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At least 307 records · Page 17Linked to original sources

PubMed2005

Structural characterization of the chordae tendineae in native porcine mitral valves.

BACKGROUND: This study was aimed to characterize the different mitral valve chordae tendineae to provide additional understanding of their function. METHODS: Mitral valve chordae tendineae from fresh porcine hearts were stained for collagen and elastin using either a Verhoeff and van Gieson stain or Verhoeff light green stain. Cellular distribution was determined using a hematoxylin and eosin stain. Immunohistochemistry was used to verify the findings of vasculature. Biochemical assays were performed to quantify DNA, collagen, and elastin content of each of the six different types of chordae tendineae. RESULTS: Blood vessels were observed in the longitudinal and circumferential directions of the chordae. The strut chordae on the anterior leaflet of the mitral valve showed an increased degree of vascularization compared with the other chordae. All chordae had an inner layer characterized by a high concentration of collagen and an outer layer that was mostly elastin with interwoven collagen fibers. The collagen microstructure was characterized by directional crimping. Hematoxylin and eosin staining showed fibroblasts evenly distributed throughout the inner and outer layer of the chordae tendineae. Quantitative analysis showed significantly higher levels of DNA and collagen content in the anterior and posterior marginal chordae compared with the other chordae. CONCLUSIONS: The chordae tendineae were seen to have different microstructures according to chordal type. The presence of vessels characterized the chordae tendineae as complex living components that work in coordination with the papillary muscles and mitral valve leaflets to prevent mitral valve prolapse and regurgitation. They may also function to supply nutrients to the valve leaflets.

Animals↗

PubMed2004

Determining the effectiveness of conventional and alternative coagulants through effective characterization schemes.

Polymeric forms of metal coagulants in water treatment have become increasingly used due to their wider availability and reduction in cost. These specialized coagulant forms and products are claimed by manufacturers to be superior to conventional coagulants in particulate and/or organic removal with inherent advantages of lower alkalinity consumption and lesser sludge production. However, due to their proprietary nature, little is known about their chemical composition. To determine and understand the effectiveness of these alternative coagulants, a comprehensive study was undertaken to characterize metal coagulants, and to comparatively evaluate them on a well-characterized source water. The objective of this study was to provide a scheme for utilities that could be employed as a screening process and a method of selecting an appropriate coagulant based on raw water characteristics and insight into the coagulatability of the source water. Characterizations of coagulants included: (i) active metal content, (ii) anion content, (iii) acidity, (iv) alkalinity consumption, (v) charge reversal by colloidal titration, and (vi) molecular weight determination. A total of five poly-aluminum chlorides (PACl), along with a conventional coagulant (aluminum sulfate or alum) were evaluated. Results show that through the characterization scheme, an effective coagulant (conventional versus alternative) and coagulant type (among various PACl) can be chosen before undertaking time-consuming bench or pilot-scale evaluation.

Aluminum Compounds↗

PubMed2005

Characterization of Fusarium spp. isolates by PCR-RFLP analysis of the intergenic spacer region of the rRNA gene (rDNA).

In the present study, 44 Fusarium spp. isolates (5 Fusarium culmorum, 7 Fusarium graminearum, 1 Fusarium cerealis, 1 Fusarium poae, 26 Fusarium oxysporum, and 4 Gibberella fujikuroi species complex) were characterized morphologically, physiologically and genetically. All except one (Dutch Collection: CBS 620.72) were isolated from different hosts grown in various Spanish localizations. Morphological characterization was made according to macroscopic and microscopic aspects. Physiological characterization was based on their ability to produce zearalenone (ZEA) and type B trichothecenes (deoxynivalenol, nivalenol and 3-acetyldeoxynivalenol). ZEA was determined by liquid chromatography and trichothecenes by gas chromatography. Confirmation was carried out by liquid chromatography-ion trap-mass spectrometry (ZEA) or gas chromatography-mass spectrometry (trichothecenes). Molecular characterization of isolates was performed using an optimized, simple and low-cost method for isolation of DNA from filamentous fungi and polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) of the intergenic spacer region (IGS) of the rRNA gene (rDNA). The results indicate that F. graminearum, F. culmorum and F. cerealis isolates were high ZEA and type B trichothecene producers, the F. poae isolate produced very low level of nivalenol while F. oxysporum and the G. fujikuroi complex isolates did not show this ability. Restriction patterns of the IGS region did not show any relationship with the host, geographic origin of the isolate and mycotoxin-producing capacity. However, the haplotypes obtained with six restriction enzymes (CfoI, AluI, HapII, XhoI, EcoRI and PstI) permitted to discern the six assayed Fusarium species. Therefore, this is a rapid and suitable methodology that allows closely related strains to group and to estimate the genetic relationships between the groups.

Cluster Analysis↗

PubMed2005

Application of TZERO calibrated modulated temperature differential scanning calorimetry to characterize model protein formulations.

The objective of this study was to evaluate the feasibility of using T(ZERO) modulated temperature differential scanning calorimetry (MDSC) as a novel technique to characterize protein solutions using lysozyme as a model protein and IgG as a model monoclonal antibody. MDSC involves the application of modulated heating program, along with the standard heating program that enables the separation of overlapping thermal transitions. Although characterization of unfolding transitions for protein solutions requires the application of high sensitive DSC, separation of overlapping transitions like aggregation and other exothermic events may be possible only by use of MDSC. A newer T(ZERO) calibrated MDSC model from TA instruments that has improved sensitivity than previous models was used. MDSC analysis showed total, reversing and non-reversing heat flow signals. Total heat flow signals showed a combination of melting endotherms and overlapping exothermic events. Under the operating conditions used, the melting endotherms were seen in reversing heat flow signal while the exothermic events were seen in non-reversing heat flow signal. This enabled the separation of overlapping thermal transitions, improved data analysis and decreased baseline noise. MDSC was used here for characterization of lysozyme solutions, but its feasibility for characterizing therapeutic protein solutions needs further assessment.

Buffers↗

PubMed2005

Molecular cloning and characterization of Ras- and Raf-homologues from the fox-tapeworm Echinococcus multilocularis.

To better understand growth regulation in the human parasitic cestode Echinococcus multilocularis, we have cloned and characterized the parasite's orthologues of the key regulatory factors Ras and Raf. Using a degenerative PCR approach a gene, emras, was identified whose gene product, EmRas, showed high homology (79% identical residues) to human Ras and contained all amino acid residues which are characteristic for this subfamily of small GTPases at the corresponding positions. Recombinantly expressed EmRas bound GTP and was farnesylated, but not geranyl-geranylated, by Echinococcus lysate in an in vitro prenylation assay. Furthermore, upon expression in yeast, emras was able to functionally complement the Saccharomyces orthologue RAS2 in an invasive growth assay. In Western blot analyses using an anti-EmRas antibody, the Echinococcus factor could be detected in lysates of the larval stages metacestode and protoscolex. By immune-histochemistry, EmRas was shown to localize to the germinal layer of the metacestode and to tegumental structures of the protoscolex, particularly around the rostellum and the sucker regions. In addition, we fully characterized the gene emraf whose product, EmRaf, displayed considerable homology to mammalian Raf-kinases and orthologous factors from Drosophila and Caenorhabditis elegans. emraf was co-expressed with emras in the larval stages metacestode and protoscolex during in vitro cultivation and during an infection of the intermediate host as assessed by RT-PCR experiments. The emraf gene was composed of nine exons and eight introns and shared four highly conserved exon-intron boundaries with the human gene encoding Raf-1, suggesting that both genes derived from a common evolutionary ancestor. Southern blot hybridizations demonstrated that emraf is a single copy gene. Using the yeast two-hybrid system, EmRaf was shown to interact with EmRas, but not with EmRal, a previously characterized orthologue of mammalian Ral GTPases. This is the first characterization of a Ras orthologue from a cestode and the first report on a Raf-like kinase from a platyhelminth. The data presented herein will form a solid basis for further investigations on Echinococcus signaling systems that are involved in growth control and development of the parasite.

Amino Acid Sequence↗

PubMed2006

Characterization of green fluorescent protein-expressing retinal cells in CD 44-transgenic mice.

Sensory information in the retina is transferred from rod and cone photoreceptors to higher visual centers via numerous parallel circuits that sample the photoreceptor mosaic independently. Each circuit consists of a unique combination of ganglion cell, bipolar and amacrine cell types. The morphology and physiological responses of many amacrine cells have been characterized. However, the synaptic connections and retinal circuits in which they participate are only rarely understood. A major problem that has prevented fuller characterization of retinal circuitry is the need for specific cellular markers for the more than 50 inner retinal cell types. One potential strategy for labeling cells is to use transgenic expression of a reporter gene in a specific cell type. In a recent study of cluster of differentiation 44 (CD44)-enhanced green fluorescent protein (EGFP) transgenic mice, we observed that the green fluorescent protein (GFP) was expressed in a population of amacrine and ganglion cells in the inner nuclear layer (INL) and the GCL. To characterize the morphology of the GFP-labeled cells, whole mount preparations of the retina were used for targeted iontophoretic injections of Lucifer Yellow and Neurobiotin. Furthermore, immunocytochemistry was used to characterize the antigenic properties of the cells. We found that many GFP-expressing cells were GABAergic and also expressed calretinin. In addition to the somatic staining, there was a strong GFP(+)-band located about 50-60% depth in the inner plexiform layer (IPL). Double labeling with an antibody to choline acetyltransferase (ChAT) revealed that the GFP-band was located at strata 3 inner retina. The best-labeled GFP-expressing cell type in the INL was a wide-field amacrine cell that ramified in stratum 3. The GFP-expressing cells in the GCL resemble the type B1, or possibly A2 ganglion cells. The CD44-EGFP mice should provide a valuable resource for electrophysiological and connectivity studies of amacrine cells in the mouse retina.

Amacrine Cells↗

PubMed2005

Production, purification, and characterization of human scFv antibodies expressed in Saccharomyces cerevisiae, Pichia pastoris, and Escherichia coli.

Single chain (scFv) antibodies are used as affinity reagents for diagnostics, therapeutics, and proteomic analyses. The antibody discovery platform we use to identify novel antigen binders involves discovery, characterization, and production. The discovery and characterization components have previously been characterized but in order to fully utilize the capabilities of affinity reagents from our yeast surface display library, efforts were focused on developing a production component to obtain purified, soluble, and active scFvs. Instead of optimizing conditions to achieve maximum yield, efforts were focused on using a system that could quickly and easily produce and process hundreds of scFv antibodies. Heterologous protein expression in Saccharomyces cerevisiae, Pichia pastoris, and Escherichia coli were evaluated for their ability to rapidly, efficaciously, and consistently produce scFv antibodies for use in downstream proteomic applications. Following purification, the binding activity of several scFv antibodies were quantified using a novel Biacore assay. All three systems produced soluble scFv antibodies which ranged in activity from 0 to 99%. scFv antibody yields from Saccharomyces, Pichia, and E. coli were 1.5-4.2, 0.4-7.3, and 0.63-16.4 mgL(-1) culture, respectively. For our purposes, expression in E. coli proved to be the quickest and most consistent way to obtain and characterize purified scFv for downstream applications. The E. coli expression system was subsequently used to study three scFv variants engineered to determine structure-function relationships.

Cloning, Molecular↗

PubMed2006

Physico-chemical and biological characterizations of two human prolactin analogs exhibiting controversial bioactivity, synthesized in Chinese hamster ovary (CHO) cells.

The synthesis, purification and characterization of G129R-hPRL and S179D-hPRL, the two better-studied antagonists of human prolactin (hPRL), is described. Both of these have been expressed for the first time, in their authentic form, by a stable CHO cell line, at secretion levels of 7.7 and 4.3 microg/10(6) cells/day, respectively. Previous studies had shown that these hPRL analogs, when produced in bacterial cytoplasm, consistently contained misfolded forms and multimers according to the specific denaturation, refolding and purification conditions. These versions also have an N-terminal extra methionine. An extensive physico-chemical characterization was carried out after a practical two-step purification process and included SDS-PAGE and Western blotting analysis, matrix-assisted laser-desorption ionization time-of-flight mass spectral (MALDI-TOF-MS) analysis, high-performance size-exclusion chromatography (HPSEC) and reversed-phase high-performance liquid chromatography (RP-HPLC). This last technique revealed a considerable difference in hydrophobicity due to a single amino acid substitution, with S179D-hPRL less (t(RR) = 0.85 +/- 0.010) and G129R-hPRL more (t(RR) = 1.10 +/- 0.013) hydrophobic than hPRL, where t(RR) is the relative retention time. The biological characterization was based on further refinement of a sensitive proliferation assay using the pro-B murine cell line (Ba/F3) transfected with the long form hPRL receptor cDNA such that the minimal detectable dose was 0.04 ng of hPRL/mL, the Ba/F3-LLP assay. On the basis of this assay, the relative residual agonistic activity of these two products, determined against a hPRL international standard in four independent assays, was 53 x 10(-3) for S179D-hPRL and 70 x 10(-5) for G129R-hPRL. We believe that the present synthesis and characterization could be extremely helpful for studies of these two proteins, which have been reported to antagonize tumor growth-promoting effects of hPRL in vivo in animal models of breast and prostate cancer.

Animals↗

PubMed2006

Biochemical characterization of rhEpo-Fc fusion protein expressed in CHO cells.

One challenge in biotechnology industry is to produce recombinant proteins with prolonged serum half-life. One strategy for enhancing the serum half-life of proteins includes increasing the molecular weight of the protein of interest by fusion to the Fc part of an antibody. In this context, we have expressed a homodimer fusion protein in CHO cells which consists of two identical polypeptide chains, in which our target protein, recombinant human erythropoietin (rhEpo), is N-terminally linked with the Fc part of a human IgG(1) molecule. In the present study, culture supernatant of a stable clone was collected and purified by affinity chromatography prior characterization. We emphasized product quality aspects regarding the fusion protein itself and in addition, post-translational characterization of the subunits in comparison to human antibodies and rhEpo. However, overproduction of recombinant proteins in mammalian cells is well established, analysis of product quality of complex products for different purposes, such as product specification, purification issues, batch to batch consistency and therapeutical consequences, is required. Besides product quantification by ELISA, N-acetylneuraminic acid quantification in microtiterplates, quantitative isoform pattern and entire glycan profiling was performed. By using these techniques for the characterization of the recombinant human Epo-Fc (rhEpo-Fc) molecule itself and furthermore, for the separate characterization of both subunits, we could clearly show that no significant differences in the core glycan structures compared to rhEpo and human antibody N-glycans were found. The direct comparison with other rhEpo-Fc fusion proteins failed, because no appropriate data were found in the literature.

Animals↗

PubMed2005

Isolation, molecular characterization and antimicrobial resistance patterns of Salmonella and Escherichia coli isolates from meat-based fast food in Lebanon.

The aim of this study was to characterize at the molecular level the different stains of Salmonella spp. and Escherichia coli that were isolated from meat-based fast food in Lebanon. In addition, this study evaluated the resistance of those strains to different antimicrobials that are commonly used. The foods included were Lahm-bi-Ajeen (LBA, meat pies) and Shawarma (Lebanese meat sandwiches similar to Gyros and Donairs, containing meat, vegetables, and sesame seeds-oil-based sauce). Polymerase chain reaction (PCR) was used to characterize and identify the strains of both bacteria. Salmonella species characterization was performed using rfb genes cluster genetic marker, while that of E. coli strains were carried out based on stx1, stx2, eaeA, fliC, and ehlyA virulence markers. The characterized strains were then tested for their response to various antimicrobials. The results showed that the tested foods were contaminated with Salmonella paratyphi (serogroup A) and Shiga Toxin (Stx)-producing E. coli (STX-EC). The PCR showed that 75% of E. coli tested strains was positive in PCR performed with stx1 primers, one of which was eaeA positive. Two of the tested strains were positive using PCR with fliC primers. The resistances of the various strains were evaluated using the following antimicrobials: Oxacillin, Teicoplanin, Trimethoprim/sulfamethoxazole, Gentamicin, Clindamycin, Cefotaxime, Cefuroxime, Erythromycin, and Vancomycin. Bacteria were highly resistant to one or more of the tested antimicrobials. Approximately 69% of E. coli and 77.8% of Salmonella spp. exhibited resistance. Salmonella spp. were shown to be 100% resistant to four antimicrobials: Oxacillin, Teicoplanin, Clindamycin, Vancomycin, and Erythromycin, while E. coli was 100% resistant to Teicoplanin and Trimethoprim/sulfamethoxazole. The most interesting findings were the high susceptibility of the E. coli to Gentamicin (100%). Highest resistance in the case of Salmonella spp. was seen against Cefotaxime (74%). Those two antimicrobials are commonly used for the treatment of enteric infections caused by gram-negative bacteria. The results showed that meat-based fast foods in Lebanon could be a public health hazard, especially Shawarma, as they may act as a potential vehicle for many antimicrobial-resistant pathogenic organisms. Improper hygienic standards and indiscriminate use of antimicrobials are two of the main causes for the prevalence of these pathogenic resistance strains in Lebanon. These results will emphasize the need to implement protective measures and more emphasis will be placed on the application of hygienic practices to reduce the levels of food contamination.

Anti-Bacterial Agents↗

PubMed2002

Molecular brightness characterization of EGFP in vivo by fluorescence fluctuation spectroscopy.

We characterize the molecular properties of autofluorescence and transiently expressed EGFP in the nucleus and in the cytoplasm of HeLa cells by fluorescence correlation spectroscopy (FCS) and by photon counting histogram (PCH) analysis. PCH has been characterized and applied in vitro, but its potential for in vivo studies needs to be explored. Thus, this study mainly focuses on the characterization of PCH analysis in vivo. The strength of PCH lies in its ability to distinguish biomolecules by their molecular brightness value. Because the concept of molecular brightness is crucial for PCH analysis, we study the molecular brightness of EGFP and determine the statistical accuracy of its measurement under in vivo conditions. We started by characterizing the influence of autofluorescence on EGFP measurements. We found a molecular brightness of EGFP that is a factor of 10 higher than the brightness of the autofluorescence. Moment analysis demonstrates that the contribution of autofluorescence to fluorescence fluctuation experiments is negligible at EGFP concentrations of one protein per excitation volume. The molecular brightness of EGFP measured in the nucleus, the cytoplasm, and in vitro are identical and our study demonstrates that molecular brightness is a very stable and predictable quantity for cellular measurements. In addition to PCH, we also analyzed the autocorrelation function of EGFP. The diffusion coefficient of EGFP is a factor of 3 lower in vivo than compared to in vitro, and a simple diffusion process describes the autocorrelation function. We found that in the nucleus the fluorescence intensity is stable as a function of time, while measurements in the cytoplasm display fluorescence intensity drifts that complicate the data analysis. We introduce and discuss an analysis method that minimizes the influence of the intensity drifts on PCH analysis. This method allows us to recover the correct molecular brightness of EGFP even in the presence of drifts of the fluorescence intensity signal. We found the molecular brightness of EGFP to be a very robust parameter, and anticipate the use of PCH analysis for the study of oligomerization processes in vivo.

Cell Nucleus↗

PubMed2002

Solute-solvent interactions in micellar electrokinetic chromatography. III. Characterization of the selectivity of micellar electrokinetic chromatography systems.

Several micellar electrokinetic chromatography (MEKC) systems (sodium dodecyl sulfate, lithium dodecyl sulfate, lithium perfluorooctanesulfonate, sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide) have been characterized by means of the solvation parameter model. It has been observed that the coefficients of the correlation equations depend strongly on the particular set of compounds analyzed. Principal component analysis has been used to characterize the 2975 compounds with available solute descriptors and to select an appropriate subset of compounds to be analyzed by MEKC. With this set of compounds, the MEKC systems have been characterized. Principal component analysis has also been used to show the similarities and differences between the properties of the surfactants characterized by MEKC.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2003

Energetics of lesion recognition by a DNA repair protein: thermodynamic characterization of formamidopyrimidine-glycosylase (Fpg) interactions with damaged DNA duplexes.

As part of an overall effort to map the energetic landscape of the base excision repair pathway, we report the first thermodynamic characterization of repair enzyme binding to lesion-containing duplexes. Isothermal titration calorimetry (ITC) in conjunction with spectroscopic measurements and protease protection assays have been employed to characterize the binding of Escherichia coli formamidopyrimidine-glycosylase (Fpg), a bifunctional repair enzyme, to a series of 13-mer DNA duplexes. To resolve energetically the binding and the catalytic events, several of these duplexes are constructed with non-hydrolyzable lesion analogs that mimic the natural 8-oxo-dG substrate and the abasic-like intermediates. Specifically, one of the duplexes contains a central, non-hydrolyzable, tetrahydrofuran (THF) abasic site analog, while another duplex contains a central, carbocyclic substrate analog (carba-8-oxo-dG). ITC-binding studies conducted between 5.0 degrees C and 15.0 degrees C reveal that Fpg association with the THF-containing duplex is characterized by binding free energies that are relatively invariant to temperature (deltaG approximately -9.5 kcalmol(-1)), in contrast to both the reaction enthalpy and entropy that are strongly temperature-dependent. Complex formation between Fpg and the THF-containing duplex at 15 degrees C exhibits an unfavorable association enthalpy (deltaH=+7.5 kcalmol(-1)) that is compensated by a favorable association entropy (TdeltaS=+17.0 kcalmol(-1)). The entropic nature of the binding interaction, coupled with the large negative heat capacity (deltaC(p)=-0.67 kcaldeg(-1)mol(-1)), is consistent with Fpg complexation to the THF-containing duplex involving significant burial of non-polar surface areas. By contrast, under the high ionic strength buffer conditions employed herein (200 mM NaCl), no appreciable Fpg affinity for the carba-8-oxo-dG substrate analog is detected. Our results suggest that initial Fpg recognition of a damaged DNA site is predominantly electrostatic in nature, and does not involve large contact interfaces. Subsequent base excision presumably facilitates accommodation of the resulting lesion site into the binding pocket, as the enzyme interaction with the THF-containing duplex is characterized by high affinity and a large negative heat capacity change. Our data are consistent with a pathway in which Fpg glycosylase activity renders the base excision product a preferred ligand relative to the natural substrate, thereby ensuring the fidelity of removing highly reactive and potentially mutagenic abasic-like intermediates through catalytic elimination reactions.

Base Sequence↗

PubMed1992

The detection and characterization of vesicoureteral reflux in the child.

Voiding cystourethrography or radionuclide cystography should be performed in the child in whom it is important to know whether reflux is present. Voiding cystourethrography is more accurate in characterizing and grading reflux, and monitoring is intermittent. Conversely, radionuclide cystography uses a lower radiation dose and its continuous monitoring leads to fewer false negative results but its ability to characterize reflux is poor. The performance of voiding cystourethrography or radionuclide cystography to detect reflux is an art as well as a science. These tests are done best by those who are experienced and interested in imaging the urinary tract of the child. At our hospital we perform voiding cystourethrography in all young children with urinary tract infection to detect and precisely characterize reflux to enable intelligent planning of management. In older patients, when it is less likely that reflux is present but it is still desirable to ensure that reflux is not occurring, radionuclide cystography is performed. If reflux is present, then a decision is made on an individual basis as to whether additional characterization by voiding cystourethrography is needed. Radionuclide cystography is also used for family screening, for periodic followup of reflux being managed nonoperatively and to ensure that reflux has been eliminated after antireflux surgery.

Child↗

PubMedDate not supplied

The polymerase chain reaction (PCR) in the routine genetic characterization of retinoblastoma: a tool for the clinical laboratory.

The Polymerase Chain Reaction (PCR) is a highly innovative technique which allows for the generation of large amounts of DNA starting from minute quantities obtained from the blood or tissue of a patient. With the increasing knowledge concerning the structure of the human genome and the potential to amplify specific segments of DNA by the PCR technique, the molecular genetic characterization of many ocular disorders has been greatly facilitated. This is particularly true of retinoblastoma (RB) where the causative gene, RB1, gene has been identified and characterized. Using PCR technique, specific sequences of the RB1 gene can be amplified and analyzed to precisely define the genetic mutation in an affected individual. In addition, this technique can also be applied in order to characterize the genetic defect within the tumor itself. In this report we illustrate the use of the PCR technique in the genetic characterization of the RB1 gene and its application to the study of RB. These techniques are applicable even in a small clinical laboratory and can be extended to a number of ophthalmic disorders.

Chromosome Mapping↗

PubMed2002

Surface waves investigation for ultrasonic materials characterization: theory and experimental verification.

Surface waves are increasingly attractive for ultrasonic NDE of high technology materials. In previous works, the characterization of viscoelastic and metallic plates has been carried out when geometrical laws of acoustics apply. It has been seen that the accuracy of a material characterization depends strongly on the redundancy of the information of the ultrasonic beam in this material. Good accuracy can be achieved if multiple pulses propagate through the plates. This conclusion may be very useful if one tries to characterize a material when non-geometrical laws of acoustics take place giving birth to leaky surface waves propagation. The aim of this work is to study the different possible generated surface leaky waves in materials. These waves are used for retrieving the acoustic parameters of the device under test. A theoretical model based on the complex harmonic waves combination is used. This model has already been developed for material characterization under normal conditions and is extended here to cover the description of the non-specular effects. The acoustic properties of the material are retrieved by inversion based on applying a consistent estimator on the experimental measurements and the developed model.

Journal Article↗

PubMed2003

Characterization of piezoelectric materials with large piezoelectric and electromechanical coupling coefficients.

The relaxor based ferroelectric (1-x)Pb(Zn(1/3)Nb(2/3))O(3)-xPbTiO(3) and (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) single crystals provided new challenges in property characterization because their extraordinarily large piezoelectric coefficients and electromechanical coupling coefficients. Large errors may occur in some of the derived material constants using conventional characterization techniques. This paper will analyze the inadequacy of the traditional characterization methods and provide some basic guidelines for properly characterizing piezoelectric materials with extremely high piezoelectric and electromechanical coupling coefficients.

Crystallography↗

PubMed1998

Isolation and characterization of a novel 98-kd Dermatophagoides farinae mite allergen.

BACKGROUND: Exposure to allergens from house dust mites is a significant cause of immediate hypersensitivity. Thus far, the active mite allergens defined are low molecular weight (MW) proteins or glycoproteins. However, other important mite allergens remain to be investigated. In this study a high MW mite antigen with a high IgE-binding activity was characterized. METHODS: An anti-Dermatophagoides farinae (Df) monoclonal antibody, mAb642, which recognized a 98-kd allergenic mite protein, was used for affinity chromatography. The purified Df642 was characterized biochemically and immunologically. RESULTS: Competitive ELISA demonstrated that mAb642 was inhibited by the interaction between serum IgE from allergic patients and Df642 antigen in a dose-dependent fashion. The IgE reactivity to both 98-kd and 92-kd components was removed or diminished by preincubation of asthmatic sera with Df642-coated CNBr-activated cellulose-4B gel. Two-dimensional immunoblot analysis revealed that there are at least 4 isoforms of Df642 that represent a minor component in the crude mite extract. The allergenicity of Df642 was assayed by IgE immunoassay with a large panel of 67 sera from asthmatic patients with positive skin reactions, and Df 642 showed positive IgE reactivity with more than 80% of the sera tested. Thus it should be classified as an important allergen. In addition, amino acid sequence analysis revealed that Df642 shares more than 50% homology with paramyosin from invertebrates. CONCLUSION: We have identified and characterized a 98-kd house dust mite allergen that showed greater than 80% IgE reactivity with sera from patients allergic to mites. This is the first high MW allergen characterized to date, and it shares high sequence homology with paramyosins in invertebrates.

Adolescent↗