bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric field and dielectrophoretic force on particles with a surface film
Authors: Techaumnat B. , Takuma T.
Published: November 2004

This article presents the analysis of the electric field and dielectrophoretic force on spherical particles with a surface film. In the analysis, we use the method of images with the fundamental solutions given for the various types of particles composed of a core and a surface film. The concept of the apparent conductivity is introduced to clarify the difference between the particle types. The analysis shows that the response of a particle with a surface film to an external field is unique and generally cannot be obtained by replacing the particle with a homogeneous particle. Using numerical examples, we compare the field and force characteristics between the particles that are of different types but exhibit an identical response to a uniform external field. The electric field and force are found smaller on the conductor-core particle but greater on the dielectric-core particle compared with the particle without any surface film. We have calculated the electric field and force by using the boundary element method in which a surface film is treated as a zero-thickness medium. The propriety of such treatment of a surface film depends not only on the film properties but also on the external field.
A method to characterize the interactions of external pulses and multiconductor lines in electromagnetic topology based simulations
Authors: Kirawanich Phumin , Kranthi Nakka , Gunda Rahul , Stillwell A. R. , Islam N. E.
Published: November 2004

Electromagnetic topology based simulations have been carried out to characterize the response of a semishielded multiconductor line to external electromagnetic pulses. The concept of transfer function generation through an aperture for this simulation technique is explained and a methodology to apply the concept to a multiconductor transmission line is proposed. Using this simulation approach the effects of conductor length, its distance from the aperture, and the response of the cable at various frequencies have been studied. The results compare well with experiments. The length of individual cables, its terminating impedances, and the distance of the individual cable from the aperture influences the behavior of the cables under external threat. Analysis shows that the effects from an external electromagnetic pulse are more severe than from lightning.
Rapid dissociation of merocyanine dye aggregates by reduced pressure in mixed Langmuir-Blodgett films
Authors: Hirano Yoshiaki , Murakami Takurou N. , Nakamura Yuhki K. , Fukushima Yoshinori , Tokuoka Yoshikazu , Kawashima Norimichi
Published: November 2004

We have examined the influence of reduced pressure on the redshifted and the blueshifted aggregates formed in the mixed Langmuir-Blodgett (LB) films of the merocyanine dye–arachidic acid (MS–C20) binary and the MS–C20–n-octadecane (MS-C20-AL18) ternary systems with the molar mixing ratios of [MS]:[C20]:[AL18]=1:2:x in the range of 0≦x≦5.0. The peak of the redshifted band at 590nm in the binary system remains constant before and after the reduced pressure treatments. On the other hand, not only the peaks of the blueshifted bands at 505nm and 520nm but also the redshifted shoulder at around 580nm in the ternary systems drastically diminishes after the treatments, indicating the dissociation of the MS aggregates. The long axis of AL18 molecules with the all-trans conformation, which tends to fill the MS empty spaces, is aligned along the stacking direction of the mixed LB films before the treatments, whereas almost all the AL18 molecules are absent after the treatments. Therefore, the dissociation is considered to be ascribed to the removal of the AL18 molecules with the uniaxial orientation in the mixed LB films by reduced pressure, leading to a change in the MS aggregation state.
Distinguishibility of oxygen desorption from the surface region with mobility dominant effects in nanocrystalline ceria films
Authors: Saraf Laxmikant , Shutthanandan V. , Zhang Y. , Thevuthasan S. , Wang C. M. , El-Azab Anter , Baer Donald R.
Published: November 2004

We present an investigation of oxygen (O18) uptake measurements in 1μm thick nanocrystalline ceria films grown on single crystal Al2O3(0001) by nuclear reaction analysis (NRA). Oxygen uptake measurements were carried out in the temperature range of 200–600°C at a background O18 pressure of 4.0×10−6Torr. Average grain size in the as-grown films, synthesized by sol-gel process was ∼3nm confirmed by high-resolution transmission electron microscopy and x-ray diffraction measurements. From the diffusion depth profiles, changes in intensity and slopes in surface and interface regions indicate complex oxygen mobility effects. Oxygen desorption is clearly distinguishable in the film surface region as a result of shift in the oxygen concentration maxima. It is argued that high defect density in nanocrystalline ceria which is associated with nanograin surface combined with intermediate temperature reducing environment triggers multiple processes such as molecular and ionic diffusion, adsorption, desorption, and isotope exchange interactions. The promising nature of NRA is realized as an effective tool to acquire the depth-dependent information from complex reactions existing in nanocrystalline environment.
Crystallization kinetics of Cu∕a-Si bilayer recording film under thermal and pulsed laser annealing
Authors: Her Yung-Chiun , Wu Chun-Lin
Published: November 2004

The crystallization kinetics of Cu∕a-Si bilayer recording film under thermal and pulsed laser annealing has been studied. Under thermal annealing, the crystallization temperature and activation energy for crystallization of a-Si with a thin Cu metal layer were reduced to about 485°C and 3.3±0.1eV, respectively. The reaction exponent was determined to be around 1.8, corresponding to a crystallization process in which grain growth occurs with nucleation, and the nucleation rate decreases with the progress of the grain growth process. Under pulsed laser annealing, the activation energy for crystallization of a-Si was estimated to be about 0.22eV which is significantly lower than that under thermal annealing and may be explained by the explosive crystallization of a-Si, while the reaction exponent was found to vary from 1.2 to 1.4, corresponding to a grain-growth-controlled process associated with instantaneous nucleation.
Light amplification in silicon nanocrystals by pump and probe transmission measurements
Authors: Dal Negro L. , Cazzanelli M. , Danese B. , Pavesi L. , Iacona F. , Franzò G. , Priolo F.
Published: November 2004

Net optical gain in silicon nanocrystals (Si-nc) has been measured by pump and probe transmission experiments. Si-nc active layers have been produced by plasma enhanced chemical vapor deposition on transparent quartz substrates. Continuous and pulsed pump and probe transmission measurements have shown clear evidences of net probe amplification with fast (nanosecond) response time. Transfer matrix and rate equations modeling of the nonlinear signal transmission allowed to extract the gain spectra for different pump intensities yielding good qualitative agreement with the experimental data. Gain cross sections per nanocrystals of the order of 3×10−16cm2 have been deduced. The physical origin of the optical amplification is interpreted within a four level recombination model describing the dynamics of strongly localized excitons at the Si-nc∕SiO2 interface.
Synthetic melanin thin films: Structural and electrical properties
Authors: da Silva M. I. N. , Dezidério S. N. , Gonzalez J. C. , Graeff C. F. O. , Cotta M. A.
Published: November 2004

Scanning probe microscopy was used to investigate the structural and electrical organization at the nanoscopic level of hydrated melanin thin films synthesized by oxidizing L-3-(3,4-dihydroxyphenyl)-alanine (L-dopa) in dimethyl sulfoxide. Atomic force microscopy (AFM) provided the morphologies of the L-dopa melanin films. Electrostatic force microscopy and conductive-AFM were used to spatially resolve the electrical properties of the material. Using a simple parallel plate capacitor model a method to measure the charge distribution on the sample was developed. The correlations between topography, electric charge, and current images of the sample demonstrated that the hydration process produces a restructuring of melanin observed not only through topographic variations, but also through the creation of areas with different electrical properties.
Synthesis of L1-(FeyPt100−y)100−xCux nanoparticles with high coercivity by annealing at 400°C
Authors: Kura Hiroaki , Sato Tetsuya
Published: November 2004

( Fe y Pt 100 − y ) 100 − x Cu x nanoparticles with various compositions were synthesized by the simultaneous polyol reduction of Pt(acac)2 and Cu(acac)2 and the thermal decomposition of Fe(CO)5. The as-made particles had a disordered fcc structure and an average diameter of ∼4.8nm. The result of x-ray diffraction indicated a transformation from fcc structure to fct structure in some samples after annealing at 400°C for 1h, and the c∕a ratio of lattice constant decreased with increasing Cu content. The doping of Cu clearly plays a significant role on the reduction of the ordering temperature in the ternary (FeyPt100−y)100−xCux alloy. In addition, the ordering of (FeyPt100−y)100−xCux nanoparticles is significantly dependent on the composition of Fe and Pt. As a result, (Fe47Pt53)74Cu26 nanoparticles have the coercive fields of ∼10 and ∼2kOe at 10K and room temperature, respectively.
Time evolution of plasma afterglow produced by femtosecond laser pulses
Authors: Martirosyan A. E. , Altucci C. , Bruno A. , de Lisio C. , Porzio A. , Solimeno S.
Published: November 2004

In this paper we investigate the time evolution of laser plasmas generated in atmospheric air by ultrashort (100fs) laser pulses. The detected quantity is the time integrated photon yield emitted by the plasma, which monotonically depends on the amount of energy transferred by the laser pulses to the plasma. We study the effect of a preionizing pulse on the efficiency of plasma generation by a second “probe” pulse and demonstrate that preionization results into a considerable increase of the overall photon yield emitted by the plasma. An explanation of this phenomenon relies on the fact that the larger the electron density experienced by the probe pulse, the more effective the energy transfer from the probe pulse to the residual plasma, the more intense is the light from the plasma. With this concept in mind and by relying on a pump-probe technique, we also measure the total photon yield emitted by the plasma produced by the combination of the two pulses, as a function of their relative delay time. We observe a considerable increase in the plasma brightness for delay times much longer than the laser pulse duration. This phenomenon is associated with an increase of the electron density even after the end of the pump pulse, due to secondary electron-impact ionization originating from highly-energetic primary photoelectrons, and to superelastic electron-molecule collisions. We also develop a simplified model describing the time evolution of the electron and ion densities and the electron temperature. From the calculated time evolution of these quantities produced by a single laser pulse, we can predict with a good approximation the main features of the plasma generated by an ultrashort laser pulse.
Plasma structure and behavior in a disk magnetohydrodynamic generator
Authors: Murakami Tomoyuki , Okuno Yoshihiro , Yamasaki Hiroyuki
Published: November 2004

We describe the structure and behavior of a nonequilibrium cesium-seeded helium plasma in a disk-shaped magnetohydrodynamic generator. Excellent time-resolved optical measurements clarify the spatial distribution of the electron temperature. A correlation analysis and the visualization of the plasma structure reveal its propagation phenomena from upstream to downstream and the transformation from a homogeneous quasisteady state to a self-consistent periodical state. A linear perturbation analysis suggests that the inhomogeneous plasma structure associated with the unique electron temperature behavior is closely related to ionization instability due to weak seed ionization.
Periodic reverse-twist nematic domains obtained by microrubbing patterns
Authors: Honma Michinori , Yamamoto Keisuke , Nose Toshiaki
Published: November 2004

A method for forming periodic 90° reverse-twist domains using a microscale rubbing pattern has been proposed; that is, an isolated 90° twist domain is surrounded by a 45° twist domain. Since liquid crystal (LC) materials exhibit elastic nature, the twist sense of the inner 90° twist domain prefers to be the same as that of the surrounding 45° twist domain. Two factors are investigated to obtain periodic 90° reverse-twist domains; (i) the injection process of LC material (isotropic or nematic phase) and (ii) the ratio of the area of the surrounding 45° twist domain and the whole area (the normalized area of the 45° twist domain). In the case of the injection in isotropic phase, it is revealed that periodic 90° reverse-twist domains can be obtained only when the area of the 45° twist domain is sufficiently large. On the other hand, in the case of injection in nematic phase, periodic 90° reverse-twist domains can successfully obtained regardless of the area of the 45° twist domain. Thus, the injection rocess is a very important factor to obtain periodic 90° reverse-twist domains. The fabricated LC cell with the periodic 90° reverse-twist domains is applied to LC grating. The almost linear relationship between the diffraction efficiency and the normalized area of the 45° twist domain is found and the high diffraction efficiency (0.39) near the theoretically maximum value (0.405) is obtained when the normalized area of the 45° twist domain is very small (0.1). The fabricated LC grating can function as a polarization-idependent and wavelength-independent LC grating.
Effects of postdeposition annealing on the dielectric properties of antiferroelectric lanthanum-doped lead zirconate stannate titanate thin films derived from pulsed laser deposition
Authors: Yao Yingbang , Lu S. G. , Chen Haydn , Wong K. H.
Published: November 2004

Lanthanum-doped lead zirconate stannate titanate antiferroelectric thin films were deposited onto Pt-buffered silicon substrates using the pulsed laser deposition method. The deposition temperature was 570°C. The postdeposition annealing process was carried out in an oxygen-flow tube furnace at temperatures ranging from 650 to 800°C for a duration of 30min; its effects were studied through the variations of the microstructure as well as the electrical and dielectric properties. It was found that an appropriate annealing process at temperatures above 700°Ccould substantially improve the dielectric properties. However, annealing beyond 800°C caused the film properties to deteriorate severely. Explanations were given with regard to the microstructure-property relationship.
High performance of cup-stacked-type carbon nanotubes as a Pt–Ru catalyst support for fuel cell applications
Authors: Kim Chan , Kim Yong Jung , Kim Yoong Am , Yanagisawa Takashi , Park Ki Chul , Endo Morinobu , Dresselhaus Mildred S.
Published: November 2004

The potential of cup-stacked-type carbon nanotubes (CSCNTs) as a catalyst support for the direct methanol fuel cells has been investigated by the electrochemical oxidation of methanol at various temperatures. The CSCNT-supported platinum–ruthenium (Pt–Ru) bimetallic catalyst exhibited twice as high a power density as the Pt–Ru catalyst supported on Vulcan XC-72 carbon, which is widely used as a catalyst support for the DMFC electrodes. The microscopic analysis of the CSCNT-supported Pt–Ru catalysts revealed that the bimetallic electrocatalysts were well dispersed on the CSCNT supports, and the particle size of the electrocatalysts was ca.5nm . The results of this work indicate that the performance of the carbon support materials is largely influenced by their electrical properties, morphology and crystallographic structures.
Study of the scattering of leaky Rayleigh waves at the extremity of a fluid-loaded thick plate
Authors: Declercq Nico F. , Teklu A. , Breazeale M. A. , Briers Rudy , Leroy Oswald , Degrieck Joris , Shkerdin Gennady N.
Published: November 2004

A study by means of the Schlieren technique for the visualization of the ultrasonic beams has revealed that when the leaky Rayleigh waves propagating along the horizontal edge of a thick fluid-loaded solid plate are scattered at the extremity of the plate, they travel around the corner and start leaking into the liquid along the Rayleigh angle measured from the normal to the vertical edge of the plate. Furthermore, the study reveals that the leaky Rayleigh waves are stimulated by the border of an incident ultrasonic-bounded beam more than by the interior of the beam. A comparison with an earlier work shows that the characteristics of the scattering of the leaky Rayleigh waves at the edge of the plate is very different from that of the Scholte–Stoneley waves.
High-quality boron-doped homoepitaxial diamond grown by high-power microwave-plasma chemical-vapor deposition
Authors: Teraji Tokuyuki , Arima Kazuya , Wada Hideki , Ito Toshimichi
Published: November 2004

Boron-doped homoepitaxial diamond (100) films with substantially flat surface have been deposited by a high-power microwave-plasma chemical-vapor-deposition (MPCVD) method. Hall mobilities of 1500cm2∕Vs at 290K and 2220cm2∕Vs at 235K were attained for such a specimen with an acceptor density of 1.4×1018cm−3 grown at a growth rate of 3.5μm∕h. These mobilities are comparable with those of the highest quality homoepitaxial diamond grown by a standard low-power MPCVD method, where the growth rate and carrier concentration were, respectively, ∼1∕30 and 1∕5 of the corresponding values attained in the present case. This fact verifies that the high-power MPCVD is suitable for deposition of a high quality and high carrier-concentration p-type diamond at a reasonably high growth rate.
Polarization-independent electrically tunable phase grating fabricated from ultraviolet-curable liquid crystals
Authors: Ghosh Anup K. , Choi Suk-Won , Takanishi Yoichi , Park Byoungchoo , Ishikawa Ken , Ono Yoshiyuki , Kawamura Joji , Takezoe Hideo
Published: November 2004

Polarization-independent electrically tunable Raman-Nath phase diffraction grating has been fabricated using a very simple technique involving photocurable liquid crystals. The structure consists of alternating stripe of twisted-nematic liquid crystal domains and polymerized homeotropic ones. The diffraction efficiency can be tuned by an applied electric field, and is independent of the incident polarization particularly slightly above an electric field to make a Frederiks transition.
Internal friction study on CuFe2O4∕PbZr0.53Ti0.47O3 composites
Authors: Dai Y. R. , Bao P. , Zhu J. S. , Wan J. G. , Shen H. M. , Liu J. M.
Published: November 2004

The xCuFe2O4(CFO)-(1−x)PbZr0.53Ti0.47O3(PZT) composites with x=0.1, 0.2, and 0.3 have been prepared by solid state reaction method. Two separate CFO and PZT phases without mixture phase have been confirmed by X-ray diffraction. The internal friction spectra at various frequencies were measured from 90 to 700K. The internal friction peaks observed in those samples can be assigned to the contributions of ferroelectric and copper ferrite, respectively. There is no coupling of mechanical dissipation between the two components. The magnetoelectric (ME) property of the composites were also determined and the dependence of ME coefficient on CFO concentration were discussed.
Interdiffusion and structural change in an InGaAs dots-in-a-well structure by rapid thermal annealing
Authors: Park Young Min , Park Young Ju , Kim Kwang Moo , Song Jin Dong , Lee Jung II , Yoo Keon-Ho , Kim Hyung Seok , Park Chan Gyung
Published: November 2004

Post-growth rapid thermal annealing (RTA) has been used to investigate an interdiffusion and the structural change in an InGaAs dots-in-a-well (DWELL) structure grown by molecular beam epitaxy using an alternately supplying InAs and GaAs sources. In the case of the as-grown sample, which has a metastable quantum structure due to an intentional deficit of source materials, it is found that an InGaAs quantum well (QW) coexists with the premature quantum dots (QDs), and an intermediate layer exists between the QW and the QDs. Through the RTA process at 600 and 800°C for 30s, metastable structure changes into a normal DWELL structure composed of QDs and QW as a result of the intermixing of premature QDs and the intermediate layer.
The equation of state of a fluorinated tripolymer
Authors: Millett J. C. F. , Bourne N. K. , Gray G. T.
Published: November 2004

The Hugoniot of the fluorinated tripolymer Viton B has been quantified in terms of shock stress, shock velocity, and particle velocity. The shock velocity—particle velocity curve was found to be linear, thus suggesting no changes in phase occurred in the experimental stress range investigated. Comparisons of the calculated hydrodynamic pressures and measured stresses also showed close agreement, with only small differences apparent at the highest stresses. It is believed that this shows Viton B has a low shock-induced shear strength that only becomes significant at high impact stresses. Comparison of the Hugoniots of Viton B, polytetrafluroethylene, and polyvinylidene difluoride shows that the former is slightly steeper. The authors suggest that this is due to the −CF3 side group having a strengthening effect.
La
0.8
Sr
0.2
MnO
3
-heterostructure effects on the dielectric properties of PbTiO3-based thin films
Authors: Es-Souni M. , Girdauskaite E. , Iakovlev S. , Solterbeck C.-H. , Zaporojtchenko V.
Published: November 2004

The present paper deals with substrate heterostructure effects on the microstructure and dielectric properties of Sm, Er, and La doped lead titanate (PT) thin films. The substrate heterostructures chosen include Si∕(La0.8Sr0.2)MnO3 (LSMO), Y-stabilized zirconia (YSZ)∕LSMO and Si∕Pt. Both LSMO and PT thin films were processed via chemical solution deposition. The results are compared to those of Sm and Er doped lead-zirconate-titanate (PZT). It is shown that the dielectric properties, and particularly the ferroelectric-to-paraelectric transition temperature of PT, are strongly affected by the substrate heterostructure. In comparison to PT on platinized Si, the transition temperature is shifted by more than 100°C towards lower values in the case of Er and Sm doped PT on LSMO, while those of La doped PT and PZT are not affected at all. X-ray photoelectron spectroscopy investigations show a substantial interdiffusion between LSMO and PT. Particularly the diffusion of La towards the ferroelectric film and that of Pb towards LSMO are made responsible for the change in the dielectric properties. In the case of PZT we stipulate the formation of a stable pyrochlore diffusion barrier layer.
Magnetoresistance characterization of nanometer Si metal-oxide-semiconductor transistors
Authors: Meziani Y. M. , Łusakowski J. , Knap W. , Dyakonova N. , Teppe F. , Romanjek K. , Ferrier M. , Clerc R. , Ghibaudo G. , Boeuf F. , Skotnicki T.
Published: November 2004

We report on the high-field (up to 10T) magnetoresistance measurements performed on the short (down to 75-nm gate length) n-type Si metal-oxide-semiconductor field-effect transistors. The electron magnetoresistance mobility of these nanometer devices was determined for a wide range of the electron concentration (107–1013cm−2, i.e., from a weak to a strong inversion) and gate length (10μm–75nm). In the case of long samples, the magnetoresistance mobility was compared to the effective mobility obtained by the standard parameter extraction and the split C–V techniques. The results are discussed in terms of the scattering power-law two-dimensional transport analysis. The data clearly indicate a significant decrease of the mobility with the gate length reduction below 100nm.
Relaxor properties of lanthanum-doped bismuth layer-structured ferroelectrics
Authors: Chen Xiao-Bing , Hui Rong , Zhu Jun , Lu Wang-Ping , Mao Xiang-Yu
Published: November 2004

Several polycrystalline samples of bismuth layer-structured ferroelectrics (BLSF) family doped by lanthanum, Bi4−xLaxTi3O12, SrBi4−xLaxTi4O15, Sr2Bi4−xLaxTi5O18, and (Bi,La)4Ti3O12-Sr(Bi,La)4Ti4O15, were prepared by the traditional solid-state reaction method. Their ferroelectric and dielectric properties were investigated. The dielectric measurement data showed that the content of lanthanum determined the ferroelectric characteristics of the compounds. In each series samples, they behaved as normal ferroelectrics for small x, but all of them tended to become relaxors when x was increased. The critical value of the La content causing relaxor characteristics is different for the different BLSFs due to the difference of the number of strontium atoms in their crystal structures. The appearance of the relaxor behavior was attributed to a ferroelectric microdomain state induced by random fields.
Laser self-induced thermo-optical effects in a magnetic fluid
Authors: Pu Shengli , Chen Xianfeng , Liao Weijun , Chen Lijun , Chen Yuping , Xia Yuxing
Published: November 2004

The laser self-induced thermo-optical effects in a magnetic fluid are studied in this work. We study the origin of these effects theoretically, and then experiments are done to investigate the relationship between the divergence angle of the laser beam and the incident power. From the experimental results, we find out that the divergence angle increases linearly with the incident power to some critical power, which is in good agreement with the theory. To the high incident power side, the divergence angle will deviate from the linear relationship and the spherical aberration interference rings will be blurred due to the occurrence of the convective currents.
Nanopatterning of epitaxial CoSi2 using oxidation in a local stress field and fabrication of nanometer metal-oxide-semiconductor field-effect transistors
Authors: Zhao Q. T. , Kluth P. , Bay H. L. , Lenk St. , Mantl S.
Published: November 2004

A patterning method for the generation of epitaxial CoSi2 nanostructures was developed based on anisotropic diffusion of Co∕Si atoms in a stress field during rapid thermal oxidation (RTO). The stress field is generated along the edge of a mask consisting of a thin SiO2 layer and a Si3N4 layer. During RTO of the masked silicide structure, a well-defined separation of the silicide layer forms along the edge of the mask. The technique was used to make 50-nm channel-length metal-oxide-semiconductor field-effect transistors (MOSFETs). These highly uniform gaps define the channel region of the fabricated device. Two types of MOSFETs have been fabricated: symmetric transistor structures, using the separated silicide layers as Schottky source and drain, and asymmetric transistors, with n+ source and Schottky drain. The asymmetric transistors were fabricated by an ion implantation into the unprotected CoSi2 layer and a subsequent out diffusion to form the n+ source. The detailed fabrication process as well as the I–V characteristics of both the symmetric and asymmetric transistor structures will be presented.
Hydrophobic interactions drive ligand-receptor recognition for activation and inhibition of staphylococcal quorum sensing
Authors: Wright Jesse S. , Lyon Gholson J. , George Elizabeth A. , Muir Tom W. , Novick Richard P.
Published: November 2004

Two-component systems represent the most widely used signaling paradigm in living organisms. Encoding the prototypical two-component system in Gram-positive bacteria, the staphylococcal
agr
(accessory gene regulator) operon uses a polytopic receptor, AgrC, activated by an autoinducing peptide (AIP), to coordinate quorum sensing with the global synthesis of virulence factors. The
agr
locus has undergone evolutionary divergence, resulting in the formation of several distinct inter- and intraspecies specificity groups, such that most cross-group AIP-receptor interactions are mutually inhibitory. We have exploited this natural diversity by constructing and analyzing AgrC chimeras generated by exchange of intradomain segments between receptors of different
agr
groups. Functional chimeras fell into three general classes: receptors with broadened specificity, receptors with tightened specificity, and receptors that lack activation specificity. Testing of these chimeric receptors against a battery of AIP analogs localized the primary ligand recognition site to the receptor distal subdomain and revealed that the AIPs bind primarily to a putative hydrophobic pocket in the receptor. This binding is mediated by a highly conserved hydrophobic patch on the AIPs and is an absolute requirement for interactions in self-activation and cross-inhibition of the receptors. It is suggested that this recognition scheme provides the fundamental basis for
agr
activation and interference.
Molecular dynamics simulations of spontaneous fibril formation by random-coil peptides
Authors: Nguyen Hung D. , Hall Carol K.
Published: November 2004

Assembly of normally soluble proteins into amyloid fibrils is a cause or associated symptom of numerous human disorders, including Alzheimer's and the prion diseases. We report molecular-level simulation of spontaneous fibril formation. Systems containing 12-96 model polyalanine peptides form fibrils at temperatures greater than a critical temperature that decreases with peptide concentration and exceeds the peptide's folding temperature, consistent with experimental findings. Formation of small amorphous aggregates precedes ordered nucleus formation and subsequent rapid fibril growth through addition of β-sheets laterally and monomeric peptides at fibril ends. The fibril's structure is similar to that observed experimentally.
A Novel Thermodynamic Relationship Based on Kramers Theory for Studying Enzyme Kinetics under High Viscosity
Authors: Siddiqui Khawar Sohail , Bokhari Saleem Ahmed , Afzal Ahmed Jawaad , Singh Surjit
Published: November 2004

In most studies of enzyme kinetics it has been found sufficient to use the classical Transition State Theory (TST) of Eyring and others. This theory was based on the solvent being an ideal dilute substance treated as a heat bath. However, enzymes found in organisms adapted to very low (psychrophiles) and very high (thermophiles) temperatures are also subjected to variable solute concentrations and viscosities. Therefore, the TST may not always be applicable to enzyme reactions carried out in various solvents with viscosities ranging from moderate to very high. There have been numerous advances in the theory of chemical reactions in realistic non‐ideal solvents such as Kramers Theory. In this paper we wish to propose a modified thermodynamic equation, which have contributions from kcat, Km and the viscosity of the medium in which the enzyme reaction is occurring. These could be very useful for determining the thermodynamics of enzymes catalyzing reactions at temperature extremes in the presence of substrate solutions of different compositions and viscosities. IUBMB Life, 56: 403‐407, 2004
Gene Expression Profiling of p53+/‐ Knockout and Wild‐type Mice Following Diethylstilbestrol Administration
Authors: Salleh Mohd Nazil , Ismail Patimah , Abdullah Abdul Salam , Taufiq‐Yap Yun Hin , Carmichael Paul
Published: November 2004

Studies with clastogenic carcinogen diethylstilbestrol (DES) resulted in a broad of spectrum of toxic and carcinogenic effects in humans and rodents, but the cellular and molecular mechanism(s) by which it induces cancer is not clear. To identify putative genetic targets for p53 in vivo, we applied the cDNA macroarray gene expression profiles associated with apoptosis by comparing p53+/‐ knockout mice and wild‐type mice on the kidney and uterus of female mice. p53+/‐ knockout mice and wild‐type mice were treated with DES (500 μmole kg‐1) or vehicle i.p once daily for 4 days. Total RNAs were obtained from kidney and uterus of both control and DES‐treated. The signal intensities of individual gene spots on the membrane were quantified and normalized to the expression level of the GAPDH gene as an internal control. Our results demonstrated that 16 genes; bad, bax, bcl‐2, bcl‐w, bcl‐x, caspase‐3, caspase‐7, caspase‐8, c‐myc, E124, GADD45, mdm2, NKκb1, p53, p21, Rb and trail were up‐regulated and six genes; caspase‐1, caspase‐2, DR5, E2F1, FasL and iNOS did not changed in response to DES treatment in wild‐type mice compared to p53+/‐ knockout mice. Most genes are involved in cell cycle regulation, signal transduction, apoptosis, or transcription. The greatest changes were seen in bad, bcl‐x, mdm2, p53 and p21 gene expression in wild‐type mice compared to p53+/‐ knockout mice. In comparing p53 and p21 gene expression in wild‐type mice and p53+/‐ knockout mice, there was an 4.4‐fold vs. 1.8‐fold; 8‐fold vs. 5.2‐fold for kidney and16‐fold vs. 5.5‐fold; 2.1‐fold vs. 8.3‐fold for uterus samples increase in induction (respectively). RT‐PCR and densitometric analysis was used to confirm the biggest changes of p21, p53 and bax genes. Using this approach, we have identified apoptosis associated genes regulated in response to DES and have revealed putative differences between the isogenic parent strain and p53+/‐ knockout mice, which will contribute to a better understanding of toxicity/carcinogenicity mechanisms in this model. IUBMB Life, 56: 409‐416, 2004
Protecting Pancreatic ß‐cells
Authors: Pileggi Antonello , Fenjves Elizabeth , Klein Dagmar , Ricordi Camillo , Pastori Ricardo
Published: November 2004

Type 1 diabetes mellitus is an autoimmune disorder in which the insulin‐producing β‐cells of the pancreatic islets of Langerhans are selectively destroyed. Transplantation of allogeneic islets offers a novel therapeutic approach for type 1 diabetic patients. Primary obstacles to the successful outcome of this treatment are loss of the islets occurring first during the isolation procedure and then immediately following transplantation. The genetic make up of β‐cells contributes to making them particularly vulnerable to apoptosis and necrosis‐induced cell death caused by the trauma of the isolation procedure and by non‐specific inflammatory events at the transplantation site. In this review we present description of chemical and molecular biology based strategies to confer cytoprotection to β‐cells. IUBMB Life, 56: 387‐394, 2004
Methanococcus vannielii Selenium Metabolism: Purification and N‐terminal Amino Acid Sequences of a Novel Selenium‐binding Protein and Selenocysteine Lyase
Authors: Stadtman Thressa
Published: November 2004

Selenium is an essential component of several enzymes and proteins in a number of methane‐producing archae. Information concerning accessory proteins that function in selenium transport processes, however, is limited. A novel selenium‐binding protein with a potential transport role and a selenocysteine lyase that serves as a selenium delivery protein are present in Methanococcus vannielii. The selenium‐binding protein was purified from extracts of 75Se‐labeled cells. Although there was gradual loss of 75Se during purification, the isolated protein still could be detected as a radioactive 42 kDa species on native PAGE gels and as a 33 kDa species on SDS PAGE gels. The N‐terminal amino acid sequence of residues 1 ‐ 63 of the protein was determined by automated Edman degradative analysis. The only homologous sequence detected in the recorded data base was that of a gene encoding an unknown protein located in the genomic sequence of Methanococcus maripaludis. Cloning and expression of the corresponding gene from M. vannielii are described in a manuscript in press (Self et al.). A 47 kDa selenocysteine lyase isolated from M. vannielii extracts exhibited sequence homology to the NIFS family of proteins that transport sulfur. The purified selenocysteine lyase catalyzed the elimination of an elemental form of selenium from free selenocysteine and delivered this selenium directly to selenophosphate synthetase. The synthetase converted the selenium to selenophosphate in an ATP‐dependent reaction. IUBMB Life, 56: 427‐431, 2004
Androgen Receptor Gene Methylation and Exon One CAG Repeat Length in Ovarian Cancer: Differences from Breast Cancer
Authors: Kassim Samar , Zoheiry Nivan , Hamed Wael , Going James , Craft John
Published: November 2004

More than one neoplastic founder clone can exist in benign epithelial tumours. Although theories of clonal selection make pluriclonality appear unlikely in carcinomas, published data do not exclude this possibility. This study looked for evidence of multiclonal X inactivation in ovarian carcinoma using AR methylation as a marker. Fifteen unifocal ovarian carcinomas and 14 multifocal carcinomas all in Scottish patients were studied. One representative formalin‐fixed paraffin‐embedded tumour block was chosen for each of the former and two for the latter. From each of these 43 tumour blocks three samples each of ∼104 carcinoma cells were obtained by microdissection (129 in all). DNA released by proteinase K digestion was subjected to PCR amplification of the androgen receptor gene AR exon I CAG repeat polymorphism with and without prior digestion with methylation‐sensitive restriction enzymes HpaII and HhaI. Complex amplification patterns were consistent with mosaic X inactivation in some ovarian carcinomas but acquired anomalies of AR methylation cannot be excluded. Parallel analysis of other X‐linked polymorphic loci would strengthen the inference of clonality status from DNA methylation data in tumour X studies. Strikingly, the number of CAG repeats in the 29 ovarian tumour patients (median 16, range 11 ‐ 20) was substantially fewer than in 34 previously studied breast cancer patients from the same scottish population (median 21, range 14 ‐ 26; P < 0.0001), and women homozygous for the AR CAG repeat were over‐represented in the ovarian cancer patients but not in the breast cancer series. These findings reinforce recent suggestions that AR may have a role in ovarian carcinogenesis. IUBMB Life, 56: 417‐426, 2004
A Survey of Current Rehabilitation Trends for Burn Injuries to the Head and Neck
Authors: Serghiou Michael A. , Holmes Christina L. , McCauley Robert L.
Published: November 2004

Burn injuries to the face and neck present a unique challenge to the burn team and must be treated with considerable care and vigilance by the rehabilitation team to prevent potential contractures that may occur. Standard guidelines for treatment of the head and neck have not been established. This article presents the results of a comprehensive survey that examined the similarities and differences in the rehabilitation techniques used in various burn centers for the treatment of these injuries. The results obtained from the survey responses demonstrate several similarities in treatment throughout the continuum of care, revealing the potential for the development of a uniform rehabilitation protocol for the treatment of burn injuries to the face and neck.
The Medical Use of a Nonmedical Product: Melted Tar
Authors: Terzioglu Ahmet , Sarifakioglu Nedim , Yavuz Nurten , Aslan Gürcan
Published: November 2004

The use of hot tar in industry is widespread, and burns caused by this agent remain a problem. Instead of being classified as chemical injuries, these burns compose a unique class of thermal injury because of the difference of mechanisms of injury and the difficulties in removing the agent from the skin. Tar burns usually are occupational in nature and are observed mostly in male patients. This report presents a female burn case that had occurred after she applied hot tar to her skin for the treatment purposes of pain relief.
Sandal Burns and Their Treatment in Children
Authors: Shakirov Babur M.
Published: November 2004

Sandal is an ancient, primitive heating device that is still in use by both poor and rich people in mountain areas of Middle Asia. Sandal burn injuries are a serious health problem. Characteristics of sandal burns include not only skin injuries of various depths but also injuries to underlying tissues: subcutaneous fat, fasciae, muscles, and even bones. Sandal burns are characterized by such severe deep injuries because of a close contact of the body with live coals or woods. The main goal of this work was to present the most complete information about sandal burns and discuss the most effective methods of treatment for sandal burns. This treatment is used to accelerate the rejection of necrotic tissue, to prepare the wound for early autodermoplastic surgery, to decrease the postburn contractures/deformities, and also to shorten hospital stay for the patients.
Are We Headed for a Shortage of Burn Surgeons?
Authors: Faucher Lee D.
Published: November 2004

Newly trained burn surgeons are in high demand but low supply. The purpose of this study was to quantitate the current need for burn surgeons and to identify the need in the future. A questionnaire was sent to the 159 burn care facilities in North America listed in the 1999 to 2000 American Burn Association Directory. Of the 159 centers, 9 surveys were returned stating the center did not exist. Eighty-four (56%) of the remaining 150 centers responded. Twenty-nine percent of responding burn centers are currently attempting to recruit another burn surgeon, and an additional 38% anticipate needing to recruit one within the next 5 years. Of these, 89% anticipate difficulty finding another burn surgeon. This survey identifies a need for burn surgeons now and warns of a severe shortage in the immediate future. Current burn surgeons need to ensure that any interested trainee be mentored appropriately toward a career in burn surgery.
The Serratia gene cluster encoding biosynthesis of the red antibiotic, prodigiosin, shows species- and strain-dependent genome context variation
Authors: Harris Abigail K. P. , Williamson Neil R. , Slater Holly , Cox Anthony , Abbasi Sophia , Foulds Ian , Simonsen Henrik T. , Leeper Finian J. , Salmond George P. C.
Published: November 2004

The prodigiosin biosynthesis gene cluster (pigcluster) from two strains ofSerratia(S. marcescensATCC 274 andSerratiasp. ATCC 39006) has been cloned, sequenced and expressed in heterologous hosts. Sequence analysis of the respectivepigclusters revealed 14 ORFs inS. marcescensATCC 274 and 15 ORFs inSerratiasp. ATCC 39006. In eachSerratiaspecies, predicted gene products showed similarity to polyketide synthases (PKSs), non-ribosomal peptide synthases (NRPSs) and the Red proteins ofStreptomyces coelicolorA3(2). Comparisons between the twoSerratia pigclusters and theredcluster fromStr. coelicolorA3(2) revealed some important differences. A modified scheme for the biosynthesis of prodigiosin, based on the pathway recently suggested for the synthesis of undecylprodigiosin, is proposed. The distribution of thepigcluster within severalSerratiasp. isolates is demonstrated and the presence of cryptic clusters in some strains shown. Thepigcluster ofSerratia marcescensATCC 274 is flanked bycueRandcopAhomologues and this configuration is demonstrated in severalS. marcescensstrains, whilst these genes are contiguous in strains lacking thepigcluster.
σ B-dependent gene induction and expression in Listeria monocytogenes during osmotic and acid stress conditions simulating the intestinal environment
Authors: Sue David , Fink Daniel , Wiedmann Martin , Boor Kathryn J.
Published: November 2004

Listeria monocytogenesmust overcome a variety of stress conditions in the host digestive tract to cause foodborne infections. The alternative sigma factorσB, encoded bysigB, is responsible for regulating transcription of severalL. monocytogenesvirulence and stress-response genes, including genes that contribute to establishment of gastrointestinal infections. A quantitative RT-PCR assay was used to measure mRNA transcript accumulation for the virulence genesinlAandbsh, the stress-response genesopuCAandlmo0669(encoding a carnitine transporter and an oxidoreductase, respectively) and the housekeeping generpoB. Assays were conducted on mid-exponential phaseL. monocytogenescells exposed to conditions reflecting osmotic (0·3 M NaCl) or acid (pH 4·5) conditions typical for the human intestinal lumen. In exponential-phase cells, as well as under osmotic and acid stress,inlA,opuCAandbshshowed significantly lower absolute expression levels in aL. monocytogenesΔsigBnull mutant compared to wild-type. A statistical model that normalized target gene expression relative torpoBshowed that accumulation ofinlA,opuCAandbshtranscripts was significantly increased in the wild-type strain within 5 min of acid and osmotic stress exposure;lmo0669transcript accumulation increased significantly only after acid exposure. It was concluded thatσBis essential for rapid induction of the tested stress-response and virulence genes under conditions typically encountered during gastrointestinal passage. AsinlA,bshandopuCAare critical for gastrointestinal infections in animal models, the data also suggest thatσBcontributes to the ability ofL. monocytogenesto cause foodborne infections.
The Pseudomonas aeruginosa global regulator MvaT specifically binds to the ptxS upstream region and enhances ptxS expression
Authors: Westfall Landon W. , Luna A. Marie , Francisco Michael San , Diggle Stephen P. , Worrall Kathryn E. , Williams Paul , Cámara Miguel , Hamood Abdul N.
Published: November 2004

Exotoxin A production inPseudomonas aeruginosais regulated positively or negatively by several genes. Two such regulatory genes,ptxRandptxS, which are divergently transcribed from each other, have been described previously. While computer analysis suggested that theptxR-ptxSintergenic region contains potential binding sites for several regulatory proteins, the mechanism that regulates the expression of eitherptxRorptxSinP. aeruginosais not known. The presence of aP. aeruginosaprotein complex that specifically binds to a segment within this region was determined. In this study the binding region was localized to a 150 bp fragment of the intergenic region and the proteins that constitute the binding complex were characterized asP. aeruginosaHU and MvaT. Recombinant MvaT was purified as a fusion protein (MAL-MvaT) and shown to specifically bind to theptxR-ptxSintergenic region. A PAO1 isogenic mutant defective inmvaT, PAOΔmvaT, was constructed and characterized. The lysate of PAOΔmvaTfailed to bind to the 150 bp probe. The effect ofmvaTonptxSandptxRexpression was examined using real-time PCR experiments. The expression ofptxSwas lower in PAOΔmvaTthan in PAO1, but no difference was detected inptxRexpression. These results suggest that MvaT positively regulatesptxSexpression by binding specifically to theptxSupstream region.
Identification and occurrence of tetrad-forming Alphaproteobacteria in anaerobic–aerobic activated sludge processes
Authors: Wong Man-Tak , Tan Fea Mein , Ng Wun Jern , Liu Wen-Tso
Published: November 2004

In an acetate-fed anaerobic–aerobic membrane bioreactor, a deteriorated enhanced biological phosphorus removal (EBPR) community was developed (as determined based on the chemical profiles of organic substrate, soluble phosphate, and intracellular carbohydrate and polyhydroxyalkanote (PHA) concentrations). Microscopic observations revealed the dominance of tetrad-forming organisms (TFOs), of which the majority stained positively for PHA under anaerobic conditions. Fluorescencein situhybridization (FISH) confirmed that theAlphaproteobacteria(85·0±7·0 % of total cells) were the most dominant group. A 16S rRNA gene clone library specific for theAlphaproteobacteriaindicated that most 16S rRNA gene clones (61 % of total clones) were closely affiliated with ‘Defluvicoccus vanus’, forming a cluster within subgroup 1 of theAlphaproteobacteria. Combined PHA staining and FISH with specific probes designed for the members of the ‘Defluvicoccus’ cluster suggested diversity within this TFO cluster, and that these TFOs were newly identified glycogen-accumulating organisms in EBPR systems. However, these ‘Defluvicoccus’-related TFOs were only seen in low abundance in 12 different EBPR and non-EBPR systems, suggesting that they were not the key populations responsible for the deterioration of full-scale EBPR processes.