bluuebunny/crossref_metadata_2025 huggingface dataset:
Composite-layered solid-state field controlled emitter for a better control of the cathode surface barrier
Authors: Semet V. , Binh Vu Thien , Zhang J. P. , Yang J. , Khan M. Asif , Tsu R.
Published: April 2005

Experimental measurements have shown that electron emission was obtained from metallic planar surfaces covered with ultrathin wide band gap semiconductor layers. To get a better control of the effective surface barrier, we proposed a composite-layer nanostructured solid-state field controlled emitter with two ultrathin layers of 4nm GaN and 2nm Al0.5Ga0.5N. This composite structure defined a quantum well at the cathode surface. The threshold of the applied field to obtain electron emission was in the range of 100V∕μm. To interpret these experimental results, we propose a dual-barrier model related to the nanostructured layers and a serial two-step mechanism for the electron emission. In a first step, under the polarization, the electrons are injected into the ultrathin surface layer from the cathode substrate, creating a concentration of electrons in the GaN quantum well. This electron concentration or space charge formation induced an energy shift leading to a relative lowering of the vacuum level compared to the Fermi level of the substrate. We have measured the electron emission dependence with field and temperature of these cathodes and have determined an effective surface tunnelling barrier ⩽0.5eV consistent with an effective thermal activation energy of ∼0.85eV. Estimation of the effective barrier due to space charge formation from to the occupation of the localized bands in the quantum well is in good agreement with the experimental data.
Effect of electric field on chemical bonds of carbon-doped silicon oxide as evidenced by in situ Fourier transform infrared spectroscopy
Authors: Yiang K. Y. , Yoo W. J. , Krishnamoorthy Ahila
Published: April 2005

In this study, we use in situ Fourier transform infrared (FTIR) spectroscopy on a carbon-doped silicon oxide (SiOCH) to determine the origins of its lower breakdown strength (compared to SiO2) and the precursors of dielectric breakdown. While subjecting the SiOCH film to externally applied electric fields, the FTIR spectra are recorded. Changes in peak area ratios and intensities are determined and correlated to field-induced perturbation of chemical bonds in SiOCH. This is a potentially powerful technique which provides new insights into the dielectric degradation and breakdown phenomena.
Approach to interface roughness of silicide thin films by micro-Raman imaging
Authors: Zhao F. F. , Sun W. X. , Feng Y. P. , Zheng J. Z. , Shen Z. X. , Pang C. H. , Chan L. H.
Published: April 2005

The rough interface between a silicide film and a Si substrate induces large junction leakage currents in Si-based devices. In this work, we demonstrate that micro-Raman imaging can be used to characterize the interface roughness, without any special sample preparation. Pure metal (Ni and Ti) thin films and the subsequently formed silicide thin films after annealing (NiSi and TiSi2) were investigated using the intensity of the Si Raman band at 520cm−1. Uniformity results of the pure metal films are in good agreement with those obtained using global four-point-probe measurement. In comparison, the signals obtained from the interfaces between Si and NiSi are nonuniform with large variations. The intensity of the major peak of NiSi at 214cm−1 shows a point-to-point correlation with the intensity of the Si peak at 520cm−1, which reveals that the local grain orientation affects the diffusion velocity of Ni atoms and the growth of NiSi. Images of Ti-silicides show that the interface of the C49 TiSi2 phase is much smoother than that of the C54 TiSi2 phase which is due to different formation mechanisms. Simulation was carried out based on two interfacial models, a two-step interface and a sinusoidal interface, to understand the correlation between the average attenuation of the Si Raman signal and the film thickness.
Rutile films grown by molecular beam epitaxy on GaN and AlGaN∕GaN
Authors: Hansen P. J. , Vaithyanathan V. , Wu Y. , Mates T. , Heikman S. , Mishra U. K. , York R. A. , Schlom D. G. , Speck J. S.
Published: April 2005

Titanium dioxide (TiO2, with the rutile structure) was grown on (0001) oriented GaN and (0001) Al0.33Ga0.67N∕GaN heterostructure field effect transistor (HFET) structures by molecular beam epitaxy. X-ray diffraction showed (100)TiO2‖(0001)GaN(AlGaN) and [001]TiO2‖⟨112¯0⟩GaN(AlGaN) with three rotational variants of the TiO2. Transmission electron microscopy of 50nm thick TiO2 films on GaN and AlGaN∕GaN showed sharp interfaces with no intermixing or reaction between the oxide and semiconductor. The TiO2 exhibited a columnar film microstructure with a lateral domain size of a few nanometers parallel to (101)TiO2 and a few tens of nanometers parallel to (101¯)TiO2. Metal–oxide HFETs with 50nm thick TiO2 dielectric layers under the gate were processed and compared to HFETs without the TiO2 dielectric layer. The transconductance of the HFETs with TiO2 was 140mS∕mm, approximately 20% less than HFETs with no dielecric, and the pinchoff voltages of the two stuctures were comparable. The dielectric constant of the TiO2 was ∼70. The gate leakage current of the HFETs with TiO2, ∼4×10−6mA∕mm at 50V, was approximately 4 orders of magnitude lower than that of the HFETs with no dielectric. Band offset measurements were performed using x-ray photoelectron spectroscopy, and the valence band of the rutile TiO2 and the GaN nearly line up.
Influence of gas atmosphere during laser surface treatment of CNT cathode
Authors: Rochanachirapar W. , Murakami K. , Yamasaki N. , Abo S. , Wakaya F. , Takai M. , Hosono A. , Okuda S.
Published: April 2005

An ultraviolet laser was used to irradiate the screen-printed carbon nanotube (CNT) cathodes in air, N2, and O2 atmospheres in various pressures. The emission current density of CNT cathodes at a field of 6.6V∕μm was increased by a factor of 400 after laser irradiation in an O2 atmosphere, which was enhanced by the increase in O2 pressure. On the other hand, N2 has less influence on the laser irradiation effect. The enhancement in electron emission by laser irradiation in air was found to be 20% of that in an O2 atmosphere with the same pressure, because of the partial pressure of the oxygen in air.
Evaluation of the effectiveness of H2 plasmas in removing boron from Si after etching of HfO2 films in BCl3 plasmas
Authors: Wang C. , Donnelly V. M.
Published: April 2005

Etching of high dielectric constant (“high-k”) materials in BCl3-containing plasmas leaves behind a boron residue on underlying Si or SiO2 surfaces during the over-etching period. Boron is a p-type dopant and therefore it is best if it is removed prior to subsequent processing. We have investigated the effectiveness of H2 plasmas in removing this boron-containing layer. Following etching of HfO2 thin films in a high-density BCl3 plasma, including a 60 s overetch period, samples were transferred under vacuum to a UHV chamber equipped with x-ray photoelectron spectroscopy (XPS). After observing areal density B-coverages of ∼1×1015cm−2 (equivalent of ∼1monolayer), the samples were transferred back to the plasma reactor for exposure to the H2 cleaning plasma, and then reexamined by XPS. Optical emission spectroscopy was used to monitor B deposition on and removal from the plasma chamber walls. B deposition on the reactor walls during BCl3 plasma exposure reached saturated coverage in ∼2min. Following this, the H2 plasma removed half of the B on the walls in 90 s and 90% in 320 s. B was rapidly removed (<5s) from BCl3 plasma over-etched Si surfaces provided that the walls were first cleaned in the H2 plasma, with the Si sample held in the UHV chamber during the chamber cleaning process. Conversely, it took much longer (∼180s) to remove all detectable B on the sample surface if the sample and the reactor chamber walls were cleaned in the H2 plasma at the same time. Apparently B is transported from the walls to the Si surface in this latter case. Etching rates of 22 and 1700Å∕min were measured for SiO2 and Si, respectively, in the H2 cleaning plasma. The fast etching of Si allows still shorter cleaning times, or preferably dilute H2 plasmas to be effective in removing B with less Si removal, provided the chamber walls are first cleaned in an H2 plasma.
Fabrication and field emission characteristics of high density carbon nanotube microarrays
Authors: Chuang C. C. , Huang J. H. , Lee C. C. , Chang Y. Y.
Published: April 2005

High density carbon nanotube field emitter arrays (CNT-FEAs) with various multilayer cathode structures have been fabricated on Si utilizing conventional integrated circuit technology and microwave-heated chemical vapor deposition process. The CNT-FEAs were configured as triode emitters with 1-μm thermal SiO2 as the insulator and 400-nm Cr as the gate, and compared per the resulting morphologies, Raman spectra, and field emission characteristics. It was found that the Ni∕Cr∕Si cathode structure is the best fit for selective growth of CNTs in gate holes. In particular, a CNT-FEA fabricated on Ni(60nm)∕Cr(80nm)∕Si cathode structure has yielded excellent emission characteristics, with low turn-on and threshold fields, being, respectively, at 0.45 and 3.7V∕μm. This triode CNT device also exhibited a uniform image of high brightness(∼1800cd∕m2) on a green-phosphor coated idium-tin-oxide glass and a relatively stable emission current, being tested at a constant anode voltage of 1000 and 900 V, respectively.
High current field emission from carbon nanofiber films grown using electroplated Ni catalyst
Authors: Park Kyung Ho , Yim Jong Hyuk , Lee Soonil , Koh Ken Ha
Published: April 2005

Carbon nanofibers (CNFs) with various structures were synthesized using electroplated nickel catalysts on diverse metal buffer layers via hot-filament chemical-vapor-deposition method. High-density thick CNFs were grown on copper and gold buffer layers whereas low-density thin CNFs were grown on chromium and titanium buffer layers. All CNFs revealed solid structure without hollow cores, and graphitic platelets of CNFs consisted of a mixed structure of stacked and herringbone arrangement. CNF films grown on gold buffer layers showed high-emission-current density and temporal stability: 170mA∕cm2 at 7.3V∕μm, and 10.3% fluctuation over 10 h at the current density of 6mA∕cm2, respectively.
X-ray generation from large area carbon-based field emitters
Authors: Busta H. , Lesiak S. , Zwicker B. , Montgomery J. , Wan Z. , Feinerman A.
Published: April 2005

Cylindrical-shaped graphite field emitters with total emission areas of about 100 and 800cm2 were used to construct an x-ray source in which the anode consists of a 107 cm long quartz tube, 7.7 cm outer diameter, and a wall thickness of 0.4 cm. Except for the end portions, the tube is coated with a 5μm Cu film. The emitter surface is 0.35 cm separated from the quartz tube. Electrons originating from the emitter surface impinge upon the copper film and some of them are converted into x rays. The x rays penetrating the quartz tube can be utilized for irradiation experiments where ionizing radiation is desirable. X-ray spectra, photon count rate, and dose rate were measured, as well as current-voltage characteristics of the two field emitter configurations. Within the “hot” zone of the 5 and 30.5 cm long emitter regions, the dose is uniform within ±20% in the lateral direction and ±20% along the inner surface of the quartz tube. (The “hot” zone is defined as the region where the x rays are generated). It was established that the photon count and the dose scale proportional with the emission current and increase exponentially with target voltage. The x-ray source was operated to 42.5 kV at a pressure of 5×10−7Torr.
Effect of thermal annealing on emission characteristics of nanoelectron source fabricated using beam-assisted process
Authors: Murakami K. , Yamasaki N. , Abo S. , Wakaya F. , Takai M.
Published: April 2005

The thermal annealing effects on a single-field emitter fabricated by beam-assisted processing were investigated from the viewpoint of the leakage current between the gate and cathode. The cathode current of the field emitters before annealing did not show a linear dependence in Fowler–Nordheim (FN) plots due to the leakage current. However, the current showed a linear dependence in FN plots at and above 200 °C. Thermal annealing increased the emission efficiency. The maximum efficiency was almost 100% after annealing at 750 °C. The percentage of working nanoelectron sources was also increased by annealing T⩾500°C. The postannealing is effective in reducing the leakage current of the field emitters because of the removal of contaminants arising from the beam-induced process.
Gas-assisted focused ion beam etching characteristics of niobium
Authors: Fu X. L. , Li P. G. , Jin A. Z. , Zhang H. Y. , Yang H. F. , Tang W. H.
Published: April 2005

The gas-assisted focused ion beam etching characteristics of niobium have been investigated systematically in I2 and XeF2 gas atmosphere, respectively. The effects of the etching parameters, such as: ion beam current, dwell time, overlap percentage and gas species, on the niobium etching rate and on the gas-assisted etching enhancement have been studied. It was found that the overlap percentage had little effect on the etching characteristics of niobium. It also showed that the I2 radicals are more reactant with niobium than XeF2 radicals, and to obtain maximum improvement from the gas-assisted etching process one needs to select a smaller ion beam current with a shorter beam dwell time.
Combined in situ and ex situ analysis of hydrogen radical and thermal removal of native oxides from (001) GaAs
Authors: Eyink Kurt G. , Grazulis Larry
Published: April 2005

We are currently involved in the study of regrowth of InAs on nanopatterned GaAs surfaces. The nanopatterning is accomplished through the movement of the sample while in contact with a diamond tip maintained at a constant load. Native oxides present on these surfaces introduce an obstacle to the subsequent regrowth. Therefore, the removal of this oxide is a prerequisite step for the study of the subsequent regrowth on these patterned surfaces. In this study we used in situ spectroscopic ellipsometry (SE) and reflection high energy electron diffraction (RHEED) as well as ex situ atomic force microscopy to follow the hydrogen cleaning and thermal removal of the native oxides from the GaAs surface. SE and RHEED were used to follow the oxide desorption process in situ and were used to determine when the surface was clean. Post AFM analysis indicated that the thermally desorbed oxide surface contained pits which were approximately 100 Å deep and covered 15% of the surface. Hydrogen radical cleaning was studied at substrate temperatures between 400–535 °C using a pressure of approximately 1×10−6Torr and a cracking thermocouple reading of 900 °C. The time to produce a clean surface was found to decrease as the temperature was increased. At the highest temperatures, cleaning took less than 10 min. AFM analysis indicated smooth surfaces were produced up to 500 °C. Above 500 °C, pitting was seen to occur similar to that observed for thermal oxide desorption. It was found that the onset of this pitting coincided with time at which spectroscopic ellipsometry indicated a change in the oxide layer.
Electronic defect states at annealed metal∕4H–SiC interfaces
Authors: Tumakha S. , Goss S. H. , Brillson L. J. , Okojie R. S.
Published: April 2005

We have used low energy electron-excited nanoscale luminescence spectroscopy (LEEN) to study the formation of electronic surface states at metal∕4H–SiC contacts. These junctions were formed using both low and high reactivity metals to study how the nature of interface chemical bonding affects the interface state formation. We observe evidence for the formation and removal of localized states at energies that have been associated with morphological SiC defects. Metals such as Au and Ag with no strong chemical reactivity exhibited the most pronounced changes. Conversely, chemically-reactive metals such as Ti and Ni exhibited only minor changes and only with high temperature annealing. These observations suggest that native defects rather then metal-specific chemical bonding dominate the interface electronic features.
Microstructure and mechanical properties of superhard Ti–B–C–N films deposited by dc unbalanced magnetron sputtering
Authors: Park In-Wook , Kim Kwang Ho , Kunrath Augusto O. , Zhong Dalong , Moore John J. , Voevodin A. A. , Levashov E. A.
Published: April 2005

Superhard quarternary Ti–B–C–N films were successfully deposited on AISI 304 stainless steel substrates by a dc unbalanced magnetron sputtering technique from a Ti–B–C composite target. The relationship between microstructures and mechanical properties was investigated in terms of the nanosized crystallites∕amorphous system. The synthesized Ti–B–C–N films were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). These analyses revealed that our Ti–B–C–N films are composites of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous boron nitride (BN) phase including some of carbon, CNx, B2O3 components. The hardness of the Ti–B–C–N films increased with the increase of N content up to a maximum value of approximately 45 GPa at 10 at. % N, with a subsequent decrease in hardness at higher N content. This value is considerably higher than the hardness measured in our Ti–B–C films (∼35GPa). The Ti–B–C–N(10 at .%) film also showed the highest H3∕E*2 value (∼1.7GPa) among the coatings produced. A systematic investigation of the microstructures and mechanical properties of Ti–B–C–N films prepared with various N contents is reported in this paper.
Energy distributions of field emission electrons from silicon emitters
Authors: Shimawaki Hidetaka , Suzuki Yousuke , Sagae Katsumi , Neo Yoichiro , Mimura Hidenori
Published: April 2005

The energy distributions of field-emitted electrons from single-tip n type and p type Si field emitters have been analyzed. The energy distributions of both n type and p type Si emitters show a single peak, and the peak position shifts slightly towards the low energy side in the n type emitter as the gate voltage is increased. In the case of the p type emitter a considerably larger shift towards lower energies is observed. The distributions from the n type emitter have the same threshold energies near the Fermi level energy and become broader with the increase in the gate voltage. On the other hand, the threshold energies of the p type emitter are more than 1.5eV below the Fermi level and shift to the lower energy side as well as the peak position in the energy distribution with increasing the gate voltage. In addition, the energy distributions of the p type emitter are considerably broad in comparison with those of the n type emitter, but the full width half maximums (FWHMs) of the distributions do not significantly change with the increase in the gate voltage. These results suggest that for the n type Si field emitter electrons are basically supplied from the Si conduction band and are emitted from the neighborhood of the conduction band under the effect of the band bending and electron trapping in surface and oxide states at the interfaces of the emitter. On the other hand, for the p type Si field emitter, electrons are mainly emitted through the interface states supplied from the valence band of Si.
A Simple Laboratory Experiment to Measure e/k
Authors: Inman Fred
Published: April 2005

The measurement of fundamental constants is common practice in instructional laboratories. A number of the equipment manufacturers have developed apparatus for such applications, e.g., the determination of e by the Millikan oil drop method or the determination of the speed of light with fiber optics. Other experiments determine not a single constant, but a combination of constants, e.g., e/m by electron beam deflection in a magnetic field or h/e by the photoelectric effect. About 30 years ago Carl E. Miller and I1 proposed a method of measuring e/k, the ratio of the electron charge to Boltzmann's constant, that was reasonably simple but not necessarily inexpensive because it involved the use of a sensitive electrometer. In recent years, however, inexpensive digital multimeters (DMM), many costing less than $30, have found their way into the physics laboratory. The purpose of this paper is to suggest the use of two DMMs, one operating as a voltmeter and the other as an ammeter, in a simple circuit involving a junction transistor and a variable potential source. Even the potential source can be quite simple, a 1.5-V battery and a 1-kΩ potentiometer, as shown in Fig. 1. If available, a variable dc power supply replacing the battery and potentiometer would be more convenient.
Collaborative Competition? A Great Way to Teach and Motivate
Authors: Romanello Tony
Published: April 2005

In my physics classes, I strive to motivate my students to do their very best work and inspire them to work harder than they have ever been asked to before. To reach that level, I find that my students need an outside motivation. They need to have someone from outside of their education community judge their skills and efforts. I have found that participation in team competitions provides students with the motivation to excel and also has the benefits of teaching students to work in a team setting. Thanks to several science-oriented organizations, there are a number of what I like to call “collaborative competitions” just begging for our students to enter, compete, and yes, even win! In this paper, I will describe some of the competitions my students have participated in and provide some tips for other teachers who may want to do likewise.
Projectile Motion Without Trigonometric Functions
Authors: Mohazzabi Pirooz , Kohneh Zahra A.
Published: April 2005

In this paper we provide a treatment of projectile motion that is accessible to students who are unfamiliar with trigonometry but do have a minimal knowledge of elementary algebra and know the Pythagorean theorem. In this approach, we view the initial velocity of the projectile as being a combination of a vertical part (component) v0V and a horizontal component v0H (see Fig. 1). This is in contrast to the usual approach of taking the initial speed v0 and the launch angle as being given. We let the initial position be the origin and neglect air drag. Assuming that the constant acceleration kinematics equations are known, we may write vH = v0H, and the horizontal distance traveled is x = v0H t, where t is the elapsed time. We also have vV = v0V − gt, where g is the magnitude of the acceleration due to gravity. And the vertical displacement is y = v0V t − ½ gt2. These equations may be used to find the location and velocity of the projectile at any time t. We can also find the equation of the path of the projectile by combining Eq. [1(b)] and Eq. [2(b)] to get y = −(g2v0H2) x2 + (v0Vv0H) x, which is the equation of a concave-down parabola.
Physics for Poets?
Authors: Graf Erlend H.
Published: April 2005

“Slowly the hour-hand of the clock moves round; So slowly that no human eye hath power To see it move …!”1
Learning to Listen to What Your Students Say
Authors: Blanton Patricia
Published: April 2005

Have you worked for hours on your lectures yet feel you were the only one listening when you delivered them? (The snoring from the back of the room was your first clue.) Have you lamented your frustration when your assessments show the students did not develop a good understanding of the concept about which you delivered that brilliant lecture? (Students cry, “You never gave us a problem like that!”) Have you spent hours developing demonstrations only to find that students remember the demo but not the concept you were trying to illustrate? (“I remember that you didn't get hurt on that bed of nails but I don't remember why.”) The lecture format that you experienced throughout most of your education just is not working for most of the learners in your classroom. It's your turn to be the one helping others to understand, and you are struggling with identifying techniques that work.
Characterization of a Cluster of Three Glycosyltransferase Enzymes Essential for
Moraxella catarrhalis
Lipooligosaccharide Assembly
Authors: Edwards Katie J. , Allen Simon , Gibson Bradford W. , Campagnari Anthony A.
Published: April 2005

Moraxella catarrhalis
isolates express lipooligosaccharide (LOS) molecules on their surface, which share epitopes similar to that of the
Neisseria
and
Haemophilus
species. These common LOS epitopes have been implicated in various steps of pathogenesis for the different organisms. In this study, a cluster of three LOS glycosyltransferase genes (
lgt
) were identified in
M. catarrhalis
7169, a strain that produces a serotype B LOS. Mutants in these glycosyltransferase genes were constructed, and the resulting LOS phenotypes were consistent with varying degrees of truncation compared to wild-type LOS. The LOS structures of each
lgt
mutant were no longer detected by a monoclonal antibody (MAb 4G5) specific to a highly conserved terminal epitope nor by a monoclonal antibody (MAb 3F7) specific to the serotype B LOS side chain. Mass spectrometry of the LOS glycoforms assembled by two of these
lgt
mutants indicated that
lgt1
encodes an α(1-2) glucosyltransferase and the
lgt2
encodes a β(1-4) galactosyltransferase. However, these structural studies could not delineate the function for
lgt3
. Therefore,
M. catarrhalis lgt3
was introduced into a defined β(1-4) glucosyltransferase
Haemophilus ducreyi
35000glu− mutant in
trans
, and monoclonal antibody analysis confirmed that Lgt3 complemented the LOS defect. These data suggest that
lgt3
encodes a glucosyltransferase involved in the addition of a β(1-4)-linked glucose to the inner core. Furthermore, we conclude that this enzymatic step is essential for the assembly of the complete LOS glycoform expressed by
M. catarrhalis
7169.
Characterization of PmfR, the Transcriptional Activator of the pAO1-Borne
purU-mabO-folD
Operon of
Arthrobacter nicotinovorans
Authors: Chiribau Calin B. , Sandu Cristinel , Igloi Gabor L. , Brandsch Roderich
Published: April 2005

Nicotine catabolism by
Arthrobacter nicotinovorans
is linked to the presence of the megaplasmid pAO1. Genes involved in this catabolic pathway are arranged on the plasmid into gene modules according to function. During nicotine degradation γ-
N
-methylaminobutyrate is formed from the pyrrolidine ring of nicotine. Analysis of the pAO1 open reading frames (ORF) resulted in identification of the gene encoding a demethylating γ-
N
-methylaminobutyrate oxidase (
mabO
). This gene was shown to form an operon with
purU-
and
folD
-like genes. Only in bacteria grown in the presence of nicotine could transcripts of the
purU-mabO-folD
operon be detected, demonstrating that this operon constitutes part of the pAO1 nicotine regulon. Its transcriptional start site was determined by primer extension analysis. Transcription of the operon was shown to be controlled by a new transcriptional regulator, PmfR, the product of a gene that is transcribed divergently from the
purU
,
mabO
, and
folD
genes. PmfR was purified, and electromobility shift assays and DNase I-nuclease digestion experiments were used to determine that its DNA binding site is located between −48 and −88 nucleotides upstream of the transcriptional start site of the operon. Disruption of
pmfR
by homologous recombination with a chloramphenicol resistance cassette demonstrated that PmfR acts in vivo as a transcriptional activator. Mutagenesis of the PmfR target DNA suggested that the sequence GTTT-14 bp-AAAC is the core binding site of the regulator upstream of the −35 promoter region of the
purU-mabO-folD
operon.
Phosphorylation-Independent Activity of Atypical Response Regulators ofHelicobacter pylori
Authors: Schär Jennifer , Sickmann Albert , Beier Dagmar
Published: April 2005

The genome of the gastric pathogenHelicobacter pyloriharbors a remarkably low number of regulatory genes, including three and five open reading frames encoding two-component histidine kinases and response regulators, respectively, which are putatively involved in transcriptional regulation. Two of the response regulator genes, hp1043 and hp166, proved to be essential for cell growth, and inactivation of the response regulator gene hp1021 resulted in a severe growth defect, as indicated by a small-colony phenotype. The sequences of the receiver domains of response regulators HP1043 and HP1021 differ from the consensus sequence of the acidic pocket of the receiver domain which is involved in the phosphotransfer reaction from the histidine kinase to the response regulator. Using a genetic complementation system, we demonstrated that the function of response regulator HP166, which is essential for cell growth, can be provided by a mutated derivative carrying a D52N substitution at the site of phosphorylation. We found that the atypical receiver sequences of HP1043 and HP1021 are not crucial for the function of these response regulators. Phosphorylation of the receiver domains of HP1043 and HP1021 is not needed for response regulator function and may not occur at all. Thus, the phosphorylation-independent action of these regulators differs from the well-established two-component paradigm.
Isolation of Lactococcal Prolate Phage-Phage Recombinants by an Enrichment Strategy Reveals Two Novel Host Range Determinants
Authors: Rakonjac Jasna , O'Toole Paul W. , Lubbers Mark
Published: April 2005

Virulent lactococcal prolate (or c2-like) phages are the second most common phage group that causes fermentation failure in the dairy industry. We have mapped two host range determinants in two lactococcal prolate phages, c2 and 923, for the host strains MG1363 and 112. Each phage replicates on only one of the two host strains: c2 on MG1363 and 923 on 112. Phage-phage recombinants that replicated on both strains were isolated by a new method that does not require direct selection but rather employs an enrichment protocol. After initial mixed infection of strain 112, two rotations, the first of which was carried out on strain MG1363 and the second on 112, permitted continuous amplification of double-plating recombinants while rendering one of the parent phages unamplified in each of the two rotations. Mapping of the recombination endpoints showed that the presence of the N-terminal two-thirds of the tail protein L10 of phage c2 and a 1,562-bp
cosR
-terminal fragment of phage 923 genome overcame blocks of infection in strains MG1363 and 112, respectively. Both infection inhibition mechanisms act at the stage of DNA entry; in strain MG1363, the infection block acts early, before phage DNA enters the cytoplasm, and in strain 112, it acts late, after most of the DNA has entered the cell but before it undergoes
cos
-end ligation. These are the first reported host range determinants in bacteriophage of lactic acid bacteria required for overcoming inhibition of infection at the stage of DNA entry and
cos
-end ligation.
Staphylococcus intermedius
Produces a Functional
agr
Autoinducing Peptide Containing a Cyclic Lactone
Authors: Ji Guangyong , Pei Wuhong , Zhang Linsheng , Qiu Rongde , Lin Jianqun , Benito Yvonne , Lina Gerard , Novick Richard P.
Published: April 2005

The
agr
system is a global regulator of accessory functions in staphylococci, including genes encoding exoproteins involved in virulence. The
agr
locus contains a two-component signal transduction module that is activated by an autoinducing peptide (AIP) encoded within the
agr
locus and is conserved throughout the genus. The AIP has an unusual partially cyclic structure that is essential for function and that, in all but one case, involves an internal thiolactone bond between a conserved cysteine and the C-terminal carboxyl group. The exceptional case is a strain of
Staphylococcus intermedius
that has a serine in place of the conserved cysteine. We demonstrate here that the
S. intermedius
AIP is processed by the
S. intermedius
AgrB protein to generate a cyclic lactone, that it is an autoinducer as well as a cross-inhibitor, and that all of five other
S. intermedius
strains examined also produce serine-containing AIPs.
The Active Site of
O-
Acetylserine Sulfhydrylase Is the Anchor Point for Bienzyme Complex Formation with Serine Acetyltransferase
Authors: Huang Bin , Vetting Matthew W. , Roderick Steven L.
Published: April 2005

The biosynthesis of cysteine in bacteria and plants is carried out by a two-step pathway, catalyzed by serine acetyltransferase (SAT) and
O
-acetylserine sulfhydrylase (OASS;
O-
acetylserine [thiol] lyase). The aerobic form of OASS forms a tight bienzyme complex with SAT in vivo, termed cysteine synthase. We have determined the crystal structure of OASS in complex with a C-terminal peptide of SAT required for bienzyme complex formation. The binding site of the peptide is at the active site of OASS, and its C-terminal carboxyl group occupies the same anion binding pocket as the α-carboxylate of the
O
-acetylserine substrate of OASS. These results explain the partial inhibition of OASS by SAT on complex formation as well as the competitive dissociation of the complex by
O
-acetylserine.
Multistress Regulation inEscherichia coli: Expression ofosmBInvolves Two Independent Promoters Responding either to σSor to the RcsCDB His-Asp Phosphorelay
Authors: Boulanger Alice , Francez-Charlot Anne , Conter Annie , Castanié-Cornet Marie-Pierre , Cam Kaymeuang , Gutierrez Claude
Published: April 2005

Transcription of theEscherichia coli osmBgene is induced by several stress conditions.osmBis expressed from two promoters,osmBp1andosmBp2. The downstream promoter,osmBp2, is induced after osmotic shock or upon entry into stationary phase in a σS-dependent manner. The upstream promoter,osmBp1, is independent of σSand is activated by RcsB, the response regulator of the His-Asp phosphorelay signal transduction system RcsCDB. RcsB is responsible for the induction ofosmBp1following treatment with chlorpromazine. Activation ofosmBp1by RcsB requires a sequence upstream of its −35 element similar to the RcsB binding site consensus, suggesting a direct regulatory role.osmBappears as another example of a multistress-responsive gene whose transcription involves both a σS-dependent promoter and a second one independent of σSbut controlled by stress-specific transcription factors.
Arc and resistance welding and tumours of the endocrine glands: a Swedish case-control study with focus on extremely low frequency magnetic fields
Authors: Håkansson N , Stenlund C , Gustavsson P , Johansen C , Floderus B
Published: April 2005

Background:Mechanisms for potential effects of extremely low frequency (ELF) magnetic fields on carcinogenesis have not been identified. A potential pathway could be an interaction with the endocrine system.

Aims:To analyse occupational exposure to ELF magnetic fields from welding, and tumours of the endocrine glands.

Methods:This case-control study was based on a cohort with an increased prevalence of high exposed individuals. A total of 174 incident cases of tumours of the endocrine glands, 1985–94, were identified and data were obtained from 140 (80%) of these cases; 1692 controls frequency matched on sex and age were selected, and information on 1306 (77%) individuals was obtained. A short questionnaire was sent to a work administrator at the workplaces of the cases and controls. The exposure assessment was based on questions about job tasks, exposure to different types of welding, and exposure to solvents.

Results:There was an overall increased risk for all tumours of the endocrine glands for individuals who had been welding sometime during the follow up. The increased risk was attributable to arc welding; for resistance welding there was no clear evidence of an association. We found an increased risk for the adrenal glands in relation to arc welding, and for the parathyroid glands in relation to both arc welding and resistance welding. An imprecise increase in risk was also noted for tumours of the pituitary gland for arc welding. No confounding effect was found for solvent exposure, and there was no sign of biological interaction.

Conclusion:The increased risks of endocrine gland tumours related to welding might be explained by exposure to high levels of ELF magnetic fields.
Occupation and risk of stomach cancer in Poland
Authors: Krstev S , Dosemeci M , Lissowska J , Chow W-H , Zatonski W , Ward M H
Published: April 2005

Background:In spite of the dramatic decline in the incidence of stomach cancer in the twentieth century, Poland has one of the highest rates in the world.

Aims:To evaluate the risk of stomach cancer by grouped occupations and industries, as well as by some specific occupational exposures.

Methods:Cases (n = 443) were newly diagnosed with stomach adenocarcinomas between 1994 and 1996. Controls (n = 479) were randomly selected from the general population in Warsaw.

Results:Only a few occupations and industries were associated with significantly increased risks of stomach cancer. The most suggestive finding was for work in the leather goods industry. Risk was also significantly increased among men working in fabricated metal production and among women ever employed as managers and governmental officials. Men ever employed as teaching professionals and women employed as technical and science professionals had significantly decreased risks of stomach cancer. Among men, a significant positive trend in risk with duration of employment was observed for work in the leather industry and special trade construction. No significantly increased risks were observed for specific exposures assessed by a job-exposure matrix or by self-reports. However among men there were non-significantly increased risks with 10 or more years exposure to asbestos, metal dust, and nitrosamines assessed by a job-exposure matrix.

Conclusions:Employment in the leather goods industry, special trade construction, and metal fabrication was associated with an increased risk of stomach cancer among men. However, there were only weak associations with specific exposures. Occupational exposures do not contribute substantially to the high rates of stomach cancer in Poland.
Poisson regression analysis of ungrouped data
Authors: Loomis D , Richardson D B , Elliott L
Published: April 2005

Background:Poisson regression is routinely used for analysis of epidemiological data from studies of large occupational cohorts. It is typically implemented as a grouped method of data analysis in which all exposure and covariate information is categorised and person-time and events are tabulated.

Aims:To describe an alternative approach to Poisson regression analysis using single units of person-time without grouping.

Methods:Data for simulated and empirical cohorts were analysed by Poisson regression. In analyses of simulated data, effect estimates derived via Poisson regression without grouping were compared to those obtained under proportional hazards regression. Analyses of empirical data for a cohort of 138 900 electrical workers were used to illustrate how the ungrouped approach may be applied in analyses of actual occupational cohorts.

Results:Using simulated data, Poisson regression analyses of ungrouped person-time data yield results equivalent to those obtained via proportional hazards regression: the results of both methods gave unbiased estimates of the “true” association specified for the simulation. Analyses of empirical data confirm that grouped and ungrouped analyses provide identical results when the same models are specified. However, bias may arise when exposure-response trends are estimated via Poisson regression analyses in which exposure scores, such as category means or midpoints, are assigned to grouped data.

Conclusions:Poisson regression analysis of ungrouped person-time data is a useful tool that can avoid bias associated with categorising exposure data and assigning exposure scores, and facilitate direct assessment of the consequences of exposure categorisation and score assignment on regression results.
A FUNCTION MODEL-BASED APPROACH TO DEVELOP A MICRO-TITER TRAY MANUFACTURING AUTOMATION SYSTEM FOR DNA MICROARRAY FABRICATION
Authors: ZHANG MINGJUN , FISHER WILLIAM , SITTE HANS , TARN TZYH-JONG
Published: April 2005

This paper proposes a function model-based approach to develop manufacturing automation systems. Methods for manufacturing automation system integration and main function component design based on a function model are discussed. System cost and main function component optimization are performed in the early design stage to find low risk cost-effective solutions. To illustrate the idea, the proposed approach has been applied to a simple example of designing a flexible micro-titer tray manufacturing automation system used to fabricate DNA microarrays.
Hyperacute Diffusion-Weighted Imaging Abnormalities in Transient Ischemic Attack Patients Signify Irreversible Ischemic Infarction
Authors: Inatomi Yuichiro , Kimura Kazumi , Yonehara Toshiro , Fujioka Shodo , Uchino Makoto
Published: April 2005

Background: To characterize the frequency and clinical features of diffusion-weighted imaging (DWI) abnormalities in the hyperacute phase of transient ischemic attacks (TIAs). Methods: We performed DWI in 21 consecutive patients with TIA (mean age 64 years; 17 men and 4 women) during both the hyperacute phase (within 6 h after onset) and subacute phase (within 2–9 days after onset). Results: DWI abnormalities were present in the hyperacute phase in 11 patients (positive group) and absent in the other 10 patients (negative group). These groups could not be differentiated based on the clinical characteristics. In the subacute phase, all 11 patients from the positive group had abnormalities on MRI including T2-weighted and fluid attenuation inversion recovery images as well as DWI, with lesions being located in regions similar to those observed in the hyperacute phase. Of the 10 patients in the negative group, new DWI abnormalities were noted in 2 during the subacute phase. Conclusions: Approximately half of TIA patients in whom MRI was performed in the hyperacute phase had DWI abnormalities, all of which persisted in the subacute phase. The findings suggest that essentially all hyperacute DWI abnormalities in TIA patients may indicate irreversibility and signify the presence of brain infarction.
Mouse Models of Colorectal Cancer and Liver Metastases
Authors: Heijstek M.W. , Kranenburg O. , Borel Rinkes I.H.M.
Published: April 2005

Colorectal cancer (CRC) is one of the most common malignancies in the western world. Its high mortality rates are particularly related to the occurrence of liver metastases. Many mouse models have been developed to evaluate the various features of CRC in human. Since none of the existing mouse models mimics all the characteristics of human CRC, it is of crucial importance that the optimal model is chosen for each experiment to resolve a specific experimental question. Currently used mouse models for CRC include chemically induced CRC models, genetically engineered mouse models and models in which colon tumors are implanted in recipient mice. Recently, conditional mouse models have been created in which a gene of interest can be (in)activated in a time- and tissue-specific manner. All models have their advantages and limitations. This review highlights the most commonly used mouse models for CRC and its liver metastases, their usefulness and shortcomings, as well as recent improvements, particularly regarding intravital (tumor) imaging.
Weight Gain in the First Week of Life and Overweight in Adulthood
Authors: Stettler Nicolas , Stallings Virginia A. , Troxel Andrea B. , Zhao Jing , Schinnar Rita , Nelson Steven E. , Ziegler Ekhard E. , Strom Brian L.
Published: April 2005

Background—

Successful prevention of obesity and related cardiovascular risk factors requires a clear understanding of its determinants over the life course. Rapid infancy weight gain is associated with childhood obesity, whereas low infancy weight is associated with coronary heart disease. Our aim was to identify during which periods in infancy weight gain is associated with adult obesity.

Methods and Results—

A cohort of European American formula-fed subjects, measured on 7 occasions during infancy as part of several infant formula studies, were contacted at age 20 to 32 years, when they reported usual adult weight and height. A life-course plot was used to identify critical periods of weight gain associated with adulthood overweight (body mass index ≥25 kg/m
2
). These associations were tested with logistic regressions. Data were available for 653 subjects (72% of eligible subjects). Approximately 32% of them were overweight adults. The period between birth and age 8 days was identified as potentially critical. After adjustment for important confounding factors, weight gain during the first week of life was associated with adulthood overweight status (OR for each 100-g increase 1.28, 95% CI 1.08 to 1.52), as was weight gain during the first 112 days of life (OR 1.04, 95% CI 1.01 to 1.08). Similar results were obtained after standardization with
z
scores from a reference population.

Conclusions—

In formula-fed infants, weight gain during the first week of life may be a critical determinant for the development of obesity several decades later. These results contribute to the understanding of chronic disease programming and suggest new approaches to obesity prevention.
Characterization of hydraulic properties of rocks using probability of fluid-induced microearthquakes
Authors: Shapiro Serge A. , Rentsch Susanne , Rothert Elmar
Published: April 2005

The use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs. Such injections often induce small-magnitude earthquakes. The nature of processes leading to triggering of such microseismicity is still not completely understood. Here, we consider induced microseismicity, using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight-gas sandstone reservoir. In all three cases, we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks. This strongly supports the hypothesis of seismicity triggered by pore pressure. Moreover, this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision.
Future Vaccine Development at NICHD
Authors: ROBBINS JOHN B. , SCHNEERSON RACHEL
Published: April 2005

Abstract: Using published data and the results of our studies, we hypothesized that a critical level of serum IgG antibodies to the surface structures of invasive pathogens (capsular polysaccharides of Haemophilus influenzae type b, pneumococcus, meningococcus, Salmonella typhi, Escherichia coli, and Staphylococcus aureus, the O‐specific polysaccharide LPS domain of the LPS of Shigella, non‐typhoidal Salmonella, and E. coli, and the capsular polypeptide of Bacillus anthraces) confer immunity to these pathogens. Covalent attachment to a protein increases their immunogenicity and bestows T‐cell properties to these antigens. We have also shown that a critical level of serum IgG antibodies to pertussis toxin alone induces immunity on both an individual and on a community basis (herd immunity) to Bordetella pertussis. It is likely that all the above conjugates and pertussis toxoid will be incorporated into vaccines for routine infant immunization.
Role of Growth Factors in the Nervous System
Authors: BLACK IRA B.
Published: April 2005

Abstract: We are studying brain and stem cell plasticity. How do brain, mind, and cell change with environmental alteration? Combining molecular biology, cell culture, single cell electrophysiology, synaptic physiology, and whole animal experimentation, we have found that experience alters function.
Lessons from the Technology of Skill Formation
Authors: HECKMAN JAMES J.
Published: April 2005

Abstract: This paper discusses recent advances in our understanding of differences in human abilities and skills, their sources, and their evolution over the lifecycle.