bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser surface wakefield in a plasma column
Authors: Gorbunov L. M. , Mora P. , Ramazashvili R. R.
Published: October 2003

The structure of the wakefield in a plasma column, produced by a short intense laser pulse, propagating through a gas affected by tunneling ionization is investigated. It is shown that besides the usual plasma waves in the bulk part of the plasma column [see Andreev et al., Phys. Plasmas 9, 3999 (2002)], the laser pulse also generates electromagnetic surface waves propagating along the column boundary. The length of the surface wake wave substantially exceeds the length of the plasma wake wave and its electromagnetic field extends far outside the plasma column.
Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln=La, Pr, and Nd; Ch=S or Se) semiconductor alloys
Authors: Hiramatsu Hidenori , Ueda Kazushige , Takafuji Kouhei , Ohta Hiromichi , Hirano Masahiro , Kamiya Toshio , Hosono Hideo
Published: October 2003

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln=La, Pr, and Nd; Ch=S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ∼30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ∼80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2− layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices.
Dielectric selective mirror for intracavity wavelength selection in far-infrared p-Ge lasers
Authors: Du Bosq T. W. , Peale R. E. , Nelson E. W. , Muravjov A. V. , Fredricksen C. J. , Tache N. , Tanner D. B.
Published: October 2003

A robust metal-free intracavity fixed-wavelength selector for the cryogenically cooled far-infrared p-Ge laser is demonstrated. The device is a back mirror consisting of a thin silicon etalon and dielectric SrTiO3 flat. A laser line width of 0.2 cm−1 is achieved, which corresponds to an active cavity finesse of ∼0.15. The wavelength position and spectral purity are maintained over a wide range of laser operating fields. Use of SrTiO3 lowers the laser resonance line frequencies by ∼1 cm−1 compared with expectations for metal mirrors. The effect is due to phase shift, which is determined from far-infrared reflectivity measurements of SrTiO3. A p-Ge laser with such selector is free from danger of electrical breakdown and mirror oxidation during repeatable thermal cycling, which makes it more reliable than previous selection schemes for practical applications.
On effective constraints for the Riemann–Lanczos system of equations
Authors: Edgar S. Brian
Published: October 2003

There have been conflicting points of view concerning the Riemann–Lanczos problem in three and four dimensions. Using direct differentiation on the defining partial differential equations, Massa and Pagani (in four dimensions) and Edgar (in dimensions n⩾3) have argued that there are effective constraints so that not all Riemann tensors can have Lanczos potentials; using Cartan’s criteria of integrability of ideals of differential forms Bampi and Caviglia have argued that there are no such constraints in dimensions n⩽4, and that, in these dimensions, all Riemann tensors can have Lanczos potentials. In this article we give a simple direct derivation of a constraint equation, confirm explicitly that known exact solutions of the Riemann–Lanczos problem satisfy it, and argue that the Bampi and Caviglia conclusion must therefore be flawed. In support of this, we refer to the recent work of Dolan and Gerber on the three-dimensional problem; by a method closely related to that of Bampi and Caviglia, they have found an “internal identity” which we demonstrate is precisely the three-dimensional version of the effective constraint originally found by Massa and Pagani, and Edgar.
Kr–Cl stretching vibration of HKrCl: Matrix-isolation and anharmonic ab initio study
Authors: Lignell A. , Lundell J. , Pettersson M. , Khriachtchev L. , Räsänen M.
Published: October 2003

The Kr–Cl stretching vibration of HKrCl molecule is studied. The absorption shows Cl35 and Cl37 isotopic splitting due to natural abundance of the Cl isotopes. The observed Kr–Cl stretching vibrations of the HKrCl are at 253.1 (35Cl) and 248.3 cm−1 (37Cl). Experimentally, deuteration of the HKrCl does not cause a shift of the Kr–Cl stretching frequency. In addition to the Kr–Cl stretching mode, the bending mode of DKrCl is observed at 397.7 cm−1. The vibrational analysis suggests that the Kr–Cl bond shows some covalent character in addition to the ionic. Anharmonic ab initio calculations are employed to verify the vibrational properties of various isotopologues of HKrCl.
Monte Carlo simulations of krypton adsorption in nanopores: Influence of pore-wall heterogeneity on the adsorption mechanism
Authors: Kuchta B. , Llewellyn P. , Denoyel R. , Firlej L.
Published: October 2003

We present molecular simulation results of the adsorption of krypton in a model of the mesoporous material MCM-41. The adsorption isotherm and adsorption enthalpies are studied at 77 K. Comparison of the experimental and simulation data allows us to analyze how the available interaction models (Kr–Kr and Kr–walls) are able to reproduce the experimental situation. The role of the heterogeneous interactions versus the homogenous model is studied and compared with the previous simulation results of nitrogen adsorption in MCM-41. The results show that a model of ideal cylindrical pores gives qualitatively and quantitatively different results. A distribution of the adsorption sites must exist to explain the loading at low pressure (below capillary condensation). Such a distribution in MCM-41 is a consequence of inhomogenous walls that contain a wide variety of attractive sites ranging from weakly attractive silica-type to highly attractive regions. In our simulations the MCM-41 structure is modeled as an amorphous array of oxygen and silicon atoms, each one interacting with an adsorptive atom via the atom–atom potential. The distribution of the adsorption sites is merely a consequence of the local atomic structure. Such a model of the wall reproduces the smooth increase in loading seen experimentally.
Effects of dust-charge fluctuations on the potential of an array of projectiles in a partially ionized dusty plasma
Authors: Ali S. , Nasim M. H. , Murtaza G.
Published: October 2003

The expressions for the Debye and the wake potential are derived by incorporating dust-charge fluctuations of a single projectile, as well as of an array of dust grain projectiles, propagating through a partially ionized dusty plasma with a constant velocity. Numerically, the effects of the dust-charge fluctuations and the dust–neutral collisions on the electrostatic potential for a single, three, six and ten projectiles are examined. The dust-charge relaxation rate modifies the shape of the Debye as well as the wake potential. For smaller values of the relaxation rates a potential well is formed instead of Debye potential.
Analytic model for a dual frequency capacitive discharge
Authors: Kim H. C. , Lee J. K. , Shon J. W.
Published: October 2003

A homogeneous plasma model for dual radio-frequency (rf) discharges driven by two sinusoidal current sources has been analyzed. Under the assumptions of time-independent and collisionless ion motion and inertialess electrons, the analytic expressions for discharge parameters are obtained as a function of the effective parameters such as effective frequency, effective current, and effective voltage. Effective parameters are determined by the ratio of two currents or voltages. Two rf sources are generally coupled to each other through the plasma medium. It is also shown that the reduction of the bulk plasma length due to the sheath size has to be considered for calculating the discharge parameters since the sheath length is not always negligible compared to the bulk plasma length. Furthermore, the dependence of discharge parameters on the low frequency is presented.
Tau functions and residues
Authors: Lee Min Ho
Published: October 2003

We consider the residues of Laurent series of several variables as well as the residues of pseudodifferential operators of several variables and establish relations between such residues and tau functions associated to pseudodifferential operators of several variables.
La–silicate gate dielectrics fabricated by solid phase reaction between La metal and SiO2 underlayers
Authors: Watanabe Heiji , Ikarashi Nobuyuki , Ito Fuminori
Published: October 2003

La-based high-k gate dielectrics were fabricated by reoxidation of thin La layers deposited on SiO2 underlayers. Interface reaction that causes metal diffusion through the oxide underlayer increases permittivity of the oxide and forms high-quality La–silicate films. We successfully fabricated ultrathin La–silicates of equivalent oxide thickness ranging from 0.75 to 1.6 nm with low-leakage current by controlling the interface solid phase reaction. We characterized degradation in the silicate film caused by electrical stressing and demonstrated the effectiveness of high-temperature annealing to improve the reliability of silicate dielectrics. Moreover, it was found that water absorption during exposure to air causes positive fixed charge in the silicate (flatband voltage shift), but degradation can be annealed out at relatively low temperatures.
Ordered structure and twin boundary of triblock copolymer/silica mesophase thin films
Authors: Ahn Chi Won , Rasing Theo , Kim Mahn Won
Published: October 2003

We have observed a twin boundary in a triblock copolymer/silica mesophase thin film, produced by spinning an acidic water-ethanol-tetraethoxysilane solution of a triblock copolymer on a hydrophilic treated silicon substrate. The highly ordered structure of the mesophase thin film is formed by ordering of self-assembled triblock copolymer micelles and was characterized with x-ray reflectivity and transmission electron microscopy. The mesophase thin film consists of a face-centered-cubic lattice and the orientation of the film surface is the {111} plane. Furthermore, a {111} twin plane is observed in the mesophase thin film.
Highly sensitive ultraviolet detector based on ZnO/LiNbO3 hybrid surface acoustic wave filter
Authors: Sharma Parmanand , Sreenivas K.
Published: October 2003

Fabrication of a highly-sensitive UV detector based on the surface-acoustic-wave (SAW) principle is reported. The output voltage of the SAW oscillator constructed with a ZnO/LiNbO3 hybrid SAW filter was found to decrease linearly with increasing UV light intensity, and a very low intensity UV light of 10 μW/cm2 was detected easily. Our results show its potential use in wireless UV measurement systems.
Photoinduced conductivity changes in carbon nanotube transistors
Authors: Shim Moonsub , Siddons Giles P.
Published: October 2003

Photoinduced conductivity changes in single-walled carbon nanotube transistors have been examined. Low-intensity ultraviolet light significantly reduces the p-channel conductance while simultaneously increasing the n-channel conductance. A combination of optical absorption and electron transport measurements reveals that these changes occur without variations in dopant concentrations. Possible sites of oxygen photodesorption and its implications on the observed electronic properties of nanotubes are considered.
Enhanced field emission from printed carbon nanotubes by mechanical surface modification
Authors: Vink T. J. , Gillies M. , Kriege J. C. , van de Laar H. W. J. J.
Published: October 2003

A method is presented where the morphology of screen printed carbon nanotube pastes is modified using an adhesive tape. In this way, the organic matrix material is preferentially removed leaving an optimal emitter surface of sparsely distributed and well-aligned carbon nanotubes. From these emitter surfaces, homogeneous emission was observed with emitter site densities of at least 104 emitters cm−2 and extracted current densities over 500 mA cm−2.
Extruded channel waveguides in a neodymium-doped lead–silicate glass for integrated optic applications
Authors: Mairaj Arshad K. , Feng Xian , Hewak Daniel W.
Published: October 2003

We report on the development of channel waveguides in a lead–silicate glass through the extrusion technique. An extruded glass slab with four imbedded fibers each with core size of 8 by 2.5 μm in the horizontal and vertical directions was manufactured. These neodymium-doped channel waveguides were in single-mode operation at 808 nm and had attenuation of 0.1 dB cm−1 at 1.06 μm. The measured F3/24 lifetime of 488 μs and emission cross section of 2.5×10−20 cm2 were in good agreement with reported values. The integration of multiple glass variants into a single compact platform is presented as a manufacturing route for complex integrated optical waveguides.
Shallow optically active structural defect in wurtzite GaN epilayers grown on stepped 4H-SiC substrates
Authors: Xu S. J. , Wang H. J. , Cheung S. H. , Li Q. , Dai X. Q. , Xie M. H. , Tong S. Y.
Published: October 2003

A number of wurtzite GaN epilayers directly grown on 4H-SiC (0001) misoriented by 0, 3.5°, 5°, 8°, and 21° with plasma-assisted molecular-beam epitaxy were optically characterized with photoluminescence and excitation spectra. An intense shallow-defect emission peak locating at energy position ∼70 meV lower than the near band edge emission peak at 3.47 eV is found in the emission spectra of the GaN films on 4H-SiC misoriented by 8° and 21°. Stacking mismatch boundaries are supposed to be the candidate causing the optical transition. Combined with the low-temperature photoluminescence excitation spectra of the films, the location of the electronic level induced by the structural defect is determined to be about 100 meV above the valence-band maximum of GaN.
Binding energy of parallel carbon nanotubes
Authors: Chen B. , Gao M. , Zuo J. M. , Qu S. , Liu B. , Huang Y.
Published: October 2003

We study the interaction between two separate carbon nanotubes that bond together by examing their geometry in transmission electron microscopy (TEM). The TEM image, in conjunction with a continuum mechanics model interpretation, provides an estimate of 0.36 nN binding energy between the two parallel carbon nanotubes. This result agrees well with the calculated binding energy using an atomistic model.
Room-temperature ultraviolet emission from GaN/AlN multiple-quantum-well heterostructures
Authors: Furis Madalina , Cartwright A. N. , Wu Hong , Schaff William J.
Published: October 2003

We investigate the photoluminescence (PL) properties of GaN/AlN multiple-quantum-well structures grown by plasma-induced molecular-beam epitaxy by time-resolved PL spectroscopy. Despite the large strain induced by the lattice mismatch between GaN and AlN, the samples exhibit strong room-temperature UV emission characterized by a nonexponential decay that varies across the PL feature. The energy corresponding to the peak of the PL spectra varies as a function of the well width, in agreement with a calculation of the electron–hole (e1h1) transition energy that includes the large piezoelectric and spontaneous polarizations existing inside the wells. The thermal quenching activation energies of the emission intensity can be identified as the donor and acceptor binding energies.
Synthesis, structure, and photoluminescence of very thin and wide alpha silicon nitride (α-Si3N4) single-crystalline nanobelts
Authors: Yin Long-Wei , Bando Yoshio , Zhu Ying-Chun , Li Yu-Bao
Published: October 2003

Large quantities of very thin and wide single-crystal alpha silicon nitride (α-Si3N4) nanobelts were synthesized by a vapor-solid thermal reaction between ammonia and silicon monoxide (SiO) without using any added catalyst. Scanning electron microscopy, high-resolution electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction were used to characterize the formed nanobelts. The single-crystal α-Si3N4 nanobelts are about 800–1200 nm in width, 20–35 nm in thickness and about several tens to several hundreds of micrometers in length. The nanobelts are perfect in structure. The nanobelts grow along [011] and [100] direction. Intense visible photoluminescence (PL) occurring on the wide and thin nanobelts over a broad spectrum ranging from 420 to 750 nm was observed. The visible PL emission is related to the inherently imperfect Si and N dangling bonds in the α-Si3N4 structure.
Examining the performance of the supply chain for potatoes in the Red River Delta using a pluralistic approach
Authors: Batt Peter J.
Published: October 2003

Using an analysis of marketing margins and the key dimensions of long‐term buyer‐seller relationships, it is possible to demonstrate that the supply chain for potatoes cultivated in the Red River Delta (Vietnam) is surprisingly efficient. While the prices paid to farmers are ultimately determined by supply and demand, the price farmers receive from traders and collector agents is influenced by tuber quality and the costs of transportation. Farmers are seldom dependent on their preferred trading partner and indicate that numerous alternative traders are available to purchase the potatoes they have harvested. While the traders similarly enjoy a strong positive relationship both with farmers and collector agents and their down‐stream customers, wholesalers report that they are much less satisfied in their exchange relationship with both the traders and the retailers. Wholesalers are more dependent on both their up‐stream and down‐stream trading partners and are more dissatisfied and less trusting of their exchange partners.
Perceptual differences in offer quality between Western Australian rock lobster exporters and Japanese rock lobster importers
Authors: Batt Peter J. , Morooka Ryuta
Published: October 2003

An empirical examination of the perceived differences in offer quality between Western Australian rock lobster exporters and their respective Japanese importers reveals that consistent quality, a willingness to provide market information and a willingness to meet importers” immediate needs were the most important variables influencing an importer's decision to purchase. While both importers and exporters agreed that delivering consistent quality was the most important variable, exporters ranked competitive price much higher than importers. This suggests that Western Australian exporters may benefit from adding greater value to their product offer by providing continuous product support, timely market information and responding better to importers' immediate needs, rather than attempting to compete on price against lower cost producers.
Presidential Character Revisited
Authors: Lyons Michael
Published: October 2003

This study attempts to bring a fresh perspective to the study of presidential personality. Critics of the personality approach doubt that personality really has much impact on presidential leadership, and they question whether the approach will contribute to the development of a presidential leadership theory. Critics also see problems with the conceptualization of personality variables in particular studies, such as James David Barber's much‐praised, much‐maligned The Presidential Character. The study proposes the use of the Myers‐Briggs Type Indicator (MBTI) to analyze the relationship between presidential personality and presidential leadership. Administered to about 1.7 million people annually by psychologists, career counselors, and business managers, the MBTI makes possible the classification of each president as one of 16 personality types, and it offers predictions about many characteristics of leadership style for each type. The study concludes with an extensive MBTI analysis of President Clinton's leadership style.
Reactions to Societal Trauma: Distress and/or Eustress
Authors: Suedfeld Peter
Published: October 2003

Social science approaches to the impact of severely stressful events on groups and communities have typically emphasized the vulnerability of affected populations and the need for intervention and assistance on their behalf. Without denying the importance of such help, this paper argues that communities—like individuals—are generally resilient and hardy. They are able to cope with widespread danger and disaster, to maintain rational and adaptive problem‐solving behaviors, and even to use the experience as a source of renewed strength. Reactions to the Great Plague of the 14th century and the aerial bombardment of cities in World War II, and the adjustment of Holocaust survivors and the Southeast Asian Boat People, are analyzed to illustrate these points.
Values and Voting
Authors: Barnea Marina F. , Schwartz Shalom H.
Published: October 2003

We examined relations of the 10 types of values in Schwartz's (1992) theory of voting. Hypotheses were generated by relating the core motivations of each value type to the ideological messages conveyed by party policies and symbols. Eight parties that ran in the 1988 Israeli elections were arrayed by judges on three ideological dimensions: classical liberalism, economic egalitarianism, state and religion. Discriminant analyses yielded a function whose coefficients for value types corresponded to hypotheses for the state and religion dimension and ordered party supporters on this dimension. After dropping religious parties, another value‐based function ordered party supporters on the classical liberalism dimension, as predicted. Both functions significantly improved the party classification of voters in a representative national sample (N=769). Economic egalitarianism, a nonsalient dimension in Israeli politics, was unrelated to values. Results suggest that all types of values may be politically relevant depending on context.
Solving nesting problems with non‐convex polygons by constraint logic programming
Authors: Carravilla M. A. , Ribeiro C. , Oliveira J. F.
Published: October 2003

In this paper an application of constraint logic programming (CLP) to the resolution of nesting problems is presented. Nesting problems are a special case of the cutting and packing problems, in which the pieces generally have non‐convex shapes. Because of their combinatorial optimization nature, nesting problems have traditionally been tackled by heuristics and in the recent past by meta‐heuristics. When trying to formulate nesting problems as linear programming models, to achieve global optimal solutions, the difficulty of dealing with the disjunction of constraints arises. On the contrary, CLP deals easily with this type of relationships among constraints. A CLP implementation for the nesting problem is described for convex and non‐convex shapes. The concept of nofit polygon is used to deal with the geometric constraints inherent to all cutting and packing problems. Computational results are presented.
The Announcement Effects of U.S. versus non‐U.S. Bank Mergers: Do They Differ?
Authors: DeLong Gayle L.
Published: October 2003

Non‐U.S. bank mergers are becoming an increasingly important part of the worldwide economic landscape. Are the market reactions to non‐U.S. bank mergers similar to the reaction in the United States? I address this question by examining abnormal returns of publicly traded partners on the announcement of forty‐one non‐U.S. bank mergers and comparing the returns with a U.S. control group. I find acquirers in non‐U.S. domestic bank mergers earn more and non‐U.S. targets earn less than their U.S. counterparts. However, for the subset of mergers in countries with relatively well‐developed stock markets, I find that partners earn similar returns.
Will Any q Do?
Authors: DaDalt Peter J. , Donaldson Jeffrey R. , Garner Jacqueline L.
Published: October 2003

We find that the relative levels of computationally costly q estimators and simple q estimators, when used as continuous variables, are affected by variations in many firm financial characteristics. In contrast, when the estimators are used as dichotomous variables, they classify the vast majority of firms identically with respect to the unit q breakpoint. Finally, we find that the computationally costly approach may induce sample‐selection bias as a result of data unavailability. Our results suggest that the simple approach is preferable except when extreme precision of the q estimate is of paramount importance and sample‐selection bias is not likely to be an issue.
The BRCT Domain Is a Phospho-Protein Binding Domain
Authors: Yu Xiaochun , Chini Claudia Christiano Silva , He Miao , Mer Georges , Chen Junjie
Published: October 2003

The carboxyl-terminal domain (BRCT) of the Breast Cancer Gene 1 (BRCA1) protein is an evolutionarily conserved module that exists in a large number of proteins from prokaryotes to eukaryotes. Although most BRCT domain–containing proteins participate in DNA-damage checkpoint or DNA-repair pathways, or both, the function of the BRCT domain is not fully understood. We show that the BRCA1 BRCT domain directly interacts with phosphorylated BRCA1-Associated Carboxyl-terminal Helicase (BACH1). This specific interaction between BRCA1 and phosphorylated BACH1 is cell cycle regulated and is required for DNA damage–induced checkpoint control during the transition from G
2
to M phase of the cell cycle. Further, we show that two other BRCT domains interact with their respective physiological partners in a phosphorylation-dependent manner. Thirteen additional BRCT domains also preferentially bind phospho-peptides rather than nonphosphorylated control peptides. These data imply that the BRCT domain is a phospho-protein binding domain involved in cell cycle control.
Experimental Models of Primitive Cellular Compartments: Encapsulation, Growth, and Division
Authors: Hanczyc Martin M. , Fujikawa Shelly M. , Szostak Jack W.
Published: October 2003

The clay montmorillonite is known to catalyze the polymerization of RNA from activated ribonucleotides. Here we report that montmorillonite accelerates the spontaneous conversion of fatty acid micelles into vesicles. Clay particles often become encapsulated in these vesicles, thus providing a pathway for the prebiotic encapsulation of catalytically active surfaces within membrane vesicles. In addition, RNA adsorbed to clay can be encapsulated within vesicles. Once formed, such vesicles can grow by incorporating fatty acid supplied as micelles and can divide without dilution of their contents by extrusion through small pores. These processes mediate vesicle replication through cycles of growth and division. The formation, growth, and division of the earliest cells may have occurred in response to similar interactions with mineral particles and inputs of material and energy.
The String Revolution Will Be Televised
Authors: Voss David
Published: October 2003

The Elegant Universe
. NOVA. WGBH Science Unit, Boston. On PBS, Tuesday evenings, 28 October (parts 1 and 2) and 4 November (part 3).
www.pbs.org/wgbh/nova/elegant/

In a three-hour miniseries full of dazzling graphics, the PBS series NOVA and Brian Greene present the claims and strangeness of string theory.
In Vitro Analysis of the Ability of
Trichophyton rubrum
To Become Resistant to Terbinafine
Authors: Osborne Colin S. , Hofbauer Bettina , Favre Bertrand , Ryder Neil S.
Published: October 2003

In this study, we have investigated in vitro the resistance frequency and development of resistance to terbinafine of
Trichophyton rubrum
. Results demonstrated that naturally occurring mutants are rare and that
T. rubrum
appears to have little capacity to develop resistance to terbinafine even after prolonged exposure.
Genetic Relatedness of Recently Collected Spanish Respiratory Tract
Streptococcus pneumoniae
Isolates with Reduced Susceptibility to Amoxicillin
Authors: Pérez-Trallero E. , Marimón J. M. , González A. , García-Rey C. , Aguilar L.
Published: October 2003

Of
Streptococcus pneumoniae
isolates from 17 hospitals, 9.8% were amoxicillin nonsusceptible (MIC ≥ 4 μg/ml). The genetic relatedness of 138 isolates was studied by pulsed-field gel electrophoresis. Although 44 different clones were detected, more than 62% of these isolates were related to four clones (Spain
23F
-1, Spain
6B
-2, Spain
9V
-3, and Spain
14
-5).
Activity of Posaconazole in Treatment of Experimental Disseminated Zygomycosis
Authors: Dannaoui Eric , Meis Jacques F. G. M. , Loebenberg David , Verweij Paul E.
Published: October 2003

Three isolates of zygomycetes were used to produce a disseminated infection in nonimmunocompromised mice. Against all zygomycete strains, amphotericin B significantly prolonged survival. Itraconazole was inactive against
Rhizopus microsporus
and
Rhizopus oryzae
but was partially active against
Absidia corymbifera
. Posaconazole had no beneficial effects against
R. oryzae
but showed partial activity against
A. corymbifera
. Posaconazole had a clear dose-response effect against
R. microsporus
.
Correlation between Pyrazinamide Activity and
pncA
Mutations in
Mycobacterium tuberculosis
Isolates in Taiwan
Authors: Huang Tsi-Shu , Lee Susan Shin-Jung , Tu Hui-Zin , Huang Wen-Kuei , Chen Yao-Shen , Huang Chung-Kai , Wann Shue-Ren , Lin Hsi-Hsun , Liu Yung-Ching
Published: October 2003

A total of 76 clinical
Mycobacterium tuberculosis
isolates from Taiwan were tested for pyrazinamidase activity, pyrazinamide susceptibility, and
pncA
mutations. Frequency of resistance to PZA rose with increases in resistance to first-line drugs. Of 17 pyrazinamide-resistant strains, 7 (3 of which had not been previously described) possessed mutations in the
pncA
gene.
Salmonella enterica
Serovar Typhimurium Expressing Mutant Lipid A with Decreased Endotoxicity Causes Maturation of Murine Dendritic Cells
Authors: Kalupahana Ruwani , Emilianus A. Romina , Maskell Duncan , Blacklaws Barbara
Published: October 2003

A major
Salmonella
component involved in cellular activation is the lipopolysaccharide (LPS) molecule which can act as a dendritic cell (DC) stimulator. The structure of the lipid A domain of the LPS molecule dictates its immunostimulatory capacity with various cell types. In this study, the role of lipid A as an integral component of
Salmonella
in stimulating murine DCs was studied by using a
Salmonella enterica
serovar Typhimurium
lpxM
mutant with defective lipid A. This study revealed that a mutation in
lpxM
did not significantly affect the ability of bacteria to activate DCs. Although the
lpxM
mutant less tumor necrosis factor alpha, interleukin-1β, and inducible nitric oxide synthase than the parental strain, this was only seen at lower multiplicities of infection (MOIs). Both strains upregulated surface molecule expression on DCs and augmented the T-cell-stimulating capacity of these cells in an MOI-independent manner. Thus, the
lpxM
mutation did not appear to affect the stimulatory capacity of the
Salmonella
mutant.
Phage Lytic Enzyme Cpl-1 as a Novel Antimicrobial for Pneumococcal Bacteremia
Authors: Loeffler Jutta M. , Djurkovic Svetolik , Fischetti Vincent A.
Published: October 2003

Streptococcus pneumoniae
is becoming increasingly antibiotic resistant worldwide, and thus new antimicrobials are badly needed. We report the use of Cpl-1, the lytic enzyme of a pneumococcal bacteriophage, as an intravenous therapy for pneumococcal bacteremia in a mouse model. A 2,000-μg dose of Cpl-1 reduced pneumococcal titers from a median of log
10
4.70 CFU/ml to undetectable levels (<log
10
2.00 CFU/ml) within 15 min. This dose given 1 h after intravenous infection led to 100% survival at 48 h, compared to the 20% survival of buffer-treated controls. In advanced bacteremia, treatment with two doses at 5 and 10 h still resulted in significantly longer survival (
P
< 0.0001) and a hazard ratio of 0.29 (95% confidence interval, 0.04 to 0.35). The enzyme is immunogenic, but the treatment efficacy was not significantly diminished after previous intravenous exposure of mice and hyperimmune rabbit serum did not neutralize the activity. Cpl-1 is also very effective as a topical nasal treatment against colonization by
S. pneumoniae
. In vitro, the enzyme is active against many serotypes of
S. pneumoniae
, independent of their penicillin resistance, and it is very specific for this species. Bacteriophage enzymes are unusual but extremely effective antimicrobials and represent a new weapon against infections with resistant bacteria.
Low-Level Pilin Expression Allows for Substantial DNA Transformation Competence in
Neisseria gonorrhoeae
Authors: Long Cynthia D. , Tobiason Deborah M. , Lazio Matthew P. , Kline Kimberly A. , Seifert H. Steven
Published: October 2003

The gonococcal pilus is a major virulence factor that has well-established roles in mediating epithelial cell adherence and DNA transformation. Gonococci expressing four gonococcal pilin variants with distinct piliation properties under control of the
lac
regulatory system were grown in different levels of the inducer isopropyl-β-
d
-thiogalactopyranoside (IPTG). These pilin variants expressed various levels of pilin message and pilin protein in response to the level of IPTG in the growth medium. Moreover, posttranslational modifications of the variant pilin proteins were detected, including S-pilin production and glycosylation. The ratio of the modified and unmodified pilin forms did not substantially change with different levels of pilin expression, showing that these modifications are not linked to pilin expression levels. DNA transformation competence was also influenced by IPTG levels in the growth medium. Substantial increases in transformation competence over an isogenic, nonpiliated mutant were observed when limited amounts of three of the pilin variants were expressed. Immunoelectron microscopy showed that when limited amounts of pilin are expressed, pili are rare and do not explain the pilin-dependent transformation competence. This pilin-dependent transformation competence required prepilin processing, the outer membrane secretin PilQ, and the twitching-motility-regulating protein PilT. These requirements show that a fully functional pilus assembly apparatus is required for DNA uptake when limited pilin is produced. We conclude that the pilus assembly apparatus functions to import DNA into the bacterial cell in a pilin-dependent manner but that extended pili are not required for transformation competence.
New Rat Model ofPneumocystisPneumonia Induced by Anti-CD4+T-Lymphocyte Antibodies
Authors: Thullen Timothy D. , Ashbaugh Alan D. , Daly Kieran R. , Linke Michael J. , Steele Paul E. , Walzer Peter D.
Published: October 2003

The CD4+T lymphocyte plays a central role in host defense againstPneumocystispneumonia but has received only limited attention in rats. CD4+T-cell-depleting (OX-38) and nondepleting (W3/25) monoclonal antibodies, which recognize an identical or adjacent epitope, were administered for up to 14 weeks to Lewis rats that had been exposed toPneumocystis. While OX-38 produced a greater decrease in circulating CD4+cells than W3/25, both antibody treatments resulted in similar effects on the health of the rats and the levels ofPneumocystispneumonia, which were milder than those found with corticosteroids. W3/25 also did not enhance the severity ofPneumocystispneumonia achieved with corticosteroids alone. We conclude that CD4+cell function is more important than CD4+cell number in host defense againstPneumocystisin the rat and that this new model permits study of opportunistic infections in the rat without the confounding effects of corticosteroids.
Role of Cytokines and Major Histocompatibility Complex Restriction in Mouse Resistance to Infection with a Natural Recombinant Strain (Type I-III) ofToxoplasma gondii
Authors: Fux Blima , Rodrigues Cibele V. , Portela Ricardo W. , Silva Neide M. , Su Chunlei , Sibley David , Vitor Ricardo W. A. , Gazzinelli Ricardo T.
Published: October 2003

Herein we characterized various genetic markers and the biological behavior of a natural recombinant strain ofToxoplasma gondii(P-Br). From nine genetic markers analyzed, three (B1,ROP1, andSAG1) and three (cS10-A6,GRA6, andSAG3) markers belong to parasites from the type I and type III lineages, respectively. TheSAG2andL363loci were shown to be type I-III chimera alleles. The cB2l-4 microsatellite marker showed a unique haplotype. The P-Br strain presented low virulence in the acute phase of infection and was cystogenic during the chronic infection. The interleukin 12/gamma interferon axis and inducible nitric oxide synthase were main determinants of resistance during the acute infection with the P-Br strain. As opposed to infection with the type II strain ofT. gondii(ME-49), peroral infection with the P-Br strain led only to a light inflammatory infiltrate and no major lesions in the intestine of the C57BL/6 mice. In addition, the BALB/c (resistant to ME-49) and C57BL/6 (susceptible to ME-49) mice were shown, respectively, to be more susceptible and more resistant to cyst formation and toxoplasmic encephalitis when infected with the P-Br strain. Further, the C57BL/KsJ and DBA2/J congenic strains containing major histocompatibility complex (MHC) haplotype “d” were more resistant than the parental strains (C57BL/6 and DBA1/J), when infected with the ME-49 but not with the P-Br strain. Together, our results indicate that resistance to cyst formation and toxoplasmic encephalitis induced during infection with P-Br is not primarily controlled by the MHC haplotype d, as previously reported for type II strains ofT. gondii.
Modulation of the Bovine Delayed-Type Hypersensitivity Responses to Defined Mycobacterial Antigens by a Synthetic Bacterial Lipopeptide
Authors: Whelan A. O. , Hope J. C. , Howard C. J. , Clifford D. , Hewinson R. G. , Vordermeier H. M.
Published: October 2003

The use of defined protein and peptide antigens can overcome specificity limitations of purified protein derivatives in the detection of bovine tuberculosis when the antigens are used in blood-based tests. Since the use of these specific antigens as skin test reagents could have practical advantages, we investigated the potential of
Mycobacterium bovis
-specific antigens to stimulate delayed-type hypersensitivity (DTH) responses in cattle experimentally infected with
M. bovis
. A cocktail of the recombinant antigens ESAT-6, MPB83, and MPB64 failed to stimulate in vivo DTH in cattle that had been experimentally infected with
M. bovis
despite the fact that the antigens were recognized in vitro by the same animals. However, it was possible to stimulate antigen-specific bovine DTH responses by using ESAT-6 in combination with a synthetic bacterial lipopeptide. This lipopeptide stimulated the release of the proinflammatory cytokine tumor necrosis factor alpha from monocyte-derived bovine dendritic cells in vitro, thereby providing a possible mechanism for its DTH-enhancing properties.
Lung Epithelial Cells and Extracellular Matrix Components Induce Expression of
Pneumocystis carinii STE20
, a Gene Complementing the Mating and Pseudohyphal Growth Defects of
ste20
Mutant Yeast
Authors: Kottom Theodore J. , Köhler Julia R. , Thomas Charles F. , Fink Gerald R. , Limper Andrew H.
Published: October 2003

Pneumocystis carinii
causes severe pneumonia in immunocompromised hosts. The binding of
P. carinii
to alveolar epithelial cells and extracellular matrix constituents such as fibronectin and vitronectin is a central feature of infection, which initiates proliferation of the organism. Herein, we demonstrate that
P. carinii
binding to lung cells specifically alters the gene expression of the organism, regulating fungal growth. Subtractive hybridization was performed to isolate
P. carinii
genes expressed following binding to mammalian extracellular matrix constituents.
P. carinii STE20
(
PCSTE20
), a gene participating in mating and pseudohyphal growth of other fungi, was identified following adherence to the extracellular matrix constituents fibronectin, vitronectin, collagen, and lung epithelial cells. The expression of
PCSTE20
and a related
P. carinii
mitogen-activated protein kinase (MAPK) kinase gene, also implicated in signaling of mating, were both specifically upregulated by binding to matrix protein. The expression of general cyclin-dependent kinases and other MAPKs not involved in mating pathways were not altered by organism binding.
PCSTE20
expression was also strongly enhanced following organism attachment to A549 lung epithelial cells. When expressed in a
Saccharomyces cerevisiae ste20Δ
mutant,
PCSTE20
suppressed defects in both mating and pseudohyphal growth. These findings are consistent with the observed proliferation and filopodial extension of
Pneumocystis
organisms adherent to the epithelium in the lungs of immunocompromised hosts.
PCSTE20
expression appears to represent a significant component in the regulation of the life cycle of this intractable opportunistic pathogen.
Comparative Pathogenicity ofEscherichia coliO157 and Intimin-Negative Non-O157 Shiga Toxin-ProducingE. coliStrains in Neonatal Pigs
Authors: Dean-Nystrom Evelyn A. , Melton-Celsa Angela R. , Pohlenz Joachim F. L. , Moon Harley W. , O'Brien Alison D.
Published: October 2003

We compared the pathogenicity of intimin-negative non-O157:H7 Shiga toxin (Stx)-producingEscherichia coli(STEC) O91:H21 and O104:H21 strains with the pathogenicity of intimin-positive O157:H7 and O157:H−strains in neonatal pigs. We also examined the role of Stx2d-activatable genes and the large hemolysin-encoding plasmid of O91:H21 strain B2F1 in the pathogenesis of STEC disease in pigs. We found that allE. colistrains that made wild-type levels of Stx caused systemic illness and histological lesions in the brain and intestinal crypts, whereas none of the control Stx-negativeE. colistrains evoked comparable central nervous system signs or intestinal lesions. By contrast, the absence of intimin, hemolysin, or motility had little impact on the overall pathogenesis of systemic disease during STEC infection. The most striking differences between pigs inoculated with non-O157 STEC strains and pigs inoculated with O157 STEC strains were the absence of attaching and effacing intestinal lesions in pigs inoculated with non-O157:H7 strains and the apparent association between the level of Stx2d-activatable toxin produced by an STEC strain and the severity of lesions.
Inhibition of Platelet Adherence to Brain Microvasculature Protects against SeverePlasmodium bergheiMalaria
Authors: Sun Guang , Chang Wun-Ling , Li Jie , Berney Seth Mark , Kimpel Donald , van der Heyde Henri C.
Published: October 2003

Some patients withPlasmodium falciparuminfections develop cerebral malaria, acute respiratory distress, and shock and ultimately die even though drug therapy has eliminated the parasite from the blood, suggesting that a systemic inflammatory response contributes to malarial pathogenesis.Plasmodium berghei-infected mice are a well-recognized model of severe malaria (experimental severe malaria [ESM]), and infected mice exhibit a systemic inflammatory response. Because platelets are proposed to contribute to ESM and other systemic inflammatory responses, we determined whether platelet adherence contributes to experimental malarial pathogenesis. Indeed, a significant (P< 0.005) increase in the number of rolling and adherent platelets was observed by intravital microscopy in brain venules ofP. berghei-infected mice compared with the number in uninfected controls. P-selectin- or ICAM-1-deficient mice exhibit increased survival afterP. bergheiinfection. We observed a significant (P< 0.0001) reduction in the morbidity of mice injected with anti-CD41 (αIIbor gpIIb) monoclonal antibody on day 1 ofP. bergheiinfection compared with the morbidity of infected controls injected with rat immunoglobulin G. Additionally, platelet rolling and adhesion in brain venules were reduced inP. bergheimice lacking either P-selectin or ICAM-1 or when the platelets were coated with anti-CD41 monoclonal antibody. Unlike other inflammatory conditions, we did not detect platelet-leukocyte interactions duringP. bergheimalaria. Because (i) leukocyte adhesion is not markedly altered in the absence of P-selectin or ICAM-1 and (ii) CD41 is not an adhesion molecule for parasitized erythrocytes, these findings support the hypothesis that inhibition of platelet adhesion to the brain microvasculature protects against development of malarial pathogenesis.
Antibodies That Inhibit
Plasmodium falciparum
Adhesion to Chondroitin Sulfate A Are Associated with Increased Birth Weight and the Gestational Age of Newborns
Authors: Duffy Patrick E. , Fried Michal
Published: October 2003

Antibodies that inhibit
Plasmodium falciparum
adhesion to the placental receptor chondroitin sulfate A are associated with a reduced risk of placental malaria, but whether these antibodies lead to improved pregnancy outcomes is unknown. We measured antiadhesion antibody levels in parturient women in western Kenya, where malaria transmission is intense. Secundigravid women with antiadhesion activity in their plasma delivered babies that were on average 398 g heavier (
P
= 0.019) and 2 weeks more mature (
P
= 0.002) than babies delivered to secundigravidas without antiadhesion activity. Our findings support the development of antiadhesion vaccines to prevent poor fetal outcomes due to pregnancy malaria.
Novel Role for Albumin in Innate Immunity: Serum Albumin Inhibits the Growth ofBlastomyces dermatitidisYeast Form In Vitro
Authors: Giles Steven , Czuprynski Charles
Published: October 2003

In this study we found that serum inhibitory activity againstBlastomyces dermatitidiswas principally mediated by albumin. This was confirmed in experiments using albumin from several mammalian species. Analbuminemic rat serum did not inhibitB.dermatitidisgrowth in vivo; however, the addition of albumin restored inhibitory activity. Inhibitory activity does not require albumin domain III and appears to involve binding of a low-molecular-weight yeast-derived growth factor.
Secretion of theorgCGene Product bySalmonella entericaSerovar Typhimurium
Authors: Day James B. , Lee Catherine A.
Published: October 2003

HilA activates the transcription of genes onSalmonellapathogenicity island 1 (SPI1), which encodes a type III secretion system (TTSS). Previous studies showed that transposon insertions inorgC, a gene located on SPI1, increasehilAexpression. We characterize theorgCgene product and show that it is secreted via the SPI1 TTSS. We propose a model whereby OrgC functions as a secreted repressor of the SPI1 virulence genes.