bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic and dip resist development processes for 50 nm device fabrication
Authors: Lee K. L. , Bucchignano J. , Gelorme J. , Viswanathan R.
Published: July 2002

A comparison between the conventional dip development process and resist development with ultrasonic agitation at 40 kHz has been conducted for the development of high-resolution resist nanostructures with dimension down to 50 nm. High-resolution commercially available ZEP520 positive electron resist and an in-house epoxy-based negative resist were used in the study. For large area exposure with ultrasonic agitation for resist development, improved resist sensitivity (≈4%) over a dip development process was observed for positive resist and no sensitivity improvement was seen with negative resist. There was also no observable improvement in the measured resist contrast for both positive and negative resist with and without ultrasonic agitation. For resist development in dense arrays or isolated nanostructures, ultrasonic agitation for positive and negative resist development offered faster development rate, more uniformity in resist development and a larger window for exposure dose variation in resist nanostructures. For negative resist, it was also observed that the descum rate with ultrasonic agitation was more than a factor of 3 faster than for dip development. Experiments on the relative merits of ultrasonic agitation for resist development with cavitation at 25 kHz and a narrowly focused acoustic beam at 400 kHz indicated that faster development rate and resist contrast were obtained with cavitation for the experimental conditions used.
Differential charge detection for quantum-dot cellular automata
Authors: Amlani Islamshah , Orlov Alexei O. , Snider Gregory L. , Bernstein Gary H.
Published: July 2002

We report direct measurements of the charging diagram of a nanoscale series double-dot system at low temperatures. Our device consists of four metal dots, with two of them in series forming a double-dot, and the other two serving as electrometers for the double-dot system. This configuration allows us to externally detect all possible charge transitions within a double-dot system. Specifically, we can detect charge redistribution in the double-dot, which corresponds to shift of an electron between two dots, using differential signal from the two electrometers. We discuss possible applications as an output stage for quantum-dot cellular automata architecture.
Fabrication of a silicon-vacuum field-emission microdiode with a moving anode
Authors: Bruschi P. , Diligenti A. , Iani F. , Nannini A. , Piotto M.
Published: July 2002

A vacuum microdiode with a moving anode was fabricated by means of a new process requiring only two mask levels and only one critical etching step. The cathode, with a pyramidal shape, was made by anisotropically etching p silicon through a mask formed by the anode itself, which, at the end of the process, consists of a SiO2 suspended membrane supporting an Al layer. The process is compatible with standard complementary metal-oxide-semiconductor technology. I–V characteristics were measured under vacuum verifying also that the diode current is sensitive to visible light irradiation and to changes of the anode-to-cathode distance. A minimum anode-cathode distance of about 5000 Å was obtained.
Performance of laser ablated, laser annealed BN emitters deposited on polycrystalline diamond
Authors: Busta Heinz H. , Pryor Roger W.
Published: July 2002

Thin BN films of about 100 nm were deposited on 25 μm thick n-type polycrystalline diamond by laser ablation and annealed with a 25 ns pulse from an excimer laser at 0.1 J. Current densities of about 2 A/cm2 were obtained with an extraction electrode probe area of 2×10−3 cm2 (500 μm diameter). Emission is governed by a Fowler–Nordheim-type behavior with some deviation at higher currents due to the voltage dependency of the BN resistance. From present experiments it cannot be deduced if the films exhibit negative electron affinity. Emission currents are stable and independent of pressure to about 10−4 Torr. The magnitude of the current fluctuations are similar to Spindt-type devices. Compared to Mo and Si emitters, no careful high vacuum conditioning procedure is needed prior to operation. At current densities above 1 A/cm2, restructuring of the emission area took place at some locations of the 0.5 cm × 1 cm sample, leaving craters in the diamond substrate. After restructuring, emission still took place with modified current–voltage characteristics. Based on these results, carbon-doped BN has the potential for creating very rugged, low noise, high current density cold electron sources.
Economic and technical case for ion projection lithography
Authors: Berry I. L.
Published: July 2002

For more than a decade, technical arguments have been used to predict the demise of optical lithography. Recently economic arguments are being used, dramatically increasing the likelihood of the predictions coming true. Presently four technologies are competing to replace optical lithography. This article will describe the current state-of-the-art in ion projection lithography, and contrast its advantages and disadvantages with respect to the other nonoptical technologies. An argument will be made that ion projection lithography, uniquely, offers the possibility of reducing the dramatically escalating costs of lithography, resulting in overall lower integrated circuit production costs. This potential for reduced production costs is the prime motivator to consider ion projection lithography as a production lithography candidate.
Direct writing of active loads by focused ion beams
Authors: Wiemann C. , Versen M. , Wieck A. D.
Published: July 2002

With a 100 nm focus of a focused Ga+ ion beam with 100 keV, we write insulating lines in electronic layers of In0.21Ga0.79As quantum wells. In this way, in-plane-gate (IPG) transistors are formed which can be operated at room temperature. In a typical integration application of a common source circuit, the pull-up resistance represents a serious problem due to the high geometric aspect ratio necessary for it. For example, the typical specific sheet resistivity of the In0.19Ga0.79As quantum well of 1.2 kΩ needs to be increased to 100 kΩ by a 1 μm wide, about 83 μm long channel. In order to save this waste of area we introduce active loads in the form of a narrow channel. In this way, the pull-up resistor requires orders of magnitude less area and stabilizes the drain current due to velocity saturation, leading to lower supply voltages. Inverters in this technology are presented and characterized. In finite element simulations these circuits are further investigated. The operation of these systems is based on the lateral depletion of adjacent quantum well areas. The basic differences between depletion within pn half spaces and pn half planes are discussed analytically, showing a marked dependence on dimensionality. In particular, it is shown that the ruggedness of IPGs can be explained by these phenomena.
Growth of strained GaInP on InP by metalorganic molecular beam epitaxy for heterostructure field effect transistor application
Authors: Cohen G. M. , Zisman P. , Bahir G. , Ritter D.
Published: July 2002

The crystalline quality of tensile strained Ga0.25In0.75P layers grown on InP substrates was investigated. The samples were grown by metalorganic molecular beam epitaxy. Little or no relaxation was found in Ga0.25In0.75P layers which were up to 500 Å thick. The relaxation of layers less than 700 Å thick was isotropic, but thicker (bulk-like) layers relaxed anisotropically, with the main relaxation along the [11̄0] direction. Fully strained layers up to a thickness of 650 Å were obtained by employing strain compensation. Heterostructure field effect transistors (HFETs) incorporating a tensile 200 Å thick Ga0.25In0.75P barrier were fabricated. A composite channel of compressive strained Ga0.3In0.7As and lattice matched GaInAs was used to compensate the tensile strained barrier. The HFET channel was partially doped. A peak transconductance of 200 mS/mm was obtained in HFETs having a 1 μm long gate. The drain-source breakdown voltage was 10 V, and gate-drain breakdown voltage was 11 V. The unity current gain frequency, fT, and the maximum frequency of oscillation, fmax, were 23.5 and 50 GHz, respectively. Resonant tunneling diodes with Ga0.25In0.75P barriers and a Ga0.47In0.53As well were demonstrated as well. Peak to valley current ratios of 1.15 and 5 were obtained at room temperature and 77 K, respectively.
Red luminescence from a focused ion beam modified silicon surface
Authors: Erickson L. E. , Schmuki P. , Lockwood D. J.
Published: July 2002

We present a new principle and technique that can be used to create light emitting porous silicon submicron patterns of arbitrary shape on silicon wafers. We demonstrate that porous silicon growth can be preferentially initiated at surface defects created by maskless focused ion beam implantation into n-type silicon. During electrochemical polarization, the implanted areas show a significantly lower threshold potential for pore formation than the nonimplanted areas [0.25 V vs 3.8 V standard calomel electrode (SCE)]. For samples electrochemically polarized at potentials below 3.8 V SCE, implanted areas show the typical red-orange photoluminescence of porous silicon while the areas that are not implanted show only the band gap infrared photoluminescence from silicon.
Vapor deposition polymerization of 4-fluorostyrene and pentafluorostyrene
Authors: Bartlett B. , Buckley L. J. , Godbey D. J. , Schroeder M. J. , Fontenot C. , Eisinger S.
Published: July 2002

Solventless deposition of thin, uniform dielectric films is of considerable interest and importance in the microelectronics industry due to environmental concerns and increasing wafer sizes. This work demonstrates a solvent-free method for atmospheric pressure chemical vapor deposition polymerization of thin films on a variety of substrates, including silicon, molybdenum, platinum and copper. Polymerization of 4-fluorostyrene (4FS) and pentafluorostyrene (PFS) is used as a model system. Depth profiling is performed using x-ray photoelectron spectroscopy, ellipsometry, and step profilometry. Film growth is found to be independent of substrate, and proceeds with activation energies of 14±1 and 15±1 kcal/mol, respectively, for 4FS and PFS deposition between 425 and 550 K. Films are shown by gel permeation chromatography to consist of low molecular weight polymer and oligimer species (between 3 and ∼140 repeat units). Atomic force microscopy analysis of films grown by this method indicates that the root mean square thickness variation along the surface is about 2.5%.
Room-temperature radio frequency sputtered Ta2O5: A new etch mask for bulk silicon dissolved processes
Authors: Chu A. K. , Huang Y. S. , Tang S. H.
Published: July 2002

A new etch mask, namely tantalum pentoxide (Ta2O5), has been prepared for bulk silicon dissolved processes. The Ta2O5 thin films were formed at room temperature by a magnetron radio frequency sputtering technique on both sides of a double side polished 4 in. silicon wafer. Patterns were then formed on the substrate using a dielectric lift-off technique. The silicon wafer was then etched in a mixture of ethylenediamine, pyrocatechol, and water (EDP) until the exposed region of the substrate was completely removed. The thickness of the Ta2O5 thin films ranged from 100 to 700 and nm were tested as the etch masks. The etching temperature of the EDP was kept at 120 °C and the etching time was over 4 h. After etching, the surface morphology of the deposited films deteriorates with increasing etching time in EDP. The maximum roughness measured for wafers deposited with 500 nm thick Ta2O5 were 3.8±0.5 and 8.2±0.5 nm before and after EDP etch, respectively. This room-temperature technology can be used for applications in Si microelectromechanical systems and is compatible with standard indegrated circuit fabrication technology.
Advances in field emission displays phosphors
Authors: Holloway P. H. , Trottier T. A. , Abrams B. , Kondoleon C. , Jones S. L. , Sebastian J. S. , Thomes W. J. , Swart Hendrik
Published: July 2002

Recent advances in the phosphors used for field emission displays (FEDs) are discussed. After reviewing the range of voltages and phosphors being used in first generation devices, the improved properties of future generation phosphors are reviewed. Specifically, next generation displays will require better low voltage efficiencies, chromaticity, saturation behavior, and maintenance. Possible routes to achieve these improvements are discussed. The improved understanding of the role of charging and surface recombination effects on cathodoluminescent intensity and efficiency is reviewed. An improved understanding of electron beam-stimulated surface chemical reaction effects on the degradation of phosphor is presented. It is concluded that recent research efforts have created a new level of understanding of FED phosphors, and this should lead to the necessary improvements in properties.
Resistive arc protection for field-emitter-array cold cathodes used in X-band inductive output amplifiers
Authors: Parameswaran L. , Harris C. T. , Graves C. A. , Murphy R. A. , Hollis M. A.
Published: July 2002

Field emitter arrays (FEAs) can provide advantages over gridded thermionic emitters when used as cold cathodes in inductive output amplifier (IOA) tubes. However, they are prone to destructive arcing currents that reduce their lifetime. Display developers have alleviated this problem by means of integral resistors formed in series with the emitting tips, but the resistive layers as currently used preclude gate modulation at X-band frequencies. By using a vertical instead of a lateral resistor, the layer can act as its own bypass capacitor under high frequency operation. An analysis of the effect of the resistive layer on rf performance is given. It is shown that reducing the thickness of the layer results in an acceptable bypass capacitor value, while still maintaining sufficient arc current protection. This is confirmed by means of an analytical model and SPICE simulation of a resistively protected FEA in an IOA configuration. FEAs fabricated with such resistive layers showed improvements in lifetime under dc test conditions.
Fabrication and characterization of chromium based single-electron transistors with evaporated chromium oxide barrier tunnel junctions
Authors: Pashkin Yu. A. , Pekola J. P. , Kuzmin L. S.
Published: July 2002

We fabricated chromium based single-electron transistors comprising small-area Cr/CrOx/Cr tunnel junctions with an evaporated chromium oxide barrier. The transistors are fabricated using e-beam lithography with a bilayer resist and two-angle shadow evaporation. We describe the fabrication process and discuss the device characteristics.
Multilayer resist films applicable to nanopatterning of insulating substrates based on current-injecting scanning probe lithography
Authors: Sugimura Hiroyuki , Takai Osamu , Nakagiri Nobuyuki
Published: July 2002

Scanning probe lithography based on localized current injection using the probe tip of atomic force microscopy (AFM) has been applied to nanoprocessing of an insulating substrate. An electrically conductive resist film composed of triple layers was developed for this current-injecting AFM lithography. The bottom layer of the resist, which served as a current pass during patterning, consisted of amorphous silicon (a-Si) with 20 nm in thickness prepared by ion-beam sputtering. An organosilane monolayer, that is, octadecylsilyl self-assembled monolayer (ODS-SAM) of 2 nm in thickness, was used as the top layer of the resist, therefore, as the imaging layer in which nanoscale patterns were drawn by AFM. In order to bind the a-Si and the ODS-SAM together, the intermediate layer of the resist, that is, Si oxide of 2 nm in thickness, was prepared by photooxidation of the a-Si layer. Through an AFM-lithographic process using this multilayered resist, nanofabrication of fine grooves on a Si oxide substrate was demonstrated. The minimum feature size about 50 nm was successfully fabricated.
Control of photogenerated acid diffusion and evaporation by copolymerization with a basic monomer
Authors: Kim Jin-Baek , Kwon Young-Gil , Choi Jae-Hak , Jung Min-Ho
Published: July 2002

Copolymers of t-butyl methacrylate and 3-(t-butoxycarbonyl)-1-vinylcaprolactam (BCVC) were synthesized with various monomer feed ratios. Diffusion of photogenerated acid in the copolymer films and the acid trapping capability of the basic BCVC units were investigated. The evaporation of acid was also studied by a spectral change of an indicator film that consisted of poly(vinyl alcohol) and tetrabromophenol blue sodium salt. It is found that only acid surviving deactivation by the BCVC units diffuses into unexposed areas and evaporates from the copolymer film. The evaporation of a low molecular weight basic additive is also examined. Whereas the low molecular weight basic additive is evaporated during baking, the basic monomer units in the copolymer are not evaporated at all. Thus, the copolymer with the basic monomer can control the acid diffusion and evaporation effectively. The new resist system enables us to form fine patterns even after a 2 h postexposure delay without any additional treatment.
Liquid immersion deep-ultraviolet interferometric lithography
Authors: Hoffnagle J. A. , Hinsberg W. D. , Sanchez M. , Houle F. A.
Published: July 2002

An apparatus for deep-ultraviolet interferometric lithography is described, in which the interfering beams illuminate the substrate through a fused silica prism and a layer of index-matching liquid. The liquid-immersion technique was found to be compatible with a commercially available, chemically amplified photoresist. The apparatus was used with a 257 nm light source to write gratings having a period of 97 nm and linewidth of approximately 40 nm.
Measuring acid generation efficiency in chemically amplified resists with all three beams
Authors: Szmanda Charles R. , Brainard Robert L. , Mackevich Joseph F. , Awaji Akira , Tanaka Tsutomu , Yamada Yutaka , Bohland John , Tedesco Serge , Dal’Zotto Bernard , Bruenger Wilhelm , Torkler Michael , Fallmann Wolfgang , Loeschner Hans , Kaesmaier Rainer , Nealey Paul M. , Pawloski Adam R.
Published: July 2002

A method for measuring acid generation efficiency is presented and utilized to determine the relative efficiency of four photoacid generators (PAGs) upon radiation with photon, electron, and ion beams. In this method, chemically amplified resists are prepared with varying amounts of base, coated into thin films (1000 Å), and exposed. Linear plots of the base concentration against the threshold exposure dose for each resist yield the threshold acid concentration and the acid generation rate constant for each PAG. The acid-generating efficiency of the four PAGs (ND-Tf, TPS-Tf, TBI-PFOS, and TBI-Tf) upon irradiation with DUV (248 nm), EUV (13.4 nm), x-ray (1 nm), e beam (30 and 50 keV), and He+ ions is evaluated.
Novel mask-wafer gap measurement scheme with nanometer-level detectivity
Authors: Moon Euclid E. , Everett Patrick N. , Meinhold Mitchell W. , Mondol Mark K. , Smith Henry I.
Published: July 2002

We describe a means of measuring the gap between mask and substrate in an x-ray lithography system. The method does not require that the gap be scanned. The method encodes the gap in the spatial phase, spatial frequency, and separation of sets of interference fringes. The fringes result from the diffraction from a checkerboard on the mask, with constant period in one direction and varying period in the transverse direction. The separation of fringe sets gives an unambiguous measure of gap when the mask is approaching the substrate, from 400 to 30 μm. At the smaller gaps used for exposure, checkerboards with different chirp periods are utilized to indicate the gap without ambiguity. The phases of the fringes as a function of gap were calibrated with a Fabry-Pérot interferometer. The repeatability of the phases between consecutive scans of gap was found to have a 5 nm standard deviation. This method of measuring gap may prove useful in a variety of applications that require a controlled gap between two plates.
Topography of skeletal muscle ryanodine receptors studied by atomic force microscopy
Authors: Wei Q.-Q. , Chen S.-F. , Cheng X.-Y. , Yu X.-B. , Hu J. , Li M.-Q. , Zhu P. H.
Published: July 2002

Tapping mode atomic force microscopy (AFM) was used to investigate the topography of isolated ryanodine receptors of rabbit skeletal muscle (RyR1) both in air and in a buffer. In air, images fourfold symmetric in appearance were obtained. Two different configurations could be distinguished in the AFM topography of single RyR1s, depending on whether there was a center protrusion. In the buffer, even though square images of RyR1s were discerned, the detailed topography of RyR1 appeared different from that in air. Possible reasons for this are discussed.
Estimation of emission field and emission site of boron-doped diamond thin-film field emitters
Authors: Gotoh Y. , Kondo T. , Nagao M. , Tsuji H. , Ishikawa J. , Hayashi K. , Kobashi K.
Published: July 2002

The electric field required to emit electrons for boron-doped diamond together with the emission site was estimated using measurement systems that can precisely control the emitter–collector gap and lateral position. Three different types of field emitters were prepared by microwave plasma chemical vapor deposition. Type A was a typical diamond film on a flat silicon substrate, type B was a heteroepitaxial diamond film that was deposited on a (111) oriented platinum substrate, and type C was a pyramidal diamond film fabricated by the transfer mold method. For all the emitters, the voltage required to extract 0.2 nA was measured as a function of the emitter–collector gap, where the device of the emitter–collector configuration is approximated by a pair of parallel plates. The results showed that a strong electric field was applied in front of the emitter. For type B, the emission current distribution was measured by a device in which the collector was an etched needle. It was found that the emission current was concentrated at some points, which would be the crystallite edge, and also that, even at a flat crystal facet, electrons were emitted by applying a similar electric field. A similar result was obtained for type C emitters. This study revealed that the electron can be emitted from any position on the film, but generally the crystallite edge is the most probable emission site due to the concentration of a high electric field there compared to other places on the film.
The Ti LMM Auger Spectrum of a Titanium Hydride Film
Authors: Lisowski Wojciech , van den Berg Albert H. J.
Published: July 2002

We present Auger spectra of titanium hydride (TiHy) and titanium films, covered by ultrathin gold layers. The TiHy films were obtained due to hydrogen interaction with the Ti film deposited in situ onto a Pyrex glass substrate under UHV conditions. Both Ti and TiHy films were then covered in situ by a nanoscale Au layer. The Auger analyses were performed in separate systems. Analysis of the features of the Ti Auger spectra during the sputter profile measurements allow the TiHy to be distinguished and characterized in the bulk region of the Au/TiHy layer.
The Elusive Hydroxyl Revisited
Authors: Brune William
Published: July 2002

The hydroxyl radical (OH) is an important oxidant in Earth's atmosphere, but measurement of its minuscule abundance is very difficult. In his Perspective, Brune provides an updated look at recent measurements carried out in Germany in which two different techniques were compared.
Identification of Maize Histone Deacetylase HD2 as an Acidic Nucleolar Phosphoprotein
Authors: Lusser Alexandra , Brosch Gerald , Loidl Adele , Haas Hubertus , Loidl Peter
Published: July 2002

The steady state of histone acetylation is established and maintained by multiple histone acetyltransferases and deacetylases, and this steady state affects chromatin structure and function. The identification of a maize complementary DNA encoding the chromatin-bound deacetylase HD2 is reported. This protein was not homologous to the yeast
RPD3
transcriptional regulator. It was expressed throughout embryo germination in correlation with the proliferative activity of cells. Antibodies against recombinant HD2-p39 immunoprecipitated the native enzyme complex, which was composed of phosphorylated p39 subunits. Immunofluorescence microscopy and sequence homologies suggested nucleolar localization. HD2 is an acidic nucleolar phosphoprotein that might regulate ribosomal chromatin structure and function.
Platinum-Group Element Abundance Patterns in Different Mantle Environments
Authors: Rehkämper Mark , Halliday Alex N. , Barfod Dan , Fitton J. Godfrey , Dawson J. Barry
Published: July 2002

Mantle-derived xenoliths from the Cameroon Line and northern Tanzania display differences in their platinum-group element (PGE) abundance patterns. The Cameroon Line lherzolites have uniform PGE patterns indicating a homogeneous upper mantle over several hundreds of kilometers, with approximately chondritic PGE ratios. The PGE patterns of the Tanzanian peridotites are similar to the PGE systematics of ultramafic rocks from ophiolites. The differences can be explained if the northern Tanzanian lithosphere developed in a fluid-rich suprasubduction zone environment, whereas the Cameroon Line lithosphere only experienced melt extraction from anhydrous peridotites.
Large-Cage Zeolite Structures with Multidimensional 12-Ring Channels
Authors: Bu Xianhui , Feng Pingyun , Stucky Galen D.
Published: July 2002

Zeolite type structures with large cages interconnected by multidimensional 12-ring (rings of 12 tetrahedrally coordinated atoms) channels have been synthesized; more than a dozen large-pore materials were created in three different topologies with aluminum (or gallium), cobalt (or manganese, magnesium, or zinc), and phosphorus at the tetrahedral coordination sites. Tetragonal UCSB-8 has an unusually large cage built from 64 tetrahedral atoms and connected by an orthogonal channel system with 12-ring apertures in two dimensions and 8-ring apertures in the third. Rhombohedral UCSB-10 and hexagonal UCSB-6 are structurally related to faujasite and its hexagonal polymorph, respectively, and have large cages connected by 12-ring channels in all three dimensions.
Electromechanical Properties of an Ultrathin Layer of Directionally Aligned Helical Polypeptides
Authors: Jaworek T. , Neher D. , Wegner G. , Wieringa R. H. , Schouten A. J.
Published: July 2002

The electromechanical properties of a monomolecular film of poly-γ-benzyl-
l
-glutamate (PBLG) 15 nanometers thick grafted at the carboxyl-terminal end to a flat aluminum surface were measured. The field-induced change in film thickness, dominated by a large inverse-piezoelectric effect, demonstrates that the “grafting-from” technique forces the chains into a parallel arrangement. The mechanical plate modulus of the film as determined by electrostriction agrees with the theoretical prediction for a single PBLG molecule along the chain axis. The experiments show that ultrathin polypeptide layers with large persistent polarization can be fabricated by the grafting approach.
Dimerization-Induced Inhibition of Receptor Protein Tyrosine Phosphatase Function Through an Inhibitory Wedge
Authors: Majeti Ravindra , Bilwes Alexandrine M. , Noel Joseph P. , Hunter Tony , Weiss Arthur
Published: July 2002

The function and regulation of the receptorlike transmembrane protein tyrosine phosphatases (RPTPs) are not well understood. Ligand-induced dimerization inhibited the function of the epidermal growth factor receptor (EGFR)–RPTP CD45 chimera (EGFR-CD45) in T cell signal transduction. Properties of mutated EGFR-CD45 chimeras supported a general model for the regulation of RPTPs, derived from the crystal structure of the RPTPα membrane-proximal phosphatase domain. The phosphatase domain apparently forms a symmetrical dimer in which the catalytic site of one molecule is blocked by specific contacts with a wedge from the other.
Three-Dimensional Deformation Measured in an Alaskan Glacier
Authors: Harper Joel T. , Humphrey Neil F. , Pfeffer W. Tad
Published: July 2002

Measurements of movement along 28 boreholes reveal the three-dimensional flow field in a 6 million cubic meter reach of Worthington Glacier, a temperate valley glacier located in Alaska. Sliding at the bed accounted for 60 to 70 percent of the glacier's surface motion. Strain rates in the ice were low from the surface to a depth of about 120 meters, but then increased rapidly toward the bed. Ice deformation was not affected by temporal changes in the sliding rate. The three-dimensional pattern of motion indicates that plane strain, which is often assumed by models, is a poor approximation of this viscous flow.
Optical Properties of an Ionic-Type Phononic Crystal
Authors: Lu Yan-qing , Zhu Yong-yuan , Chen Yan-feng , Zhu Shi-ning , Ming Nai-ben , Feng Yi-Jun
Published: July 2002

An ionic-type phononic crystal composed of two ferroelectric media with opposite spontaneous polarization aligned periodically in a superlattice structure was studied theoretically and experimentally. The coupling between vibrations of the superlattice and the electromagnetic waves results in various long-wavelength optical properties, such as microwave absorption, dielectric abnormality, and polariton excitation, that exist originally in ionic crystals. The results show that this artificial crystal structure can be used to simulate the microscopic physical processes in real crystals.
Experimental Studies of Extinction Dynamics
Authors: Belovsky Gary E. , Mellison Chad , Larson Chad , Van Zandt Peter A.
Published: July 2002

Extinction of populations occurs naturally, but global extinction rates are accelerating, making understanding extinction a high priority for conservation. Extinction in experimental populations of brine shrimp (
Artemia franciscana
) was measured to assess hypothesized extinction processes. Greater initial population size, greater maximum population size supported by the environment, and lower variation in environmental conditions reduced the likelihood of extinction, as hypothesized. However, initial population size was less important, and maximum population size and environmental variation were more important than often hypothesized. Unexpectedly, deterministic oscillations in population size due to inherent nonlinear dynamics and overcrowding were as important or more important than hypothesized processes.
Identification and Analysis of Bacterial Protein Secretion Inhibitors Utilizing a SecA-LacZ Reporter Fusion System
Authors: Alksne L. E. , Burgio P. , Hu W. , Feld B. , Singh M. P. , Tuckman M. , Petersen P. J. , Labthavikul P. , McGlynn M. , Barbieri L. , McDonald L. , Bradford P. , Dushin R. G. , Rothstein D. , Projan S. J.
Published: July 2002

Protein secretion is an essential process for bacterial growth, yet there are few if any antimicrobial agents which inhibit secretion. An in vivo, high-throughput screen to detect secretion inhibitors was developed based on the translational autoregulation of one of the central protein components, SecA. The assay makes use of a SecA-LacZ fusion reporter construct in
Escherichia coli
which is induced when secretion is perturbed. Several compounds, including two natural product extracts, which had the ability to induce the reporter fusion were identified and the MICs of these compounds for
Staphylococcus aureus
strain MN8 were found to be ≤128 μg/ml. Enzyme-linked immunosorbent assay, Western blotting, and immunoprecipitation techniques were used to analyze the affects of these compounds on protein secretion. Six representative compounds presented here appear to be bona fide secretion inhibitors but were found to have deleterious effects on membranes. It was concluded that, while the method described here for identifying inhibitors of secretion is valid, screens such as this, which are directed against the membrane-bound portion of a pathway, may preferentially identify compounds which affect membrane integrity.
Sequences of the NPS-1 and TLE-1 β-Lactamase Genes
Authors: Pai Hyunjoo , Jacoby George A.
Published: July 2002

The NPS-1 and TLE-1 β-lactamase genes were cloned and sequenced. NPS-1 differed from LCR-1 β-lactamase in 8 of 260 amino acids. TLE-1 differed from TEM-1 by a single Asp(115)→Gly substitution and has been renamed TEM-90.
Overproduction and Biochemical Characterization of the
Chryseobacterium meningosepticum
BlaB Metallo-β-Lactamase
Authors: Vessillier Sandrine , Docquier Jean-Denis , Rival Sandrine , Frere Jean-Marie , Galleni Moreno , Amicosante Gianfranco , Rossolini Gian Maria , Franceschini Nicola
Published: July 2002

The BlaB metallo-β-lactamase of
Chryseobacterium meningosepticum
CCUG4310 was overproduced in
Escherichia coli
by means of a T7 promoter-based expression system. The overproducing system, scaled up in a 15-liter fermentor, yielded approximately 10 mg of BlaB protein per liter, mostly released in the culture supernatant. The enzyme was purified by two ion-exchange chromatographic steps with an overall yield of 66%. Analysis of the kinetic parameters revealed efficient activities (
k
cat
/

K
m

ratios of >10
6
M
−1
s
−1
) toward most penam and carbapenem compounds, with the exception of the 6-α-methoxypenam derivative temocillin and of biapenem, which were poorer substrates. Hydrolysis of cephalosporins was overall less efficient, with a remarkable variability that was largely due to variable affinities of the BlaB enzyme for different compounds. BlaB was also able to hydrolyze serine-β-lactamase inhibitors, including β-iodopenicillanate, sulbactam and, although less efficiently, tazobactam.
A Methylotrophic Pathway Participates in Pectin Utilization by
Candida boidinii
Authors: Nakagawa Tomoyuki , Miyaji Tatsuro , Yurimoto Hiroya , Sakai Yasuyoshi , Kato Nobuo , Tomizuka Noboru
Published: July 2002

The methylotrophic yeast
Candida boidinii
S2 was found to be able to grow on pectin or polygalacturonate as a carbon source. When cells were grown on 1% (wt/vol) pectin,
C. boidinii
exhibited induced levels of the pectin-depolymerizing enzymes pectin methylesterase (208 mU/mg of protein), pectin lyase (673 mU/mg), pectate lyase (673 mU/mg), and polygalacturonase (3.45 U/mg) and two methanol-metabolizing peroxisomal enzymes, alcohol oxidase (0.26 U/mg) and dihydroxyacetone synthase (94 mU/mg). The numbers of peroxisomes also increased ca. two- to threefold in cells grown on these pectic compounds (3.34 and 2.76 peroxisomes/cell for cells grown on pectin and polygalacturonate, respectively) compared to the numbers in cells grown on glucose (1.29 peroxisomes/cell). The cell density obtained with pectin increased as the degree of methyl esterification of pectic compounds increased, and it decreased in strains from which genes encoding alcohol oxidase and dihydroxyacetone synthase were deleted and in a peroxisome assembly mutant. Our study showed that methanol metabolism and peroxisome assembly play important roles in the degradation of pectin, especially in the utilization of its methyl ester moieties.
Degradation of Triphenyltin by a Fluorescent Pseudomonad
Authors: Inoue Hiroyuki , Takimura Osamu , Fuse Hiroyuki , Murakami Katsuji , Kamimura Kazuo , Yamaoka Yukiho
Published: July 2002

Triphenyltin (TPT)-degrading bacteria were screened by a simple technique using a post-column high-performance liquid chromatography using 3,3′,4′,7-tetrahydroxyflavone as a post-column reagent for determination of TPT and its metabolite, diphenyltin (DPT). An isolated strain, strain CNR15, was identified as
Pseudomonas chlororaphis
on the basis of its morphological and biochemical features. The incubation of strain CNR15 in a medium containing glycerol, succinate, and 130 μM TPT resulted in the rapid degradation of TPT and the accumulation of approximately 40 μM DPT as the only metabolite after 48 h. The culture supernatants of strain CNR15, grown with or without TPT, exhibited a TPT degradation activity, whereas the resting cells were not capable of degrading TPT. TPT was stoichiometrically degraded to DPT by the solid-phase extract of the culture supernatant, and benzene was detected as another degradation product. We found that the TPT degradation was catalyzed by low-molecular-mass substances (approximately 1,000 Da) in the extract, termed the TPT-degrading factor. The other fluorescent pseudomonads,
P. chlororaphis
ATCC 9446,
Pseudomonas fluorescens
ATCC 13525, and
Pseudomonas aeruginosa
ATCC 15692, also showed TPT degradation activity similar to strain CNR15 in the solid-phase extracts of their culture supernatants. These results suggest that the extracellular low-molecular-mass substance that is universally produced by the fluorescent pseudomonad could function as a potent catalyst to cometabolite TPT in the environment.
Mannose Phosphate Isomerase Isoenzymes in
Plutella xylostella
Support Common Genetic Bases of Resistance to
Bacillus thuringiensis
Toxins in Lepidopteran Species
Authors: Herrero Salvador , Ferré Juan , Escriche Baltasar
Published: July 2002

A strong correlation between two mannose phosphate isomerase (MPI) isoenzymes and resistance to Cry1A toxins from
Bacillus thuringiensis
has been found in a
Plutella xylostella
population. MPI linkage to Cry1A resistance had previously been reported for a
Heliothis virescens
population. The fact that the two populations share similar biochemical, genetic, and cross-resistance profiles of resistance suggests the occurrence of homologous resistance loci in both species.
Oligophilic Bacteria as Tools To Monitor Aseptic Pharmaceutical Production Units
Authors: Nagarkar Parag P. , Ravetkar Satish D. , Watve Milind G.
Published: July 2002

The bacterial loads of air, surfaces, and personnel in clean rooms are routinely monitored using a set of standard media. Bacteria that can grow on these media are a tiny fraction of the total numbers in any environment. A substantial proportion of bacteria long thought to be unculturable were recently shown to be oligophilic. Oligophile counts in clean rooms in our studies exceeded the standard plate counts by up to 2 orders of magnitude. They responded to disinfection routines in ways similar to the responses of conventional bacteria. We suggest that oligophiles are better tools than conventional bacteria for environmental monitoring in aseptic pharmaceutical production units.
The
cel4
Gene of
Agaricus bisporus
Encodes a β-Mannanase
Authors: Tang C. M. , Waterman L. D. , Smith M. H. , Thurston C. F.
Published: July 2002

Mannases have industrial uses in food and pulp industries, and their regulation may influence development of the mushrooms of commercially important basidiomycetes. We expressed an
Agaricus bisporus cel4
cDNA, which encodes a mannanase, in
Saccharomyces cerevisiae
and
Pichia pastoris
. CEL4 had no detectable activity on cellulose or xylan. This gene is the first isolated from this economically important fungus to encode a mannanase.
P. pastoris
secreted about three times more CEL4 than
S. cerevisiae
. The removal of the cellulose-binding domain of CEL4 lowered the secreted specific activity by
P. pastoris
by approximately 97%. The genomic sequence of
cel4
was isolated by screening a cosmid library of
A. bisporus
C54-
carb8
. The open reading frame was interrupted by 12 introns. The level of extracellular CEL4 increases dramatically at the postharvest stage in compost extracts of
A. bisporus
fruiting cultures. In laboratory liquid cultures of
A. bisporus
, the activity of CEL4 detected in the culture filtrate reached a maximum after 21 days. The levels of CEL4 broadly mirrored the levels of enzyme activity. In the Solka floc-bound mycelium, CEL4 protein showed a maximum after 2 to 3 weeks of culture and then declined. Changes in CEL4 activity during fruiting-body development suggest that hemicellulose utilization plays an important role in sporophore formation. The availability of the cloned gene will further studies of compost decomposition and the extracellular enzymes that fungi deploy in this process.
Membrane Permeabilization in Relation to Inactivation Kinetics of
Lactobacillus
Species due to Pulsed Electric Fields
Authors: Wouters Patrick C. , Bos Ad P. , Ueckert Joerg
Published: July 2002

Membrane permeabilization due to pulsed electric field (PEF) treatment of gram-positive
Lactobacillus
cells was investigated by using propidium iodide uptake and single-cell analysis with flow cytometry. Electric field strength, energy input, treatment time, and growth phase affected membrane permeabilization of
Lactobacillus plantarum
during PEF treatment. A correlation between PEF inactivation and membrane permeabilization of
L. plantarum
cells was demonstrated, whereas no relationship was observed between membrane permeabilization and heat inactivation. The same results were obtained with a
Lactobacillus fermentum
strain, but the latter organism was more PEF resistant and exhibited less membrane permeabilization, indicating that various bacteria have different responses to PEF treatment. While membrane permeabilization was the main factor involved in the mechanism of inactivation, the growth phase and the acidity of the environment also influenced inactivation. By using flow cytometry it was possible to sort cells in the
L. plantarum
population based on different cell sizes and shapes, and the results were confirmed by image analysis. An apparent effect of morphology on membrane permeabilization was observed, and larger cells were more easily permeabilized than smaller cells. In conclusion, our results indicate that the ability of PEF treatment to cause membrane permeabilization is an important factor in determining inactivation. This finding should have an effect on the final choice of the processing parameters used so that all microorganisms can be inactivated and, consequently, on the use of PEF treatment as an alternative method for preserving food products.
Novel Ring Cleavage Products in the Biotransformation of Biphenyl by the Yeast
Trichosporon mucoides
Authors: Sietmann Rabea , Hammer Elke , Specht Michael , Cerniglia Carl E. , Schauer Frieder
Published: July 2002

The yeast
Trichosporon mucoides
, grown on either glucose or phenol, was able to transform biphenyl into a variety of mono-, di-, and trihydroxylated derivatives hydroxylated on one or both aromatic rings. While some of these products accumulated in the supernatant as dead end products, the
ortho
-substituted dihydroxylated biphenyls were substrates for further oxidation and ring fission. These ring fission products were identified by high-performance liquid chromatography, gas chromatography-mass spectrometry, and nuclear magnetic resonance analyses as phenyl derivatives of hydroxymuconic acids and the corresponding pyrones. Seven novel products out of eight resulted from the oxidation and ring fission of 3,4-dihydroxybiphenyl. Using this compound as a substrate, 2-hydroxy-4-phenylmuconic acid, (5-oxo-3-phenyl-2,5-dihydrofuran-2-yl)acetic acid, and 3-phenyl-2-pyrone-6-carboxylic acid were identified. Ring cleavage of 3,4,4′-trihydroxybiphenyl resulted in the formation of [5-oxo-3-(4′-hydroxyphenyl)-2,5-dihydrofuran-2-yl]acetic acid, 4-(4′-hydroxyphenyl)-2-pyrone-6-carboxylic acid, and 3-(4′-hydroxyphenyl)-2-pyrone-6-carboxylic acid. 2,3,4-Trihydroxybiphenyl was oxidized to 2-hydroxy-5-phenylmuconic acid, and 4-phenyl-2-pyrone-6-carboxylic acid was the transformation product of 3,4,5-trihydroxybiphenyl. All these ring fission products were considerably less toxic than the hydroxylated derivatives.
Chlorine Disinfection of Atypical Mycobacteria Isolated from a Water Distribution System
Authors: Le Dantec Corinne , Duguet Jean-Pierre , Montiel Antoine , Dumoutier Nadine , Dubrou Sylvie , Vincent Véronique
Published: July 2002

We studied the resistance of various mycobacteria isolated from a water distribution system to chlorine. Chlorine disinfection efficiency is expressed as the coefficient of lethality (liters per minute per milligram) as follows:
Mycobacterium fortuitum
(0.02) >
M. chelonae
(0.03) >
M. gordonae
(0.09) >
M. aurum
(0.19). For a
C
 · 
t
value (product of the disinfectant concentration and contact time) of 60 mg · min · liter
−1
, frequently used in water treatment lines, chlorine disinfection inactivates over 4 log units of
M. gordonae
and 1.5 log units of
M. fortuitum
or
M. chelonae
.
C
 · 
t
values determined under similar conditions show that even the most susceptible species,
M. aurum
and
M. gordonae
, are 100 and 330 times more resistant to chlorine than
Escherichia coli
. We also investigated the effects of different parameters (medium, pH, and temperature) on chlorine disinfection in a chlorine-resistant
M. gordonae
model. Our experimental results follow the Arrhenius equation, allowing the inactivation rate to be predicted at different temperatures. Our results show that
M. gordonae
is more resistant to chlorine in low-nutrient media, such as those encountered in water, and that an increase in temperature (from 4°C to 25°C) and a decrease in pH result in better inactivation.
Norwalk-Like Virus Sequences in Mineral Waters: One-Year Monitoring of Three Brands
Authors: Beuret Christian , Kohler Dorothe , Baumgartner Andreas , Lüthi Thomas M.
Published: July 2002

In a recent study, RNA with nucleotide sequeces specific for “Norwalk-like viruses” (NLV) was detected in 11 different brands of European mineral waters. To clarify this finding, a 1-year monitoring study was conducted. Samples of three European brands of mineral water without gas were monitored weekly by reverse transcriptase PCR using generic and genogroup-specific oligonucleotides. Additional analyses were performed to investigate a possible correlation between NLV sequence contamination and mineral water lot numbers, the long-term stability (persistence) of NLV sequences in mineral water, and the level of contamination. NLV sequences were detected in 53 of 159 samples analyzed (33%) and belonged entirely to genogroup II. Although all NLV strains identified were closely related, three mineral water brand-specific clusters could be identified for both primer systems by sequencing. Analyses of second samples from lots previously shown to be positive for NLV sequences gave corresponding results in 45 of 53 cases (85%) (within a six-pack). NLV persistence was tested by analyzing 10 positive samples after 6 and 12 months of storage in darkness at room temperature. After 6 months, all samples remained positive; after 12 months, 9 of 10 samples were still positive for NLV sequences. No NLV sequences could be detected by analysis of 0.1-liter aliquots of 53 samples shown to be positive by testing of 1-liter volumes. Based on this fact and a test sensitivity of approximately 10 viral units, levels of contamination in positive mineral water samples were estimated to be in the range of 10 to 100 genomic equivalents per liter.
Impaired Cutinase Secretion in
Saccharomyces cerevisiae
Induces Irregular Endoplasmic Reticulum (ER) Membrane Proliferation, Oxidative Stress, and ER-Associated Degradation
Authors: Sagt C. M. J. , Müller W. H. , van der Heide L. , Boonstra J. , Verkleij A. J. , Verrips C. T.
Published: July 2002

Impaired secretion of the hydrophobic CY028 cutinase invokes an unfolded protein response (UPR) in
Saccharomyces cerevisiae
cells. Here we show that the UPR in CY028-expressing
S. cerevisiae
cells is manifested as an aberrant morphology of the endoplasmic reticulum (ER) and as extensive membrane proliferation compared to the ER morphology and membrane proliferation of wild-type CY000-producing
S. cerevisiae
cells. In addition, we observed oxidative stress, which resulted in a 21-fold increase in carbonylated proteins in the CY028-producing
S. cerevisiae
cells. Moreover, CY028-producing
S. cerevisiae
cells use proteasomal degradation to reduce the amount of accumulated CY028 cutinase, thereby attenuating the stress invoked by CY028 cutinase expression. This proteasomal degradation occurs within minutes and is characteristic of ER-associated degradation (ERAD). Our results clearly show that impaired secretion of the heterologous, hydrophobic CY028 cutinase in
S. cerevisiae
cells leads to protein aggregation in the ER, aberrant ER morphology and proliferation, and oxidative stress, as well as a UPR and ERAD.