bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion barrier properties of tungsten nitride films grown by atomic layer deposition from bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia
Authors: Becker Jill S. , Gordon Roy G.
Published: April 2003

Highly uniform, smooth, and conformal coatings of tungsten nitride (WN) were synthesized by atomic layer deposition (ALD) from vapors of bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia. The films are shiny, silver colored, and electrically conducting. The films were amorphous as deposited. 100% step coverage was obtained inside holes with aspect ratios greater than 40:1. WN films as thin as 1.5 nm proved to be good barriers to diffusion of copper for temperatures up to 600 °C. Annealing for 30 min at temperatures above 725 °C converted the WN to pure, polycrystalline tungsten metal. ALD of copper onto the surface of the WN produced strongly adherent copper films that could be used as “seed” layers for chemical vapor deposition or electrodeposition of thicker copper coatings.
Single quantum dot spectroscopy of CdSe/ZnSe grown on vicinal GaAs substrates
Authors: Makino T. , André R. , Gérard J.-M. , Romestain R. , Dang Le Si , Bartels M. , Lischka K. , Schikora D.
Published: April 2003

We investigated the optical properties of two monolayers of CdSe sandwiched by ZnSe layers grown by molecular-beam epitaxy on GaAs substrates with a vicinal tilt of 2° in the [111] direction. By varying the spatial resolution from 10 μm down to 500 nm, sharp photoluminescence lines due to the recombination of excitons confined into quantum dots could be observed at low temperature. The dot density could be as low as ≈109 dots/cm2, which is smaller than previously reported values by at least one order of magnitude.
Electron states in boron nitride nanocones
Authors: Azevedo Sérgio , Mazzoni Mário S. C. , Chacham H. , Nunes R. W.
Published: April 2003

We apply first-principles calculations to study the electronic structure of boron nitride nanocones with disclinations of different angles θ=nπ/3. Nanocones with odd values of n present antiphase boundaries that cause a reduction of the work function of the nanocones, relative to the bulk BN value, by as much as 2 eV. In contrast, nanocones with even values of n do not have such defects and present work functions that are very similar to the BN bulk value. These results should have strong consequences for the field emission properties of boron nitride nanocones and nanotubes.
High temperature electrical properties of highly epitaxial CaCu3Ti4O12 thin films on (001) LaAlO3
Authors: Chen L. , Chen C. L. , Lin Y. , Chen Y. B. , Chen X. H. , Bontchev R. P. , Park C. Y. , Jacobson A. J.
Published: April 2003

The high temperature electrical behavior of highly epitaxial CaCu3Ti4O12 thin films on (001) LaAlO3 have been systematically investigated with traditional four-probe dc and ac resistance measurement techniques and two-probe ac impedance spectroscopy. Both ac and dc resistance measurements reveal that the Arrhenius plot, ln(σ) vs (1/T), forms two linear sections with a transition temperature between them at 773 K, one with the activation energy Ea of ∼1.3 eV at low temperature, and the other with the activation energy Eb of ∼0.5 eV at high temperatures. The high temperature impedance spectra also confirm these phenomena and suggest that unlike in polycrystalline bulk material, the high frequency response is predominantly from grains rather than grain boundaries.
Green, blue, and yellow cathodoluminescence of Ba2B5O9Cl thin-films doped with Tb3+, Tm3+, and Mn2+
Authors: Hao Jianhua , Gao J. , Cocivera Michael
Published: April 2003

Green, blue, and yellow cathodoluminescence (CL) have been obtained for thin-films of Ba2B5O9Cl doped with Tb3+, Tm3+, and Mn2+, respectively. These phosphor films were deposited by spray pyrolysis, and then activated in air at temperatures suitable for use on glass substrates. The CL characteristic peaks of the films correspond to transitions between electronic energy levels of Tm3+, Tb3+, and Mn2+ ions. The chromaticity coordinates, dominant wavelength, and color purity were determined for each phosphor. Saturation effects were observed as the beam current density increased. The more severe current saturation of Mn-doped film may be due to a greater ground state deplection of Mn luminescent centers than that of the Tb and Tm.
Magnesium incorporation at (0001) inversion domain boundaries in GaN
Authors: Northrup John E.
Published: April 2003

First-principles pseudopotential density functional calculations have been performed for Mg-rich inversion domain boundaries that form on (0001) planes in GaN. These types of boundaries separate inverted material from the host matrix in the pyramidal inversion domain defects reported to exist in heavily Mg-doped GaN. The model of the boundary proposed on the basis of these total energy calculations exhibits GaNMgNGa layers that are stacked in abcab registry, with at least 3/4 of the available c sites occupied by Mg atoms. An additional 1/4 monolayer of Mg can be incorporated in this layer provided additional compensating Mg acceptors are located nearby. A significant fraction of the Mg present in heavily doped material may reside in these boundaries.
Conductance measurement of single-walled carbon nanotubes in aqueous environment
Authors: Someya Takao , Kim Philip , Nuckolls Colin
Published: April 2003

We report measurement of conductance of single-walled carbon nanotubes in aqueous media using a field effect geometry in which source and drain electrodes are protected with a photopolymerized epoxy. Without this protection, exposure to aqueous media degrades the device instantly. The 2.6 μm width open slits are prepared by photolithography at the central region between source and drain electrodes, whose spacing, or channel length, is 5 μm, so that only the nanotube channel can be directly exposed to an aqueous environment, while the metal–nanotube junctions are protected. For protected devices, the response to water as characterized primarily by changes in threshold voltage is reversible and reproducible.
Ferromagnetic resonant interband tunneling diode
Authors: Vurgaftman I. , Meyer J. R.
Published: April 2003

We consider the spin-polarizing properties of a ferromagnetic resonant interband tunneling diode based on the type-II InAs/(AlSb)/GaMnSb/(AlSb)/InAs heterostructure system. The current–voltage characteristics are simulated using the effective bond-orbital method, in conjunction with self-consistent treatments of both the electrostatic potential and the magnetic exchange interaction. We find that the device can be employed as either a source of spin-polarized electrons, whose polarity varies with applied bias, or as a spin valve. For example, the polarization of electrons tunneling to the collector from an unpolarized emitter can exceed 75% in either direction.
Pressure-induced phase of NaAlH4: A potential candidate for hydrogen storage?
Authors: Vajeeston P. , Ravindran P. , Vidya R. , Fjellvåg H. , Kjekshus A.
Published: April 2003

The electronic structure and structural stability of the technologically interesting material NaAlH4 are studied using an ab initio projected augmented plane-wave method for different possible structure modifications. We predict that α-NaAlH4 converts to β-NaAlH4 at 6.43 GPa with a 4 % volume contraction. Both modifications have nonmetallic character with finite energy gaps, the calculated band gap for β-NaAlH4 being almost half of that for the α phase. β-NaAlH4 stores hydrogen more volume efficient than the α phase and would if stabilized at ambient conditions be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency.
Effect of annealing on carrier density and Curie temperature in epitaxial (Ga,Mn)As thin films
Authors: Sørensen B. S. , Lindelof P. E. , Sadowski J. , Mathieu R. , Svedlindh P.
Published: April 2003

We report a clear correspondence between changes in the Curie temperature and carrier density upon annealing in epitaxially grown (Ga,Mn)As layers with thicknesses in the range between 5 and 20 nm. The changes are dependent on the layer thickness, indicating that the (Ga,Mn)As–GaAs interface has importance for the physical properties of the (Ga,Mn)As layer. The magnetoresistance shows additional features when compared to thick (Ga,Mn)As layers, that are at present of unknown origin.
Optical cavity effects in InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes
Authors: Shen Y. C. , Wierer J. J. , Krames M. R. , Ludowise M. J. , Misra M. S. , Ahmed F. , Kim A. Y. , Mueller G. O. , Bhat J. C. , Stockman S. A. , Martin P. S.
Published: April 2003

Optical cavity effects have a significant influence on the extraction efficiency of InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes (FCLEDs). Light emitted from the quantum well (QW) self-interferes due to reflection from a closely placed reflective metallic mirror. The interference patterns couple into the escape cone for light extraction from the FCLED. This effect causes significant changes in the extraction efficiency as the distance between the QW and the metallic mirror varies. In addition, the radiative lifetime of the QW also changes as a function of the distance between the QW and the mirror surface. Experimental results from packaged FCLEDs, supported by optical modeling, show that a QW placed at an optimum distance from the mirror provides a ∼2.3× increase in total light output as compared to a QW placed at a neighboring position corresponding to a minimum in overall light extraction.
Determination of the composition of lithium tantalate crystals by zero-birefringence measurements
Authors: Bäumer Ch. , Berben D. , Buse K. , Hesse H. , Imbrock J.
Published: April 2003

We present an approach to determine the exact composition of lithium tantalate (LiTaO3) crystals by measuring the temperature where the birefringence disappears. Various samples with compositions ranging from the congruently melting to the stoichiometric one have been prepared by vapor transport equilibration treatments and are investigated. The sensitivity is as high as 1.5 °C/0.01 mol % Li2O. The relative accuracy is better than 0.01 mol %, while the absolute accuracy is limited by the calibration.
Physical basis of fragility
Authors: Bendler J. T. , Fontanella J. J. , Shlesinger M. F.
Published: April 2003

Fragility of glass-forming liquids in the supercooled region is considered in the context of a defect diffusion theory. It is shown that a necessary condition that a liquid be “fragile” is that there is an attractive interaction between the mobile defects, i.e., that the defects cluster with falling temperature. The relationship between the model parameters and a widely used fragility index is described. Each of the model parameters provides a contribution to and insight into the fragility value. The behavior of exceptional cases, such as orientationally disordered crystals and aliphatic monohydric alcohols, is also naturally accounted for in terms of the model.
Mechanism for ultrafast internal conversion of adenine
Authors: Kang Hyuk , Jung Boyong , Kim Seong Keun
Published: April 2003

The mechanism for the internal conversion of adenine was investigated by femtosecond pump–probe transient ionization time-of-flight mass spectrometry. In particular, we tried to determine which of the nπ* and πσ* states was responsible for the ultrafast decay of adenine by comparing the dynamics of adenine and its several derivatives with methyl or deuterium substitution. Adenine and all its derivatives studied here had more or less the same decay time of ∼1 ps at the excitation energy of 37 500 cm−1. These results provide compelling evidence that the nπ* state, rather than the πσ* state, plays the role of a doorway state for internal conversion via a conical intersection to the ground state.
Negative temperature coefficient thermistor based on Bi3Zn2Sb3O14 ceramic: An oxide semiconductor at high temperature
Authors: Nobre M. A. L. , Lanfredi S.
Published: April 2003

Bi 1.5 ZnSb 1.5 O 7 dielectric ceramic with pyrochlore structure was investigated by impedance spectroscopy from 400 to 750 °C. Pyrochlore was synthesized by the polymeric precursor method, a chemical synthesis route derived from Pechini’s method. The grain or bulk resistance exhibits a sensor temperature characteristic, being a thermistor with a negative temperature coefficient (NTC). Only a single region was identified on the resistance curve investigated. The NTC thermistor characteristic parameter (β) is equal to 7140 °C, in the temperature range investigated. The temperature coefficient of the resistance (α) was derived, being equal to −4.46×10−2 °C−1 at 400 °C. The conduction mechanism and relaxation are discussed.
High-speed solar-blind photodetectors with indium-tin-oxide Schottky contacts
Authors: Biyikli Necmi , Kimukin Ibrahim , Kartaloglu Tolga , Aytur Orhan , Ozbay Ekmel
Published: April 2003

We report AlGaN/GaN-based high-speed solar-blind photodetectors with indium-tin-oxide Schottky contacts. Current–voltage, spectral responsivity, and high-frequency response characterizations were performed on the fabricated Schottky photodiodes. Low dark currents of <1 pA at 20 V reverse bias and breakdown voltages larger than 40 V were obtained. A maximum responsivity of 44 mA/W at 263 nm was measured, corresponding to an external quantum efficiency of 21%. True solar-blind detection was ensured with a cutoff wavelength of 274 nm. Time-based high-frequency measurements at 267 nm resulted in pulse responses with rise times and pulse-widths as short as 13 and 190 ps, respectively. The corresponding 3-dB bandwidth was calculated as 1.10 GHz.
Large magnetoresistance of bismuth/gold films thermally deposited onto glass substrates
Authors: Du Xu , Hebard A. F.
Published: April 2003

Bismuth thin films deposited onto glass substrates by thermal sublimation are polycrystalline with short mean free paths, multiple grain orientations, and disappointingly small magnetoresistance when compared to single crystals. Direct deposition onto thin gold buffer layers followed by a post-deposition anneal leads to significantly improved properties, namely, large grains oriented in the trigonal direction and a 5-T magnetoresistance higher than 250% at room temperature. For a Bi0.93Au0.07 stoichiometry, we show that optimal results are obtained when the annealing temperature is above the BiAu eutectic point (241 °C) and below the melting temperature (271 °C) of bismuth, thus indicating a mechanism in which the presence of gold in the bismuth facilitates grain-boundary motion and grain growth.
Mercury cadmium telluride/tellurium intergrowths in HgCdTe epilayers grown by molecular-beam epitaxy
Authors: Aoki T. , Smith David J. , Chang Y. , Zhao J. , Badano G. , Grein C. , Sivananthan S.
Published: April 2003

Surface crater defects in HgCdTe epilayers grown by molecular-beam epitaxy have been investigated using cross-sectional scanning and transmission electron microscopy, as well as atomic force microscopy. These defects originated primarily within the HgCdTe films, and were shown to be associated with the local development of polycrystalline morphology. High-resolution observations established the occurrence of finely spaced HgCdTe/Te intergrowths with either semicoherent or incoherent grain boundaries, as well as small HgCdTe inclusions embedded within Te grains.
The effect of strain on tuning of light emission energy of InAs/InGaAs quantum-dot nanostructures
Authors: Seravalli L. , Minelli M. , Frigeri P. , Allegri P. , Avanzini V. , Franchi S.
Published: April 2003

We prepared by molecular-beam epitaxy and studied structures of InAs quantum dots embedded in InxGa1−xAs confining layers. The structures were designed so that the strain of quantum dots could be controlled independently of In composition of confining layers. In such a way, we single out the effect of strain in quantum dots on the energy of photoluminescence emission. We show that strain can be effectively used to tune the emission energy of quantum dots, and that room-temperature emission at 1.3 μm can be obtained. Our results suggest that by quantum-dot strain engineering, it will be possible to extend emission wavelength beyond 1.55 μm.
Phosphorus and boron diffusion in silicon under equilibrium conditions
Authors: Christensen J. S. , Radamson H. H. , Kuznetsov A. Yu. , Svensson B. G.
Published: April 2003

The intrinsic diffusion of phosphorus and boron in high-purity epitaxial silicon films has been studied. Phosphorus diffusion in a wide temperature range (810 to 1100 °C) revealed diffusion coefficients with an Arrhenius behavior exhibiting an activation energy of 2.74±0.07 eV and a pre-exponential factor of (8±5)×10−4 cm2/s. In the temperature range of 810 to 1050 °C, boron was found to diffuse with an activation energy of 3.12±0.04 eV and a pre-exponential factor of 0.06±0.02 cm2/s. These results differ from those of many previous studies, but this deviation may to a large extent be attributed to slow transients before equilibrium concentrations of point defects are established at temperatures below ∼1000 °C. Despite a similar diffusion mechanism mediated by Si self-interstitials, P exhibits a lower activation energy than B because of stronger bonding to the Si self-interstitial.
In incorporation during the growth of quaternary III-nitride compounds by plasma-assisted molecular beam epitaxy
Authors: Monroy E. , Gogneau N. , Jalabert D. , Bellet-Amalric E. , Hori Y. , Enjalbert F. , Dang Le Si , Daudin B.
Published: April 2003

Epitaxial growth of quaternary AlGaInN compounds by plasma-assisted molecular beam epitaxy has been demonstrated. Two-dimensional growth is achieved under In excess, with an In film segregating at the growth front. The maximum In incorporation is significantly affected by the substrate temperature and the Al mole fraction of the alloy. This behavior has been attributed to the enhancement of In segregation due to the high binding energy of AlN compared to InN and GaN.
Field emission from a patterned organic conducting composite
Authors: Kymissis Ioannis , Akinwande Akintunde I.
Published: April 2003

We report a technique for forming nanopatterned films of organic conducting composites at room temperature. The devices are formed by copying a nonlithographically produced template to form a high-aspect-ratio volcano-like structure. Field emission was studied from these structures, and they were found to provide a field enhancement of about 250. The emission current was imaged on a phosphor screen and preliminary measurements were made of the response to gas exposure, demonstrating that air decreases the emissivity of these devices. This work demonstrates a straightforward room-temperature process for forming field emitters, a field-emitting material system with a conducting oxide, and preliminary evidence that air can degrade field emission through a purely dipolar interaction.
Unusual increase of the Auger recombination current in 1.3 μm GaInNAs quantum-well lasers under high pressure
Authors: Jin S. R. , Sweeney S. J. , Tomić S. , Adams A. R. , Riechert H.
Published: April 2003

The pressure dependence of the total threshold current and its respective recombination components in 1.3 μm GaInNAs single-quantum-well lasers using spontaneous emission measurements up to 13 kbar is presented. We observed an unusual increase of the nonradiative Auger recombination current with increasing pressure in this material, which is opposite to those in 1.3 μm InP-based InGaAsP and AlGaInAs devices where the Auger current decreases with pressure. It is shown that the high-pressure-induced increase of the threshold current in GaInNAs is associated with the increase of the Auger current, while the defect-related monomolecular nonradiative current remains nearly unchanged in the pressure range studied. Theoretical calculations show that the unusual increase of the Auger current with pressure in GaInNAs is due to a large increase in the threshold carrier density.
Electrical and interfacial characteristics of ultrathin ZrO2 gate dielectrics on strain compensated SiGeC/Si heterostructure
Authors: Mahapatra R. , Lee Je-Hun , Maikap S. , Kar G. S. , Dhar A. , Hwang Nong-M. , Kim Doh-Y. , Mathur B. K. , Ray S. K.
Published: April 2003

Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers by rf magnetron sputtering. High-resolution transmission electron microscopy along with energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy show the formation of a polycrystalline ZrO2 and an amorphous Zr–germano–silicate interfacial layer between the deposited oxide and SiGeC films. A dielectric constant of 17.5 for ZrO2 and 7.0 for an interfacial-silicate layer have been calculated from the high-frequency capacitance–voltage measurements. These dielectrics show an equivalent oxide thickness as low as 1.9 nm for ZrO2 and 2.0 nm for the interfacial silicate layer. An extremely low leakage current density of ∼9×10−8 A/cm2 at a gate voltage of −1.0 V, breakdown field of 7 MV/cm and moderate interface state density of 6×1011 cm−2 eV−1 have been obtained for the fabricated capacitors.
Intensity dependence and transient dynamics of donor–acceptor pair recombination in ZnO thin films grown on (001) silicon
Authors: Guo Bing , Qiu Z. R. , Wong K. S.
Published: April 2003

We report room-temperature time-integrated and time-resolved photoluminescence (PL) measurements on a nominally undoped wurtzite ZnO thin film grown on (001) silicon. A linear and sublinear excitation intensity Iex dependence of the PL intensity were observed for the 379.48-nm exciton line and the weak broad green band (∼510 nm), respectively. The green luminescence was found to decay as hyperbolic t−1, and its peak energy was observed to increase nearly logarithmically with increased Iex. These results are in an excellent agreement with the tunnel-assisted donor–deep-acceptor pair (DAP) model so that its large blueshifts of about 25 meV per decade increase in Iex can be accounted for by the screening of the fluctuating impurity potential. Also, the 30-ps fast decay of the exciton emission was attributed to the rapid trapping of carriers at luminescent impurities, while the short lifetime of τ1/e=200 ps for the green luminescence may be due to an alternative trapping by deeper centers in the ZnO. Finally, singly ionized oxygen and zinc vacancies have been tentatively invoked to act as donor–deep-acceptor candidates for the DAP luminescence, respectively.
Molecular analysis of VcfQ protein involved in Vibrio cholerae type IV pilus biogenesis
Authors: Miyazato Tomoko , Toma Claudia , Nakasone Noboru , Yamamoto Koichiro , Iwanaga Masaaki
Published: April 2003

The nucleotide sequence of an ORF (vcfQ) within the type IV pilus gene cluster of Vibrio cholerae O34 strain NAGV14 was determined, thereby completing the sequence analysis of the structural operon. The vcfQ gene showed homology to the mshQ gene of the mannose-sensitive haemagglutinin pilus gene cluster. The vcfQ was 651 bp larger than mshQ, and the G+C content of the extra 651 bp portion (35.6 mol%) was lower than that of the overall vcfQ gene (42.5 mol%). Except for the first 270 aa residues, the deduced amino acid sequence of VcfQ showed high homology to the MshQ protein. There was immunological cross-reaction between VcfQ and MshQ by Western blotting. Cell fractionation studies showed that VcfQ is located in both the inner and the outer membranes. Mutational analysis showed that vcfQ-deficient mutant expressed detectable levels of major pilin (VcfA), but failed to assemble them into pili, indicating that VcfQ is essential for pilus assembly. Colony-blotting analyses showed that the N-terminal region of vcfQ is variable in V. cholerae strains.
`Genotypic shuffling’ of sequential clones of Candida albicans in HIV-infected individuals with and without symptomatic oral candidiasis
Authors: Samaranayake Y.H. , Samaranayake L.P. , Dassanayake R.S. , Yau J.Y. Y. , Tsang W.K. , Cheung B.P. K. , Yeung K.W. S.
Published: April 2003

Although HIV-infected individuals harbour multiple strains of oral Candida albicans, little is known of their micro-evolution over time. Therefore, a prospective study was conducted with 16 HIV-infected ethnic Chinese individuals with and without symptoms of oropharyngeal candidiasis to evaluate the genotype distribution of oral C. albicans isolates during HIV disease progression. Oral-rinse samples were obtained from all individuals and up to five C. albicans colonies were selected for each visit, over a 12 month period of multiple visits. After identification of isolates using standard mycological criteria, the genetic similarities of yeast isolates within and between sequential clones of C. albicans were assessed by DNA fingerprinting through random amplification of polymorphic DNA (RAPD). The results of RAPD gel profiles and the lineage of each isolate were further analysed using commercially available software. RAPD studies revealed the prevalence of up to 14 different genotypes per individual during the study period, with multiple genotypes isolated simultaneously from a single oral rinse. Computer analysis of RAPD profiles revealed that yeasts isolated over sequential visits from symptomatic individuals demonstrated a striking level of relatedness compared with isolates from asymptomatic individuals. Genetically identical C. albicans strains also formed ‘loosely’ connected subclusters that overlapped multiple visits, implying genetic ‘shuffling’ in these isolates during disease progression. These data point to varying evolutionary genetic trends in C. albicans associated with symptomatic oral candidiasis and asymptomatic carriage in HIV disease.
Involvement of nitric oxide donor compounds in the bactericidal activity of human neutrophils in vitro
Authors: Klink Magdalena , Cedzyński Maciej , St Świerzko Anna , Tchórzewski Henryk , Sulowska Zofia
Published: April 2003

The bactericidal activity of human neutrophils against extracellular and facultatively intracellular bacteria was studied in the presence of the nitric oxide (NO) donors sodium nitroprusside (SNP) and 3-morpholinosydnonimine (SIN-1), a molsidomine metabolite. SNP and molsidomine are drugs commonly used as nitrovasodilators in coronary heart disease. It is demonstrated here that the NO donor compounds themselves did not affect the viability and survival of the bacterial strains tested. Neither SNP nor SIN-1 had any effect on the process of bacteria ingestion. In contrast, NO donors enhanced the ability of neutrophils to killEscherichia coli,Proteus vulgarisandSalmonellaAnatum. However, strains differed in their susceptibility to SNP- and SIN-1-mediated killing by neutrophils. Removal of the superoxide anion reduced the bactericidal activity of SNP- and SIN-1-treated neutrophils againstE. coliandS. Anatum. This suggests that the NO derivatives formed in the reaction of NO generated from donors with the reactive oxygen species released by phagocytosed neutrophils potentiate the bactericidal activity of human neutrophilsin vitro. The above original observation discussed here suggests clinical significance for the treatment of patients with nitrovasodilators in the course of coronary heart disease therapy.
Detection of Legionella DNA by PCR of whole-blood samples in a mouse model
Authors: Aoki S. , Hirakata Y. , Miyazaki Y. , Izumikawa K. , Yanagihara K. , Tomono K. , Yamada Y. , Tashiro T. , Kohno S. , Kamihira S.
Published: April 2003

A detection system for Legionella DNA in blood samples based on the PCR was developed and evaluated in A/J mice with experimentally induced Legionella pneumonia. Primers were designed to amplify a 106 bp DNA fragment of the 16S rRNA gene specific to Legionella species. The PCR system could detect clinically relevant Legionella species including Legionella pneumophila, Legionella micdadei, Legionella bozemanae, Legionella dumoffii, Legionella longbeachae, Legionella gormanii and Legionella jordanis. The sensitivity of the PCR system was 20 fg extracted DNA. In the mouse model, the blood PCR was compared with results obtained by PCR on bronchoalveolar lavage fluid (BALF) samples, cultures of blood and BALF and detection of Legionella urinary antigen. Blood PCR was positive until 8 days after infection, while BALF PCR became negative on day 4. These results indicate that PCR using blood samples may be a useful, convenient and non-invasive method for the diagnosis of Legionella pneumonia.
Specific PCR detection of Peptostreptococcus magnus
Authors: Riggio M.P. , Lennon A.
Published: April 2003

Peptostreptococcus magnusis the most pathogenic and one of the most common Gram-positive anaerobic cocci found in human clinical specimens. The organism has been isolated in pure culture from a range of serious infections, including meningitis and endocarditis. However, isolation ofPeptostreptococcus magnusfrom the oral cavity has rarely been attempted. Identification ofPeptostreptococcus magnusin clinical specimens is reliant upon microbiological culture and biochemical methods, which often give ambiguous results. The aim of this study was to develop a PCR assay for the specific detection ofPeptostreptococcus magnusin oral clinical specimens. PCR primers specific forPeptostreptococcus magnusDNA were derived by comparison of 16S rRNA gene sequences and selection of primers that demonstrated specificity at their 3′ ends forPeptostreptococcus magnus. PCR positivity forPeptostreptococcus magnusDNA was indicated by the amplification of a 553 bp product. The PCR assay was then used to attempt detection ofPeptostreptococcus magnusDNA in subgingival plaque samples from adult periodontitis patients and pus aspirates from subjects with acute dento-alveolar abscesses. The PCR assay was demonstrated to be highly specific forPeptostreptococcus magnusDNA, since no PCR products were obtained when genomic DNA from a wide range of other oral bacteria, including closely relatedPeptostreptococcusspecies, was used in the PCR assay. Confirmation of specific amplification ofPeptostreptococcus magnusDNA was obtained by digestion of PCR products with the restriction endonucleaseRsaI, which gives a unique restriction profile forPeptostreptococcus magnus. Of the 33 subgingival plaque samples analysed, 2 (6 %) were positive forPeptostreptococcus magnusDNA. None of the 60 pus aspirates analysed was positive forPeptostreptococcus magnusDNA. It is concluded thatPeptostreptococcus magnusis not a major pathogen in adult periodontitis or dento-alveolar abscesses. The PCR assay provides a more rapid, specific and sensitive alternative to conventional methods for identification ofPeptostreptococcus magnusin clinical specimens.
Haemophilus influenzae Rd KW20 has virulence properties
Authors: Daines Dayle A. , Cohn Leah A. , Coleman Hannah N. , Kim Kwang Sik , Smith Arnold L.
Published: April 2003

Haemophilus influenzae is a human-adapted commensal and pathogen that can cause mucosal infections such as sinusitis, otitis media and bronchitis. Certain strains also cause bacteraemia and meningitis. Clinical isolates are genetically heterogeneous and are often recalcitrant to standard genetic manipulation. H. influenzae strain Rd KW20 has traditionally been considered avirulent, since it does not survive in the bloodstream of animals, is readily killed by normal adult human sera and cannot colonize the nasopharynx of infant rats. The purpose of this study was to determine whether Rd KW20 could be used in certain infection models. It is shown here that strain Rd KW20 can invade certain human epithelial cell lines grown either as monolayers or as differentiated epithelium at the air–liquid interface. In addition, Rd KW20 can invade a monolayer of immortalized human brain microvascular endothelial cells. Finally, this strain can replicate and survive in human bronchial xenografts for up to 3 weeks. The complete genomic sequence of Rd KW20 is available and it is readily amenable to genetic manipulation. These properties and the results reported here indicate that this strain is a viable alternative to the use of clinical isolates for the investigation of H. influenzae virulence.
Molecular analysis of the microflora in chronic venous leg ulceration
Authors: Hill K.E. , Davies C.E. , Wilson M.J. , Stephens P. , Harding K.G. , Thomas D.W.
Published: April 2003

There is growing evidence to suggest that the resident microflora of chronic venous leg ulcers impairs cellular wound-healing responses, thereby playing an important role in maintaining the non-healing phenotype of many of these wounds. The significance of individual species of bacteria will remain unclear until it is possible to characterize fully the microflora of such lesions. The limitations and biases of culture-based microbiology are being realized and the subsequent application of molecular methods is revealing greater diversity within mixed bacterial populations than that demonstrated by culture alone. To date, this approach has been limited to a small number of systems, including the oral microflora. Here, for the first time, the comprehensive characterization of the microflora present in the tissue of a chronic venous leg ulcer is described by the comparison of 16S rDNA sequences amplified directly from the wound tissue with sequences obtained from bacteria that were isolated by culture. The molecular approach demonstrated significantly greater bacterial diversity than that revealed by culture. Furthermore, sequences were retrieved that may possibly represent novel species of bacteria. It is only by the comprehensive analysis of the wound microflora by both molecular and cultural methods that it will be possible to further our understanding of the role of bacteria in this important condition.
Experimental infection of layer hens with a human isolate of Brachyspira pilosicoli
Authors: Jamshidi Abdollah , Hampson David J.
Published: April 2003

The anaerobic intestinal spirochaete Brachyspira pilosicoli commonly colonizes the large intestine of a number of species, including chickens and human beings. The purpose of the current study was to determine whether an isolate of B. pilosicoli recovered from an HIV-infected patient with diarrhoea could infect and cause disease in adult chickens. Over a 4-week period following experimental infection, a group of eight inoculated chickens showed a persistent and significant increase in faecal water content (∼6–7 %). The faeces of three of the eight birds became culture-positive, and remained so. At post-mortem examination, no specific pathological changes were found, and no spirochaetal attachment to the caecal epithelium was observed. These findings confirm that B. pilosicoli strains can infect across species barriers and cause chronic mild diarrhoea in intact adult chickens.
Expression of heterologous O-antigen in Yersinia pestis KIM does not affect virulence by the intravenous route
Authors: Oyston P.C. F. , Prior J.L. , Kiljunen S. , Skurnik M. , Hill J. , Titball R.W.
Published: April 2003

All strains ofYersinia pestisexamined have been found to lack an O-antigen. In other members of theEnterobacteriaceae, the rough phenotype often results in attenuation. However,Y. pestisis the aetiological agent of bubonic plague. In evolving from the ancestral enteropathogenicYersinia pseudotuberculosis, and with the development of an arthropod-vectored systemic pathogenesis, smooth LPS production is not necessary forY. pestisvirulence and the metabolic burden has been alleviated by inactivation of the O-antigen biosynthetic operon. To investigate this,Y. pestisstrain KIM D27 was transformed with a plasmid carrying the operon encoding the O-antigen ofYersinia enterocoliticaO : 3. Expression of the O-antigen could be detected in silver-stained gels. The receptor for bacteriophage ϕYeO3-12 has been shown to be O-antigen, and infection by this bacteriophage results in lysis ofY. enterocoliticaO : 3. Expression of the O-antigen inY. pestisconferred sensitivity to lysis by ϕYeO3-12. The O-antigen-expressing clone was shown to be as virulent in mice by the intravenous route of challenge as the rough wild-type. Assays showed no alteration in the ability ofY. pestisto resist lysis by cationic antimicrobial peptides, serum or polymyxin.
Prevalence of 11 pathogenic genes of Campylobacter jejuni by PCR in strains isolated from humans, poultry meat and broiler and bovine faeces
Authors: Datta Suvamoy , Niwa Hidekazu , Itoh Kikuji
Published: April 2003

Although many genes related to the pathogenicity of Campylobacter jejuni have been reported, the relationships between these genes and the sources of strains are not clear. In this study, the presence of 11 pathogenic genes responsible for the expression of adherence, invasion, colonization and cytotoxin production was examined in 111 C. jejuni isolated from human clinical samples, poultry meat, broiler faeces and bovine faeces. For most of the pathogenic genes, no difference in their presence in C. jejuni was found among the sources, but, for racR, wlaN and virB11, there were some variations among sources. The racR gene was present at rates of 98.2 (human clinical samples), 90.5 (poultry meat), 85.7 (broiler faeces) and 76.7 % (bovine faeces). Detection rates for the wlaN gene were 25.0, 23.8, 4.7 and 7.7 % and those for the virB11 gene were 10.7, 9.5, 9.5 and 15.4 % in human clinical samples, poultry meat, broiler faeces and bovine faeces, respectively. One hundred and seven of 111 strains (96.4 %) carried from eight to 10 of the pathogenic genes. These data did not show remarkable differences in the presence of pathogenic genes carried by C. jejuni from various sources.
Towards a genotyping system for Streptococcus agalactiae (group B streptococcus): use of mobile genetic elements in Australasian invasive isolates
Authors: Kong Fanrong , Martin Diana , James Gregory , Gilbert Gwendolyn L.
Published: April 2003

This study forms part of the development of an integrated genotyping system forStreptococcus agalactiae(group B streptococcus, GBS) that can be used to study the population genetics of the organism and the pathogenesis and epidemiology of GBS disease. In recent previous studies, two sets of markers, the capsular polysaccharide synthesis (cps) gene cluster and surface protein antigen genes, have been used to assign molecular serotypes (MS) and protein-gene profiles (PGP) to more than 200 isolates. In the present study, five mobile genetic elements (MGE) have been used as a third set of markers, to characterize further 194 invasive isolates, recovered from blood or cerebrospinal fluid (CSF). Of these, 97 % contained one or more of the five MGE, the distribution of which was related to MS and PGP, as illustrated by MS III, which is divisible into four serosubtypes with different combinations of the MGE (or none). Fifty-six different genotypes and eight genetic clusters were identified, each with different combinations of the three sets of molecular markers. Five predominant genotypes (Ia-1, Ib-1, III-1, III-2 and V-1) contained 62 % of the isolates and five of the eight genetic clusters contained 92 % of the isolates. The 17 CSF isolates were relatively widely distributed between 10 genotypes and across seven of the eight clusters. Further study is needed to determine whether these genotypes or clusters share common markers of increased virulence. In future, comparison of invasive with colonizing strains of GBS may elucidate the significance of these findings.
Highly adherent small-colony variants of Pseudomonas aeruginosa in cystic fibrosis lung infection
Authors: Häußler Susanne , Ziegler Isabell , Löttel Alexandra , Götz Franz v. , Rohde Manfred , Wehmhöhner Dirk , Saravanamuthu Selvan , Tümmler Burkhard , Steinmetz Ivo
Published: April 2003

Pseudomonas aeruginosa, an opportunistic human pathogen and ubiquitous environmental bacterium, is capable of forming specialized bacterial communities, referred to as biofilm. The results of this study demonstrate that the unique environment of the cystic fibrosis (CF) lung seems to select for a subgroup of autoaggregative and hyperpiliatedP. aeruginosasmall-colony variants (SCVs). These morphotypes showed increased fitness under stationary growth conditions in comparison with clonal wild-types and fast-growing revertants isolated from the SCV populationin vitro. In accordance with the SCVs being hyperpiliated, they exhibited increased twitching motility and capacity for biofilm formation. In addition, the SCVs attached strongly to the pneumocytic cell line A549. The emergence of these highly adherent SCVs within the CF lung might play a key role in the pathogenesis ofP. aeruginosalung infection, where a biofilm mode of growth is thought to be responsible for persistent infection.
Evaluation of a rapid bacteriophage-based method for the detection of Mycobacterium tuberculosis in clinical samples
Authors: Marei Ayman Mohamed , El-Behedy Eman Mohamed , Mohtady Heba Ali , Afify Afify Fahmy
Published: April 2003

Rapid, sensitive and low-cost methods are needed urgently for the detection of Mycobacterium tuberculosis in clinical samples, especially in developing countries. To this end, the clinical performance of FASTPlaqueTBTM (a bacteriophage-based method) has been studied in parallel with microscopy, standard microbiological culture and in-house IS6110-based PCR methods. A total of 64 samples, including 42 sputum samples and 22 urine samples, were tested in this study. The sensitivity, specificity and overall accuracy values for the FASTPlaqueTB assay relative to that of culture were respectively 76.5, 95 and 90 %. The corresponding values for the in-house IS6110-based PCR assay were 88, 91 and 90 % and, for Ziehl–Neelsen staining, were 59, 95 and 85 %. FASTPlaqueTB gave better clinical performance with urine samples than with sputum samples (sensitivity, specificity and overall accuracy were 100 % with urine samples and 64, 93 and 84 % with sputum samples). The 100 % sensitivity of FASTPlaqueTB was higher than that of the corresponding values for PCR (67 %) with urine samples. In conclusion, FASTPlaqueTB proved to be sensitive, cheap relative to the PCR and rapid. It is able to detect M. tuberculosis in clinical samples within 1 day, reducing the time to diagnosis in comparison with culture.
Gas-chromatographic lipid profiles in identification of currently known slowly growing environmental mycobacteria
Authors: Torkko Pirjo , Katila Marja-Leena , Kontro Merja
Published: April 2003

Cellular fatty acid analysis by GLC is widely used in the species identification of mycobacteria. Combining mycolic acid cleavage products with shorter cellular fatty acids increases the informative value of the analysis. A key has been created to aid in the identification of all currently known slowly growing environmental species. In this scheme, the species are classified into six categories, each characterized by a combination of fatty markers shared by those species. Within each category, individual species may be distinguished by the presence or absence of specific marker substances, such as methyl-branched fatty acids or secondary alcohols. This study also describes earlier unpublished GLC profiles of 14 rare, slowly growing, environmental mycobacteria,Mycobacterium asiaticum,Mycobacterium botniense,Mycobacterium branderi,Mycobacterium conspicuum,Mycobacterium cookii,Mycobacterium doricum,Mycobacterium heckeshornense,Mycobacterium heidelbergense,Mycobacterium hiberniae,Mycobacterium kubicae,Mycobacterium lentiflavum,Mycobacterium scrofulaceum,Mycobacterium triplexandMycobacterium tusciae. Though no single identification technique alone, even sequencing of an entire single gene such as 16S rRNA, can identify all mycobacterial species accurately, GLC has proven to be both reliable and reproducible in the identification of slowly growing mycobacteria. In cases of earlier unknown species, it generates useful information that allows their further classification and may lead to the description of novel species.
Time-Frequency Analysis of Nonlinear Systems: The Skeleton Linear Model and the Skeleton Curves
Authors: Wang Lili , Zhang Jinghui , Wang Chao , Hu Shiyue
Published: April 2003

The joint time-frequency analysis method is adopted to study the nonlinear behavior varying with the instantaneous response for a class of S.D.O.F nonlinear system. A time-frequency masking operator, together with the conception of effective time-frequency region of the asymptotic signal are defined here. Based on these mathematical foundations, a so-called skeleton linear model (SLM) is constructed which has similar nonlinear characteristics with the nonlinear system. Two skeleton curves are deduced which can indicate the stiffness and damping in the nonlinear system. The relationship between the SLM and the nonlinear system, both parameters and solutions, is clarified. Based on this work a new identification technique of nonlinear systems using the nonstationary vibration data will be proposed through time-frequency filtering technique and wavelet transform in the following paper.
Identification of Nonlinear Systems Through Time-frequency Filtering Technique
Authors: Wang Lili , Zhang Jinghui , Wang Chao , Hu Shiyue
Published: April 2003

In the previous paper, a class of nonlinear system is mapped to a so-called skeleton linear model (SLM) based on the joint time-frequency analysis method. Behavior of the nonlinear system may be indicated quantitatively by the variance of the coefficients of SLM versus its response. Using this model we propose an identification method for nonlinear systems based on nonstationary vibration data in this paper. The key technique in the identification procedure is a time-frequency filtering method by which solution of the SLM is extracted from the response data of the corresponding nonlinear system. Two time-frequency filtering methods are discussed here. One is based on the quadratic time-frequency distribution and its inverse transform, the other is based on the quadratic time-frequency distribution and the wavelet transform. Both numerical examples and an experimental application are given to illustrate the validity of the technique.
Investigation of Curved Polymeric Piezoelectric Active Diaphragms
Authors: Bailo Kelly C. , Brei Diann E. , Grosh Karl
Published: April 2003

Piezoelectric active diaphragms hold promise as an alternative to using passive diaphragms driven by voice coils for sound generation and noise cancellation applications. This paper presents an in-depth investigation of the acoustic response for curved polymeric piezoelectric active diaphragms. Simple analytical models were derived and experimentally validated to predict the structural dynamic and acoustic responses for generic polyvinylidene fluoride (PVdF) constant curvature active diaphragms with variable geometric parameters (width, radius, subtended angle, thickness). These models are useful for design purposes and for capturing the overall behavioral trends. To analyze the acoustic response mechanisms further, three-dimensional numerical models were also developed and experimentally validated. Parametric studies based upon these models reveal the potential of high acoustic outputs (over 100 dB in the far field) from optimized geometric configurations with subtended angles differing from the conventionally utilized flat, semicircular or circular configurations. These studies, corroborated by experiments on a variety of active diaphragm prototypes, conclude that the acoustic output is governed by the structural ring resonance, which can be designed such that the most efficient acoustic radiation is within the particular frequency range of operation.
Coupled Slow and Fast Dynamics of Flow Excited Elastic Cable Systems
Authors: Kim W.-J. , Perkins N. C.
Published: April 2003

Analytical studies of vortex-induced vibration (VIV) of cables during lock-in have considered small amplitude and relatively fast dynamic responses about an equilibrium configuration. However, this equilibrium may change as a result of the significantly increased mean drag created during lock-in. In response to increased drag, the cable may slowly drift downstream causing appreciable changes in cable geometry and tension. The resonance conditions for lock-in may be preserved during this slow drift or they may be disrupted. A nonlinear cable/fluid model is discussed that captures both fast (small amplitude) motions due to VIV and slow (large amplitude) motions due to drift.