack (ESCR) induced by chemical agents plays a significant role on material performances. In this contribution, in-depth studies have been carried out on different medical plastic materials, such as polycarbonate, copolyesters, ABS, acrylics, rigid thermoplastic polyurethane and their blends. More attention will be focused on a copolyester material for its unique ESCR behavior. Variation of chemical agents (such as different types of hospital disinfection solutions) have great impacts on physical and functional properties. Various plastics shows distinct environmental stress cracking phenomena under different conditions. Mechanisms of ESCR phenomenon under different environments have been explored. Fibril reinforcement by cold crystallization and chain session by hydrolysis of the copolyester may have contributed to its excellent chemical resistance against a wide range of chemicals and its catastrophic failure in acidic or basic environment. In addition, appropriate definition of product failures is also critical in making materials decisions.
Experimental Validation of Morphology Simulation in Glass Fibre Reinforced Polycarbonate Discs
Authors: Neves N. M. , Pontes A. J. , Pouzada A. S.
Published: July 2004

As assessment is made between Moldflow simulations and experimentally determined fibre orientation distributions at three points along the flow path and 12 layers across the thickness. The material used is a 10% weight by weight short glass fibre reinforced polycarbonate. With this material the physical interaction between fibres during flow is minimised. Centre gated circular discs, where both the shear and the extensional flows are present, were produced over a range of moulding conditions to analyse the effect of flow rate and melt temperature upon the fibre orientation.

The fibre orientation was measured using image analysis tools in images obtained by reflection microscopy of polished sections, using the method proposed by Bay. The measurements were made in 12 layers across the thickness.
Low-Velocity Impact Response and Dynamic Characteristics of Glass-Resin Composites
Authors: Mantena P. Raju , Mann Richa , Nori Chandrasekhar
Published: July 2004

This paper describes a test methodology used for characterizing different glass-resin composite systems with respect to their low-velocity impact response, dynamic modulus and inherent damping properties. Impact tests were conducted on SMC plaque samples in an instrumented impact test machine. A Dynamic Mechanical Analyzer was used for testing small rectangular samples in the fixed frequency mode of operation. An impulse-frequency response vibration technique was used for obtaining the dynamic modulus and loss factor of cantilever beam specimens at ambient conditions. The dynamic modulus, glass transition and damping peak intensities obtained from the DMA and the vibration techniques are correlated with the impact test data. The potential application for screening glass-resin formulations with respect to their impact performance is discussed.
Fatigue Life Predictions in Woven Carbon Fabric/Polyester Composites Based on Modulus Degradation
Authors: Khan Z. , Al-Sulaiman F. A. , Farooqi J. K. , Younas M.
Published: July 2004

An analytical model, based on stiffness degradation during fatigue loading, which has been used for fatigue life predictions in the Fiber Reinforced Plastics (FRP), is employed to examine its validity to the fatigue life predictions in the Woven Fabric Reinforced Plastics. The rate of stiffness degradation ( dE/dN) has been obtained from the constant amplitude fatigue testing of 8-ply coupons made from prepreg plainweave woven carbon fabric having a polyester resin as the matrix material. The test coupons had three different ply stacking sequences, namely, the unidirectional (0)8, and two off axis plied (0,0,+45,-45) s, and (+45,-45,0,0) s orientations. The estimated fatigue lives obtained from the damage rate function dD/dN, which in turn was a function of the stiffness degradation rate dE/dN, were compared with the experimentally observed fatigue life data. It is shown that the stiffness degradation model provides reasonably good correlation between the analytically determined fatigue lives and the experimentally observed fatigue lives for the plain-weave woven Carbon Fabric Reinforced Plastic Composites.
Potentiality of Pineapple Leaf Fibre as Reinforcement in PALF-Polyester Composite: Surface Modification and Mechanical Performance
Authors: Mishra S. , Misra M. , Tripathy S. S. , Nayak S. K. , Mohanty A. K.
Published: July 2004

This paper is an attempt to examine the commercial signficance of an agro-waste “Pineapple Leaf Fibre” (PALF) which is rich in cellulose, relatively inexpensive and has the potential for polymer reinforcement. The quality enhancement of PALF has been tried through different surface modifications like dewaxing, alkali treatment, cyanoethylation and grafting of AN onto dewaxed PALF. The present study investigated the mechanical propeties like tensile, flexural and impact behavior of PALF-reinforced polyester composites as a function of fibre loading and fibre surface modification. The mechanical properties are optimum at a fibre loading of 30 wt%. Among all modifications, 10% AN grafted PALF composite exhibited maximum tensile strength (48.36 MPa) whereas cyanoethylated PALF composite exhibited better flexural and impact strength, i.e., 41% and 27% more than the control (detergent washed composite) respectively. Scanning electron microscopic studies were carried out to understand the fibre-matrix adhesion.
Chemical Resistance and Tensile Properties of Epoxy/Polycarbonate Blend Coated Bamboo Fibres
Authors: Rajulu A. Varada , Rao G. Babu , Reddy R. Lakshminarayana , Sanjeevi R.
Published: July 2004

The bamboo fibres belonging to the family of Dendrocalamus strictus were coated with a blend of epoxy/polycarbonate with varying polycarbonate content. The chemical resistance of these fibres to some acids, alkalis and solvents was studied. The tensile load at break for these fibres was determined. The coated fibres showed higher tensile load at break, and were resistant to acids and alkalis. However, the solvent resistance of the coated fibres was found to be minimal.
Study on the Post-Buckling Behavior of Laminates Connected by Rivets
Authors: Lee Ya-Jung , Lin Huei-Jeng , Lin Ching-Chieh
Published: July 2004

The present study employs a numerical approach to investigate the post-buckling behavior of laminates connected by rivets. In order to reduce the calculation time, the rivets are replaced with springs, while the stiffness of the springs is induced from the study that analyzes the bending behavior and the interaction between the rivet and the laminate. The finite element software ABAQUS is used to inspect the post-buckling behavior of composite laminates connected by rivets. Several parameters are considered like the stacking sequence, the arrangement of the rivets, and the span between the stiffener. In all these cases, springs can fully present the behavior around the rivets. Finally, the validity of this method is verified by experiment.
Compressive Strength of Composite/Concrete Cylinders after Low Energy Impact
Authors: Liu Hsien-Kuang , Tai Nyan-Hwa , Chen Zhi-Cheng
Published: July 2004

This paper deals with the repair of the concrete cylinder by fiber reinforced composites fabricated through the filament winding method. Composites fabricated by the method can reinforce concrete cylinders efficiently because they provide comprehensive and multi-axial reinforcing effects. In this work, three winding angles were adopted to wind six layers of glass/epoxy composite jacket onto the concrete cylinder. These three winding angles combined with different lay-up sequence form seven types of composite/concrete cylinders. The compression after impact (CAI) test was conducted on the seven composite/concrete cylinders. These experiments were designed to investigate the influence of winding angles and lay-up sequence of the composite on the CAI strength. It is found that the highest CAI strength among the composite wound concrete cylinder is 4.81 times higher than that of the concrete cylinder without the reinforced composite. In addition, the former has higher failure strain than the latter. The impact resistance can be evaluated by a compression after impact/compression before impact (CAI/CBI) strength ratio. It is also detected that although impact damage has been introduced, the fracture of composite/concrete cylinder under compression may not be initiated from the impact site. Moreover, the failure strengths are influenced by damage mechanisms of the cylinders, and the damage modes for the concrete cylinder and wound composites are related. In this paper, the damage mechanisms of different wound concrete cylinders under CAI test were discussed.
Measurement of Dispersion of Glass Beads in PP Matrix
Authors: Liang J. Z. , Li R. K. Y.
Published: July 2004

The dispersion of rigid inorganic particles (RIP) in polymer matrix is discussed and an equation for estimation of the dispersion is proposed. The dispersion of glass beads (GB) in polypropylene (PP) matrix and PP/ethylene-propylene-diene monomer co-polymer (EPDM) blend was measured by means of thermogravimetric analysis (TGA). It was found that the effects of the filler surface treatment and modification on the uniformity of the glass beads in the PP matrix was insignificant at low filler concentration. But the dispersion for the PP filled with the small glass beads was better than that of the big GB-filled system. Moreover, the values of the measured weight fraction of the glass beads were somewhat lower than those of the calculations for PP/EPDM/GB hybrid composites. In other words, no obvious cluster or aggregation phenomenon of the glass beads in the matrix occurs for these systems. It suggests that the uniformity of the glass bead dispersion for PP/EPDM/GB systems is relatively better than that of PP/GB systems.
Strength of Concrete Cylinder Confined by Composite Materials
Authors: Lin Huei-Jeng , Chen Chin-Ting
Published: July 2004

This paper investigates the strength of concrete cylinders confined by composites in three different ways. First, the relationship between number of composite layers and strength of confined concrete cylinder is studied. Carbon and glass fiber composites are used for confinement. Experimental results indicate that strength of the confined concrete cylinder increases in direct proportion to the number of layers of composites. Second, the stacking sequence effect from wrapping the concrete column with carbon and glass fiber together is studied. According to those results, the closer the glass composite is to the concrete cylinder implies a higher strength of the confined concrete cylinder. Third, this investigation attempts to partially wrap the concrete cylinder with carbon and glass fiber to investigate how the various wrapping methods differ. In addition, the strength of the reinforced concrete cylinder is also predicted. A simple failure model is derived from observing the experimental phenomena. Results by the simple model and the models developed to date are analyzed and compared with experimental data. The proposed simple model has more closely corresponded to the experiments.
Effects of Inertia Forces on Elastothermodynamic Damping of Fibre-Reinforced Metal-Matrix Composites
Authors: Srivastava S. K. , Mishra B. K. , Jain S. C.
Published: July 2004

When a thermoelastic material is subjected to a time varying stress field, the mechanical energy is dissipated in the form of heat due to the well-known thermoelastic effect. This process is known as elastothermodynamic damping. Evaluation of elastothermodynamic damping in fibre-reinforced MMCs has been reported in literature. These works follow a quasi-static approach. In the present work, a full dynamic solution incorporating the inertia forces has been presented. The effect of inertia forces on elastothermodynamic damping of fibre-reinforced MMCs is found to be more significant at high excitation frequencies, for large fibre radius and low fibre volume fraction.
Stress and Failure Analysis of 3D Orthogonal Interlock Woven Composites
Authors: Naik N. K. , Azad Sk. N. M. , Prasad P. Durga , Thuruthimattam B. J.
Published: July 2004

A three-dimensional woven composite strength model is presented for predicting the failure behavior of three-dimensional orthogonal interlock woven composites under on-axis uniaxial static tensile loading and shear loading. The model is based on two-level discretization of the repeating unit cell. The repeating unit cell is discretized into sections, elements, subsections and subelements. The model predicts the stress levels at which the secondary failures take place at subelement level. The effect of secondary failure is considered for further analysis and the ultimate tensile strength and shear strength and the corresponding strains are predicted. A parametric study has been carried out for different 3D orthogonal interlock woven composite configurations. In general, it is seen that there is no significant reduction in the inplane elastic and strength properties for 3D orthogonal woven composites, compared to the corresponding cross-ply laminates made of unidirectional layers, but there is a significant increase in the through-the-thickness properties.
Progressive Failure Analysis of Laminated Plates with Delamination
Authors: Sun Xiannian , Tong Liyong , Chen Haoran
Published: July 2004

A numerical methodology on simulating progressive compressive failure of delaminated plates is presented. A finite element code based on the Reissner-Mindlin plate theory and the Von Karman’s nonlinear plate theory is developed to simulate initial buckling, postbuckling, contact effect of delamination front, delamination growth, fiber-breakage and matrix cracking. Delamination growth is taken into account by applying a fracture mechanics criterion which checks the strain energy release rate (SERR) along the delamination front. Meanwhile, fiber-breakage and matrix cracking are analyzed by a stiffness degradation scheme. Some numerical examples are presented to illustrate different failure mode of delaminated plates. It is found that the delamination growth is significantly affected by the boundary condition, and the stiffness degradation plays an important role in the strength analysis of delaminated plate.
Calcium Dynamics and Circadian Rhythms in Suprachiasmatic Nucleus Neurons
Authors: Ikeda Masayuki
Published: July 2004

The hypothalamic suprachiasmatic nucleus (SCN) has a pivotal role in the mammalian circadian clock. SCN neurons generate circadian rhythms in action potential firing frequencies and neurotransmitter release, and the core oscillation is thought to be driven by “clock gene” transcription-translation feedback loops. Cytosolic Ca2+ mobilization followed by stimulation of various receptors has been shown to reset the gene transcription cycles in SCN neurons, whereas contribution of steady-state cytosolic Ca2+ levels to the rhythm generation is unclear. Recently, circadian rhythms in cytosolic Ca2+ levels have been demonstrated in cultured SCN neurons. The circadian Ca2+ rhythms are driven by the release of Ca2+ from ryanodine-sensitive internal stores and resistant to the blockade of action potentials. These results raise the possibility that gene translation/transcription loops may interact with autonomous Ca2+ oscillations in the production of circadian rhythms in SCN neurons.
Electrical Signaling in Central Orexin/Hypocretin Circuits: Tuning Arousal and Appetite to Fit the Environment
Authors: Burdakov Denis
Published: July 2004

In mammals, alertness and foraging are linked to the light-dark cycle and body energy levels. This link is crucially dependent on the novel peptide transmitters orexins/hypocretins. The firing of orexin neurons encodes the overall internal (body energy levels) and external (time of day) environment. In turn, orexins modulate arousal and appetite by innervating and electrically exciting wakeand appetitepromoting neurons. Electrical signaling in orexin circuits thereby couples arousal to the environment and synchronizes foraging with states of high alertness.
Spina Bifida
Authors: Wingate Elke E. , Hancock Jody Arnold , Churchwell Kelley E. , Pipkins Monica J.
Published: July 2004

Spina bifida is a serious birth defect that involves an incomplete closure of the spine, spinal cord, brain, and/or protective covering of the fetal spine. Even though the causes of spina bifida are still uncertain, diabetes, obesity, severe hyperthermia in early pregnancies, and poor nutrition are believed to be causes of neural tube defects (NTDs). Because spina bifida may go undetected by •-fetoprotein screening and amniocentesis, sonography becomes a valuable tool in its identification. Spina bifida can also affect the fetal brain, so sonography is important in detecting any abnormal fetal head signs associated with Arnold-Chiari (type II) malformation. Surgical planning is another important part of sonography’s role when detecting NTDs. Although still in experimental stages, in utero repair has proven beneficial in some cases of spina bifida after careful sonographic assessment as part of the treatment considerations.
The Historical Foundation of the SDMS Code of Ethics
Authors: Boodt Cheryl L.
Published: July 2004

Sonographers are a part of a complex health care system in the United States. Since health care’s earliest days millennia ago, those outside and inside health care have seen the need to have a code of ethics to protect the public and enhance the efficacy of health care. This article gives a brief history of medical ethics and its four pillar principles: beneficence, nonmaleficence, autonomy, and justice. The American Registry of Diagnostic Medical Sonographers provided the impetus for a sonography coalition, composed of several related organizations, to develop a code of ethics for the new profession. The board of directors of the Society of Diagnostic Medical Sonography (SDMS) adopted it without modifications in 1995. Currently, the SDMS board is reevaluating and considering modifications to the current document. The SDMS Code of Ethics is a statement of the moral and ethical principles on which sonography practice is based.