bluuebunny/crossref_metadata_2025 huggingface dataset:
Individual differences in factors that modulate storage and
retrieval of traumatic memories
Authors: HOWE MARK L.
Published: July 2002

It is argued that memory for traumatic events is similar to that for
other distinctive, personally significant events regardless of whether they are affectively positive
or negative. Examined in this light, the focus now shifts to the role of individual differences in
neurobiological, social, cognitive, and constitutional factors that conspire to determine long-term
retention of significant autobiographical experiences. What is known about these factors in
determining memorability is reviewed, issues of measurement inadequacies discussed, and
recommendations for further research outlined.
Dysphagia following stroke
Authors: Smithard David G
Published: July 2002

Unfortunately, stroke is an extremely common disease. Around 100 000 people suffer a first-ever stroke each year. Stroke is the third commonest cause of death in the western world and is a major cause of long-term disability. Many patients admitted acutely to hospital after stroke will have a transient or persistent problem with their swallowing. Impaired swallowing results in a failure to maintain nutritional status and hydration, a break-down of vital organs, increasing susceptibility to infection and an increased likelihood of dying.
NOTES RELATING TO THE FLORA OF BHUTAN: XLI. COMPOSITAE(ASTERACEAE)
Authors: GRIERSON A. J. C. , SPRINGATE L. S.
Published: July 2002

The following new species, subspecies and combinations are proposed for plants occurring in the Flora of Bhutan area: Anaphalis cooperi Grierson & Springate, Artemisia bhutanica Grierson & Springate, Ixeridium beauverdianum (H.Lév.) Springate, Ligularia lancifera (J.R.Drumm.) Grierson, L. latiligulata (R.D.Good) Springate, Parasenecio chenopodifolius (DC.) Grierson, Saussurea donkiah C.B.Clarke ex Springate, S. pinnatiphylla Grierson & Springate, Tanacetum tatsienense var. tanacetopsis (W.W.Sm.) Grierson and Youngia silhetensis subsp. bhutanica Grierson & Springate. A description of Ligularia latiligulata is provided. A lectotype is designated for Saussurea obscura Lipsch.
Feminine Beauty, National Identity and Political Conflict in Postwar Italy, 1945–1954
Authors: Gundle Stephen
Published: July 2002

After 1945 the Italian tradition of feminine beauty was redefined in a democratic context in which women, for the first time, became full citizens. Faced with a far-reaching challenge from Hollywood, traditional criteria of beauty were first strenuously defended and then modified and commercialised. Beauty contests proved to be a vital vehicle in this transition, since they acted both as a forum for the reassertion of Italian beauty and as a vehicle for the displacement of old ideas centred on the face with a new concept based on the eroticised body. This transition became bound up with the ongoing political conflict between Catholics and the left for the moral and political leadership of the country. While both, with different emphases, championed ‘natural’ at the expense of American-style ‘manufactured’ beauty, competition led them to engage with, and in some way adopt, the sexualised beauty that was the hallmark of the role of the United States in furnishing new models for the consumer society that would develop rapidly in the later 1950s.
The blitz, civilian morale and the city: mass-observation and working-class culture in Britain, 1940–41
Authors: Beaven Brad , Griffiths John
Published: July 2002

One of the most difficult concepts in both contemporary and academic accounts of the Second World War is that of civilian morale. This paper uses evidence from the Mass-Observation Archive to argue that understanding fluctuations in morale can only be understood through an exploration of working-class culture during the 1930s and 1940s. The paper examines difficulties of defining ‘morale’ and goes on to argue that the pattern of bombing in urban centres and the continuity of working-class institutions helped shape and maintain morale during the critical period of 1940–41
A script-based AAC system for transactional interaction
Authors: DYE RICHARD , ALM NORMAN , ARNOTT JOHN L. , HARPER GILLIAN , MORRISON ARTHUR I.
Published: July 2002

Non-speaking people often rely on AAC (Augmentative and Alternative
Communication)
devices to assist them to communicate. These AAC devices are slow to operate,
however, and
as a result conversations can be very difficult and frequently break down.
This is especially
the case when the conversation partner is unfamiliar with this method of
communication, and
is a big obstacle to many people when they wish to conduct simple everyday
transactions. A
way of improving the performance of AAC devices by using scripts is discussed.
A prototype
system to test this idea was constructed, and a preliminary experiment
performed with
promising results. A practical AAC device which incorporates scripts was
then developed,
and is described.
Spectral modelling and timbre hybridisation programs for computer music
Authors: BEAUCHAMP JAMES , HORNER ANDREW
Published: July 2002

Software packages developed for visualising time-varying timbres, finding parameter settings for modelling acoustic instrument tones, and for synthesising timbres are described. The sndan package, written in C for Unix machines, provides spectrum analysis, pitch tracking, spectrum display, parameter modification, and additive synthesis. Other programs that estimate the best possible parameters for recreating acoustic sounds using techniques such as multiple FM and wavetable synthesis and extended nonlinear/filter synthesis are outlined. Hybrid instruments created by fashioning sounds out of the recombined spectral characteristics of two or more very different tones are also presented.
The set1Δ mutation unveils a novel signaling pathway relayed by the Rad53-dependent hyperphosphorylation of replication protein A that leads to transcriptional activation of repair genes
Authors: Schramke Vera , Neecke Holger , Brevet Vanessa , Corda Yves , Lucchini Giovanna , Longhese Maria Pia , Gilson Eric , Géli Vincent
Published: July 2002

SET domain proteins are present in chromosomal proteins involved in epigenetic control of transcription. The yeast SET domain protein Set1p regulates chromatin structure, DNA repair, and telomeric functions. We investigated the mechanism by which the absence of Set1p increases DNA repair capacities of checkpoint mutants. We show that deletion ofSET1 induces a response relayed by the signaling kinase Rad53p that leads to the MEC1/TEL1-independent hyperphosphorylation of replication protein A middle subunit (Rfa2p). Consequently, the binding of Rfa2p to upstream repressing sequences (URS) of repair genes is decreased, thereby leading to their derepression. Our results correlate the set1Δ-dependent phosphorylation of Rfa2p with the transcriptional induction of repair genes. Moreover, we show that the deletion of the amino-terminal region of Rfa2p suppresses the sensitivity to ultraviolet radiation of amec3Δ checkpoint mutant, abolishes the URS-mediated repression, and increases the expression of repair genes. This work provides an additional link for the role of Rfa2p in the regulation of the repair capacity of the cell and reveals a role for the phosphorylation of Rfa2p and unveils unsuspected connections between chromatin, signaling pathways, telomeres, and DNA repair.
Antisense Expression of the Peptide Transport Gene AtPTR2-B Delays Flowering and Arrests Seed Development in Transgenic Arabidopsis Plants
Authors: Song W. , Koh S. , Czako M. , Marton L. , Drenkard E. , Becker J. M. , Stacey G.
Published: July 2002

Previously, we identified a peptide transport gene, AtPTR2-B, from Arabidopsis thaliana that was constitutively expressed in all plant organs, suggesting an important physiological role in plant growth and development. To evaluate the function of this transporter, transgenic Arabidopsis plants were constructed expressing antisense or sense AtPTR2-B. Genomic Southern analysis indicated that four independent antisense and three independent sense AtPTR2-B transgenic lines were obtained, which was confirmed by analysis of the segregation of the kanamycin resistance gene carried on the T-DNA. RNA blot data showed that the endogenous AtPTR2-B mRNA levels were significantly reduced in transgenic leaves and flowers, but not in transgenic roots. Consistent with this reduction in endogenous AtPTR2-B mRNA levels, all four antisense lines and one sense line exhibited significant phenotypic changes, including late flowering and arrested seed development. These phenotypic changes could be explained by a defect in nitrogen nutrition due to the reduced peptide transport activity conferred by AtPTR2-B. These results suggest that AtPTR2-B may play a general role in plant nutrition. The AtPTR2-B gene was mapped to chromosome 2, which is closely linked to the restriction fragment length polymorphism marker m246.
Identification of a Novel Isoform of the Chloroplast-Coupling Factor α-Subunit 1
Authors: Burkey Kent O. , Mathis James N.
Published: July 2002

Studies were conducted to identify a 64-kD thylakoid membrane protein of unknown function. The protein was extracted from chloroplast thylakoids under low ionic strength conditions and purified to homogeneity by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Four peptides generated from the proteolytic cleavage of the wheat 64-kD protein were sequenced and found to be identical to internal sequences of the chloroplast-coupling factor (CF1) α-subunit. Antibodies for the 64-kD protein also recognized the α-subunit of CF1. Both the 64-kD protein and the 61-kD CF1α-subunit were present in the monocots barley (Hordeum vulgare), maize (Zea mays), oat (Avena sativa), and wheat (Triticum aestivum); but the dicots pea (Pisum sativum), soybean (Glycinemax Merr.), and spinach (Spinacia oleracea) contained only a single polypeptide corresponding to the CF1 α-subunit. The 64-kD protein accumulated in response to high irradiance (1000 μmol photons m−2 s−1) and declined in response to low irradiance (80 μmol photons m−2 s−1) treatments. Thus, the 64-kD protein was identified as an irradiance-dependent isoform of the CF1 α-subunit found only in monocots. Analysis of purified CF1 complexes showed that the 64-kD protein represented up to 15% of the total CF1 α-subunit.
Purification and cDNA Cloning of Maize Poly(ADP)-Ribose Polymerase
Authors: Mahajan Pramod B. , Zuo Zhuang
Published: July 2002

Poly(ADP)-ribose polymerase (PADPRP) has been purified to apparent homogeneity from suspension cultures of the maize (Zea mays) callus line. The purified enzyme is a single polypeptide of approximately 115 kD, which appears to dimerize through an S-S linkage. The catalytic properties of the maize enzyme are very similar to those of its animal counterpart. The amino acid sequences of three tryptic peptides were obtained by microsequencing. Antibodies raised against peptides from maize PADPRP cross-reacted specifically with the maize enzyme but not with the enzyme from human cells, and vice versa. We have also characterized a 3.45-kb expressed-sequence-tag clone that contains a full-length cDNA for maize PADPRP. An open reading frame of 2943 bp within this clone encodes a protein of 980 amino acids. The deduced amino acid sequence of the maize PADPRP shows 40% to 42% identity and about 50% similarity to the known vertebrate PADPRP sequences. All important features of the modular structure of the PADPRP molecule, such as two zinc fingers, a putative nuclear localization signal, the automodification domain, and the NAD+-binding domain, are conserved in the maize enzyme. Northern-blot analysis indicated that the cDNA probe hybridizes to a message of about 4 kb.
The use of statistical process control in food packing
Authors: Grigg Nigel P. , Walls Lesley
Published: July 2002

Presents a synthesis of the early findings from an ongoing project researching the issues surrounding the use of SPC in a food packing environment. A cognitive mapping approach has been utilised to make sense of the complex and varied data resulting from the survey, case studies and interviews carried out to date. This methodological approach is described, and its application illustrated in relation to the research topic. Argues that SPC is one weapon in an arsenal of quality management techniques that food companies can use to consolidate or improve their position in an increasingly competitive marketplace. Once successfully adopted SPC can offer proven operational and financial benefits, but the ability of the organisation to successfully achieve implementation will depend upon a number of organisational factors. Finally, presents the agenda for further research which outlines how this ongoing project is intended to be taken forward from this point.
Personal competencies, organizational competencies, and employability
Authors: Civelli Franco
Published: July 2002

In recent years, it has become more and more important to recognize people’s characteristics which are no longer “immutable”. Hence the path followed with competences, the approach in the organizational world called “the competence based approach”. “Employability” highlights a critical point emerging right at the time when the deterministic and mechanistic approach, typical of the traditional job market’s “demand‐offer” relationship must give way to better differentiated approaches, in which symbolic, cultural, social and value variables are becoming fundamental. The issue of competences, which, with different approaches, has emerged in the organizational world, can be easily related to the problem of employability. It is becoming more and more urgent to be able to identify the ownership of specific competences and their implementation, at a given time. New professionalism makes it necessary for people and organizations to understand what kind of “behavioural language” will have an effective impact on fast changing situations and scenarios.
Design effects of retail floor space in Hong Kong
Authors: Baldwin Graeme
Published: July 2002

This paper considers the effects of the shape of supermarket retail floor space on patronage turnover in Hong Kong. From a sample of stores it was observed that many possessed unique and irregular shapes, and some traded on more than one floor level. It was determined that the factors of complexity of shape and the dual‐floor trading concept had no effect on the patronage turnover. The conclusion drawn is that the most likely reasons for these results rest with customer familiarity and tolerance, allied to small shopping loads. Details of the criteria for store selection for inclusion in the survey are given. Data collected were subjected to statistical testing to determine the extent of correlation.
Alkyd emulsion paints: properties, challenges and solutions
Authors: Beetsma Jochum
Published: July 2002

Some of the properties of paints based on alkyd emulsion are discussed and they are divided into four categories. Colloidal stability of water based paints is predominantly governed by osmotic and electrostatic repulsion of both the binder and the pigment particles. The rheological behaviour of paints based on binder dispersions should be optimised by using thickeners with the proper mix of hydrophilic and hydrophobic polymeric segments. Stability of drying properties of alkyd emulsion paints upon storage can be strongly improved by preventing the use of ketoximes as anti‐skinning agents and by selecting the proper driers. Properties of the dried paints depend strongly on the process of film formation. The protective and aesthetical quality of films based on binder dispersions is governed by the key parameters of the resin that is within the droplets; viscosity, miscibility and the ability of the binder to undergo crosslinking. To obtain the total package of desired properties of water based paints it is necessary that all of the paint components are adjusted to each other. This can only be done if the companies that develop and market the raw materials work closely together. The use of fundamental knowledge in such co‐makerships results in better and faster developments.
An analytical scheme for the change of the apparel design process towards quick response
Authors: Forza Cipriano , Vinelli Andrea
Published: July 2002

Proposes models of a descriptive and interpretative type which examine the temporal sequences of the activities and decisions taken in the textile apparel chain with reference to design. Examines the opportunities for improvement and also identifies the obstacles that interfere with the realization of quick response (QR) in design. Analyses, using the proposed models, the possible interventions along the chain as regards design activities and interaction between these and the production and sales activities. Highlights the following: the reduction of design lead time, through the parallelization of fabric and garment design and through the use of information technology; the reduction of the variety of production input without penalizing the variety perceived by the final consumer; and the acquisition, during design, of preliminary information on future sales, in order to rationalize the offer and carry out the initial assortment of production input.
Identification of related proteins with weak sequence identity using secondary structure information
Authors: Geourjon Christophe , Combet Christophe , Blanchet Christophe , Deléage Gilbert
Published: July 2002

Molecular modeling of proteins is confronted with the problem of finding homologous proteins, especially when few identities remain after the process of molecular evolution. Using even the most recent methods based on sequence identity detection, structural relationships are still difficult to establish with high reliability. As protein structures are more conserved than sequences, we investigated the possibility of using protein secondary structure comparison (observed or predicted structures) to discriminate between related and unrelated proteins sequences in the range of 10%–30% sequence identity. Pairwise comparison of secondary structures have been measured using the structural overlap (Sov) parameter. In this article, we show that if the secondary structures likeness is >50%, most of the pairs are structurally related. Taking into account the secondary structures of proteins that have been detected by BLAST, FASTA, or SSEARCH in the noisy region (with high E value), we show that distantly related protein sequences (even with <20% identity) can be still identified. This strategy can be used to identify three‐dimensional templates in homology modeling by finding unexpected related proteins and to select proteins for experimental investigation in a structural genomic approach, as well as for genome annotation.
Conformational changes in chemically modified Escherichia coli thioredoxin monitored by H/D exchange and electrospray ionization mass spectrometry
Authors: Kim Moo‐Young , Maier Claudia S. , Reed Donald J. , Deinzer Max L.
Published: July 2002

Hydrogen/deuterium (H/D) exchange in combination with electrospray ionization mass spectrometry and near‐ultraviolet (UV) circular dichroism (CD) was used to study the conformational properties and thermal unfolding of Escherichia coli thioredoxin and its Cys32‐alkylated derivatives in 1% acetic acid (pH 2.7). Thermal unfolding of oxidized (Oxi) and reduced (Red) ‐thioredoxin (TRX) and Cys‐32‐ethylglutathionyl (GS‐ethyl‐TRX) and Cys‐32‐ethylcysteinyl (Cys‐ethyl‐TRX), which are derivatives of Red‐TRX, follow apparent EX1 kinetics as charge‐state envelopes, H/D mass spectral exchange profiles, and near‐UV CD appear to support a two‐state folding/unfolding model. Minor mass peaks in the H/D exchange profiles and nonsuperimposable MS‐ and CD‐derived melting curves, however, suggest the participation of unfolding intermediates leading to the conclusion that the two‐state model is an oversimplification of the process. The relative stabilities as measured by melting temperatures by both CD and mass spectral charge states are, Oxi‐TRX, GS‐ethyl‐TRX, Cys‐ethyl‐TRX, and Red‐TRX. The introduction of the Cys‐32‐ethylglutathionyl group provides extra stabilization that results from additional hydrogen bonding interactions between the ethylglutathionyl group and the protein. Near‐UV CD data show that the local environment near the active site is perturbed to almost an identical degree regardless of whether alkylation at Cys‐32 is by the ethylglutathionyl group, or the smaller, nonhydrogen‐bonding ethylcysteinyl group. Mass spectral data, however, indicate a tighter structure for GS‐ethyl‐TRX.
A Model of Crack Nucleation in Layered Electronic Assemblies Under Thermal Cycling
Authors: Chandra A. , Huang Y. , Jiang Z. Q. , Hu K. X. , Fu G.
Published: July 2002

A model for crack nucleation in layered electronic assemblies under thermal cycling is developed in this paper. The present model includes three scales: (i) at the microscale or the mechanism level, the damage mechanisms such as diffusive void growth or fatigue cracks, determine the damage growth rate; (2) at an intermediate mesoscale, the localized damage bands are modeled as variable stiffness springs connecting undamaged materials; and (iii) at the macroscale or the continuum level, the localized damage band growing in an otherwise undamaged material is modeled as an array of dislocations. The three scales are then combined together to incorporate damage mechanisms into continuum analysis. Traditional fracture mechanics provides a crack propagation model based on pre-existing cracks. The present work provides an approach for predicting crack nucleation. The proposed model is then utilized to investigate crack nucleations in three-layered electronic assemblies under thermal cycling. The damage is observed to accumulate rapidly in the weakest regions of the band. Estimates are obtained for critical time or critical number of cycles at which a macroscopic crack will nucleate in these assemblies under thermal cycling. This critical number of cycles is found to be insensitive to the size of the damage cluster, but decreases rapidly as the local excess damage increases. [S1043-7398(00)00503-X]
Transport in Stochastic Fibrous Networks
Authors: Cheng X. , Sastry A. M. , Layton B. E.
Published: July 2002

Some fundamental issues concerning the design and performance of stochastic porous structures are examined, stemming from application of advanced fibrous electrode substrates in NiMH automotive cells. These electrodes must resist corrosion and local failures under hundreds of charge/discharge cycles. Such fibrous materials can be effectively used as substrates for chemical reactions because of their combinations of high surface area and high conductivity. Key questions concerning the relationships among connectivity and conductivity, scale and variability in material response are addressed. Two techniques are developed and compared for use in predicting these materials’ conductivity. The first approach uses a statistical technique in conjunction with an adaptation of classic micromechanical models. The second approach uses the statistical generation technique, followed by an exact calculation of 2D network conductivity. The two techniques are compared with one another and with classic results. Several important conclusions about the design of these materials are presented, including the importance of use of fibers with aspect ratios greater than at least 50, the weak effect of moderate alignment for unidirectional conductivity, and the weak power-law behavior of conductivity versus volume fraction over the range of possible behaviors.
Close-Contact Melting Inside an Elliptical Cylinder
Authors: Fomin Sergei A. , Wilchinsky Alexander V. , Saitoh Takeo S.
Published: July 2002

An approximate mathematical model of contact melting in a horizontal elliptic cylinder is developed. The main characteristic scales and nondimensional parameters that describe the principal features of the melting process are found. It is shown that melting rate depends on the shape of the capsule. This is especially important for the design of practical latent heat thermal energy systems. [S0199-6231(00)00504-9]
Constitutive Data for Powder Compaction Modeling
Authors: Sinka I. C. , Cocks A. C. F. , Tweed J. H.
Published: July 2002

The compaction behavior of steel powders, hard metals, and ceramic powders have been investigated using a newly developed high pressure triaxial testing facility. Results from isostatic compaction, simulated closed die compaction, and compaction along different radial loading paths in stress space are presented for six commercial powders. The experimental data are compared and considerations regarding the constitutive modeling of the compaction response of the different classes of materials are presented.
Generalization of νt-92 Turbulence Model for Shear-Free and Stagnation Point Flows
Authors: Secundov A. N. , Strelets M. Kh. , Travin A. K.
Published: July 2002

The one-equation, eddy-viscosity transport model of Gulyaev, Kozlov, and Secundov, νt-92, is modified and supplemented by an equation for the turbulence length scale. The advantages of the model developed here are demonstrated by computing a shear-free “boundary layer” on a flat plate, and the flow and heat transfer near the forward stagnation line of a circular cylinder. Both cases are known to be challenging for conventional turbulence models.
Constitutive Relations for Inelastic Deformation and Damage Accumulation in Hard Alpha Titanium
Authors: Chan Kwai S.
Published: July 2002

The constitutive properties of hard alpha Ti were recently generated by Chan et al., 2000, “Constitutive Properties of Hard Alpha Titanium,” Metall. and Maters. Trans. A, Vol. 31A, pp. 3029–3040, using uniaxial compression, indirect tension, indentation, and plane strain compression tests. Flow stress and fracture strength of hard alpha were measured as a function of stress state, strain rate, temperature, and nitrogen content. Hard alpha exhibited plastic flow at low nitrogen contents (<4 wt. percent N), but elastic fracture at high nitrogen contents (>6 wt. percent N). In this paper, this set of constitutive data is used to develop constitutive equations for describing the inelastic deformation and damage accumulation behavior of hard alpha Ti.
Quantifying Fuel/Air Unmixedness in Premixing Nozzles Using an Acetone Fluorescence Technique
Authors: Stufflebeam J. H. , Kendrick D. W. , Sowa W. A. , Snyder T. S.
Published: July 2002

The ability of a lean-premixed combustion system to minimize emissions while maintaining combustion stability over the operating curve relies upon how well the fuel nozzle premixes the fuel and air. As the level of premixing increases, NOx emissions at a given flame temperature decrease until a perfectly premixed condition is achieved. The objective of this paper is to quantify the level of premixing achieved by a premixing nozzle using an acetone fluorescence technique and determine its relationship to NOx emissions and combustion stability. The technique of using acetone fluorescence has been used as a fast and quantitative diagnostic to map the fuel-air distribution. This technique has been applied to the development of a lean premixing nozzle to measure the fuel air distribution at the fuel nozzle exit plane. In this study, the fuel air distribution is presented as two-dimensional images. The average fuel/air ratio and the standard deviation are calculated at various annular regions to determine the distribution as a function of radius. A single unmixedness parameter (σ/μ) over the entire annulus is also calculated to allow relative ranking of the various fuel nozzle configurations. The fluorescence data is acquired for various nozzle hardware configurations in an atmospheric test facility. Fuel and air flow conditions are determined by scaling engine conditions to cold flow conditions and matching the fuel to air momentum ratio at the fuel injection site. Measured fuel/air distributions, six mm downstream of the nozzle exit plane, from the acetone fluorescence technique are correlated to emissions and acoustic measurements made at full pressure and temperature conditions in a single-nozzle test rig. The paper includes a description of the acetone fluorescence technique, the method for optimizing the fuel/air distribution through changes to the main gas fuel injection array, and correlations made between the fuel/air distribution, nozzle geometry, power setting, emissions, and combustor acoustics.
On-Line Thinning Measurement in the Deep Drawing Process
Authors: Berger Moshe , Zussman Eyal
Published: July 2002

The conventional deep drawing process is limited to a certain Limit Drawing Ratio (LDR), beyond which localized wall thinning and rupture occur. One way to increase the LDR is to try to capture the onset of necking and to adjust process parameters in order to delay or avoid necking. This paper describes a method for monitoring the wall thickness of a cup during the deep drawing process. Measurement utilizes a noncontact ultrasound gauge that is located orthogonally to the drawn cup’s wall and is immersed in oil to create an acoustic coupling. Monitoring is based upon a deep drawing process model using a thin blank with a round cross-section. Thickness distribution along a longitudinal axis is predicted and is used as a trajectory to track in-process thinning variations that may lead to tearing. The robustness of the measurement system is examined by applying the technique in different experiments. Results show that in-process measurements correlate well with grid strain analysis of a formed sheet metal part.
Uniaxial Stress Deformation Experiment for Validation of 3-D Dislocation Dynamics Simulations
Authors: Lassila David H. , LeBlanc Mary M. , Kay Gregory J.
Published: July 2002

An apparatus has been developed for performing compression deformation experiments on oriented metallic single crystals to provide data for validation of 3-D dislocation dynamics simulations. The experiment is performed under conditions that allow unconstrained motion of the upper and lower compression platen, and thus a relatively uniform state of axial stress is maintained during the deformation. Experiments have been performed on high-purity Mo single crystal and polycrystalline Cu. Various aspects of the experimental procedures and results are presented. Possible usages of the experimental data for the validation of 3-D dislocation dynamics simulations are discussed.
Poly(p-Phenylenevinylene) UPS Valence Band Spectra
Authors: Lögdlund M. , Salaneck W. R.
Published: July 2002

The research field of conjugated polymers is rapidly increasing due to their potential, and demonstrated, use as electroactive materials. In particular, in connection with the progress made in the fabrication of light emitting diodes (LEDs) from conjugated polymers, some of the most promising results have been obtained with poly(p-phenylenevinylene), or PPV, as the light emission medium [J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burn, and A. B. Holmes, Nature 347, 539 (1990); R. H. Friend, in Nobel Symposium in Chemistry: Conjugated Polymers and Related Materials; The Interconnection of Chemical and Electronic Structure, edited by W. R. Salaneck, I. Lundstrom, and B. Ranby (Oxford Science, Oxford, 1993)]. The electronic structure of these conjugated polymers gives important information towards a better understanding of the performance of the devices [D. A. dos Santos, C. Quattrocchi, R. H. Friend, and J. L. Bredas, J. Chem. Phys. 100, 3301 (1994)]. Here, ultraviolet photoelectron spectroscopy (UPS) valence band spectra of PPV are presented. Other valence band spectra of PPV can be found in the literature [M. J. Obrzut and F. E. Karasz, Macromolecules 22, 458 (1989); K. Seki, S. Asada, T. Mori, H. Inokuchi, I. Murase, T. Ohnishi, and T. Nogushi, Solid State Commun. 74, 677 (1990)]. The present spectra are, however, better resolved and agree very well with theoretical modeling [M. Lögdlung, W. R. Salaneck, F. Meyers, J. L. Bredas, G. A. Arbuckle, R. Friend, A. B. Holmes, and G. Froyer, Macromolecules 26, 3815 (1993)].
An Investigation of the Surface Chemistry of a Polyetherurethaneurea Biomaterial Using XPS
Authors: Porter Stephen C. , Ratner Buddy D.
Published: July 2002

A poly(tetramethylene oxide) [PTMO] based polyetherurethaneurea (PEUU), produced by Polymer Technology Group Inc. (Emeryville, CA) as a Primary Reference Material, was spin-cast from a 3% (w/v) DMAc solution onto a glass cover slip. The polymer coating was analyzed at ambient temperature by XPS using a 55° take-off angle. An elemental survey scan shows the presence of C, N, and O (no trace elements were detected). The C 1s spectrum shows a nearly equal concentration of ether and hydrocarbon environments, suggesting that surface localization of the PTMO soft segment is occuring. A broadened peak at higher binding energy (~289.1 eV) is indicative of the presence of both urea and urethane nitrogens. The N 1s peak location suggests that there is a greater contribution from urea groups. The dominant contributors to the O 1s spectra are ether functionalities. The urea and urethane contributions are apparent as high and low binding energy tails but are too small to be resolved accurately.
Plasma etch/deposition modeling: A new dynamically coupled multiscale code and comparison with experiment
Authors: Bear Michael J. , Guillory John U.
Published: July 2002

Next-generation plasma-process modeling tools can provide new insight into process dynamics by resolving the diverse length and time scales present in reactor systems. The length scales range from the size of the reactor (∼10 cm) to surface details (∼100 nm), and time scales from electron sheath-transit times (nanoseconds) to total process time (minutes). Other key features include dynamic coupling of the plasma and solid (particles and fields), and the ability to model realistic surface interactions (deposition, etch, sputter, polymerization, etc.). A computational tool has been developed which provides all of these features through the coupling of heterogeneous code modules [hybrid plasma, particle in cell (PIC) plasma and solid surface chemistry] and through time-sampling techniques. The hybrid code (particle ions, fluid electrons) provides the basis for modeling the large-scale plasma reactor using a finite-element mesh to represent complex reactor geometries. The PIC code is used in the dynamic sheath boundary region to account for electron movement. The solid surface chemistry code is specially developed to model complex interactions between surface mechanisms, such as the formation of polymer and its possible removal by high-energy particles. The solid surface module uses a finite element scheme with adaptive mesh refinement (on a many-cycle time scale) to follow the complex surface evolution. These code modules exchange information on a sub-rf-period timescale, allowing for direct solid/plasma interactions. The long process times (minutes) are simulated by result sampling and using the slow evolution of the plasma/solid system. The code also performs surface charge migration and local gas heating to more completely represent the physical processes occurring in a plasma processing operation. The modeling of plasma processing must also account for the multilayer films and many species of particles and material types. The incorporation of this information in the simulations has demonstrated mask erosion. The simulations performed using this code have also shown good correlation to experimental results for steady state etch rates, etch rates as a function of via size, sidewall polymer evolution, and the production of “sputter wind” and surface charging. In deposition mode, the simulations demonstrate the experimentally observed polymer and deposited film topology.
Plasma polymerized methylsilane I: Characterization of thin photosensitive films for advanced lithography applications
Authors: Monget C. , Joubert O. , Inglebert R. L.
Published: July 2002

Plasma polymerized methylsilane (PPMS) films are promising photosensitive layers for 248 and 193 nm lithography applications. These a-Si1−xCx:H films are deposited in a low power plasma of methylsilane gas using a commercial tool. The effect of substrate temperature, pressure in the chamber and rf power injected in the source on optical properties and chemical composition of the PPMS films have been studied using spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy. FTIR experiments show that the PPMS structure is organized around a Si:H network with intact methyl groups. The correlation between deposition parameters and PPMS films properties is discussed.
Review of Pressure Measurement Techniques for Ultrahigh Vacua
Authors: Lafferty J. M.
Published: July 2002

This review includes a brief listing of the physical principles used in pressure measuring devices and a detailed discussion of selected topics associated with ionization gauges. Ionization gauges are currently the only devices available for measuring pressures in the extreme ultrahigh vacuum region. This is not because of their high sensitivity, but rather because of development of techniques for measuring small currents conveniently. Twenty-five years ago, it was not possible to measure the lowest pressures attainable. Today the situation is reversed; the lowest total pressures currently produced not only can be measured, but the composition of the residual gases can be analyzed as well. Notwithstanding their great popularity, ionization gauges suffer from many sources of error. Despite these difficulties, some of which are discussed in this paper, the total pressure ionization gauge can, when properly designed and operated, give pressure readings that are accurate to better than an order of magnitude and perhaps even a few percent under ideal conditions when carefully calibrated and the gas composition is known. The low pressure limit of present ionization gauges not using electron multipliers is determined by the low space charge densities at which they must be operated to avoid instabilities associated with high random energy electrons. Lower temperature electron emitters will be required in measuring pressures below 10−13 Torr to avoid outgassing problems.
Discontinuous Au films on NaCl substrates
Authors: Goer D. , Dryer J. , Speiser R.
Published: July 2002

Electron micrographs of discontinuous Au films deposited on NaCl substrates have been obtained. Specimens include both films which have been subjected to externally applied voltages as well as films which have not had an external voltage applied. The micrographs offer direct photographic evidence of island distribution, size, and morphology which are highly supportive of injected charges affecting the film morphology in the vicinity of the electrodes.
Progress in extreme ultraviolet mask repair using a focused ion beam
Authors: Liang Ted , Stivers Alan , Livengood Richard , Yan Pei-Yang , Zhang Guojing , Lo Fu-Chang
Published: July 2002

The key challenge in extreme ultraviolet (EUV) mask defect repair is to avoid or limit the damage to the sensitive reflective multilayer (ML) stacks on the mask substrate and repair <55 nm mask defects. Our EUV mask design employs an oxide buffer layer between the ML and the absorber to protect the ML during repair. We have developed both opaque and clear EUV mask defect repair processes using focus ion beam (FIB) based gas-assisted etching (GAE) and ion-induced deposition. The process has been successfully demonstrated on our TiN baseline mask by 10× EUV print tests of 100 nm resist lines/spaces. More importantly we have assessed the current FIB tool performance capability and compared it with the general requirements for repairing the EUV mask for the 70 nm lithography node. The characterization includes minimum “effective” beam size, etch selectivity, and edge placement precision. We discussed the required improvements and future directions in repair tool research and development in order for the mask repair technology to keep pace with lithography scaling in future generations.
Study of the emission performance of carbon nanotubes
Authors: Wei Lei , Baoping Wang , Linsu Tong , Hanchun Yin , Yan Tu , Changchun Zhu
Published: July 2002

The carbon nanotube has good field emission properties, so it has been used as the electron source on the field emission display panel. To obtain a high emission current, the electric field at the tip of the nanotube must be large enough. This article studies the variation of electric field with different types of nanotubes. The emission current of the nanotube is also calculated for various geometrical parameters of nanotubes. From the simulation results, the influence of the geometrical parameters on the emission performance of nanotubes is studied.
Quantitative comparison between Auger electron spectroscopy and secondary ion mass spectroscopy depth profiles of a double layer structure of AlAs in GaAs using the mixing-roughness-information depth model
Authors: Hofmann S. , Rar A. , Moon D. W. , Yoshihara K.
Published: July 2002

Application of the so called mixing-roughness-information (MRI) depth model to quantitative reconstruction of the in-depth distribution of the composition is demonstrated by comparing secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) depth profiles. A GaAs/AlAs reference sample consisting of two layers of AlAs [1 and 36 monolayer (ML)] separated by 44 ML of a GaAs matrix was depth profiled using almost identical sputtering conditions: Ar+ ions of 3 keV impact energy and 52° (SIMS: CAMECA 4f ) and 58° (AES: VG Microlab 310F) incidence angle. Both the Al+ intensity of the SIMS profile and the Al (LVV) intensity of the AES profile were quantified by fitting the measured profiles with those calculated with the MRI model, resulting in the same mixing length of 3.0±0.3 nm, similar roughness parameter (1.4–2 nm), and negligible information depth (0.4 nm). Whereas practically no matrix effect was observed for AES as well as for Al+ in the SIMS profile, quantification using dimer (Al2+) and trimer (Al3+) ions shows a marked nonlinearity between concentration and intensity, with the main effect caused by the simple mass action law probability of cluster ion formation.
Level set approach to simulation of feature profile evolution in a high-density plasma-etching system
Authors: Im Y. H. , Hahn Y. B. , Pearton S. J.
Published: July 2002

The simulation of feature profile evolution in high-density plasma-etching processes has been carried out using a level-set technique. The main feature of this work is the inclusion of sheath dynamics, angular distribution of ions and reemission of neutrals in the trench, etch kinetics, and a level set equation for tracking a moving front of the feature profile. Sheath dynamics showed that the damped potential was somewhat shifted to the right and smaller than the applied potential. Etch profile simulations were performed for etching of silicon in inductively coupled plasmas of Cl2 and CF4 under various conditions. In dry etching of Si with CF4 discharges, polymer deposition was dominant at pCFx>10 mTorr, while surface fluorination (or ion-enhanced etching) was a main mechanism at pCFx<10 mTorr. The predicted etch profiles showed a slight bowing on the sidewalls and substantial tapering near the bottom, depending on the plasma parameters.
Experimental study of microcylindrical lenses fabricated using focused-ion-beam technology
Authors: Fu Yongqi , Bryan Ngoi Kok Ann
Published: July 2002

A new alternative manufacturing method using focused-ion-beam (FIB) technology is introduced in detail in this article. Fabrication of microcylindrical lenses can be realized based on SiO2 deposition and FIB milling. The former is suitable for fabricating directly on the surface of the microdevice. The latter is generally used for milling on chip-integrated microcomponents. The form accuracy can be precisely controlled by varying the parameters, such as the ion dose, accelerating voltage, beam current, etc. We analyzed in detail the influence of implanted Ga+ in the microlens and the precursor partial pressure of H2O and tetramethylcyclotetrasiloxane during the SiO2 microlens deposition on transmission. The experimental results and quality of the microlens using different methods are presented. We conclude that microfabrication of microcylindrical lenses using both FIB milling and deposition is practicable.
Time variation of the work function of field emitter tip surface and the development of adsorption of residual gas molecules studied by sawtoothlike emission current method
Authors: Yamamoto Youiti , Nagakura Sigemaro , Iwatsuki Masashi
Published: July 2002

The sawtoothlike emission current (STEC) method and its theory are described, and this method is shown to make possible the simultaneous measurement of the time variation of the work function φ(t) and its derivative dφ/dt. Application of the STEC method to the field emission (FE) current from a tungsten emitter tip in an ultra-high vacuum of 2×10−8 Pa shows that the time variation of φ(t) and dφ/dt can be divided into four stages. In addition, it gives the effective tip radius αr0=1.1 μm, resulting in α=6.9 for the observed tip radius r0=0.16 μm. The observed time variation of φ(t) and dφ/dt is analyzed from the viewpoint of the development of the adsorption of residual gas molecules on the emitter tip surface, and each stage is successfully identified as follows: The first stage is the formation stage of adsorption nuclei and clusters, the second stage is the free growth stage of adsorption islands, the third stage is their coalescence growth stage, and the fourth stage is their Langmuir growth stage. The mode of adsorption development is similar to the mode of crystal growth taking place in three-dimensional space and on surface.
XPS instrument coupled with ALCVD reactor for investigation of film growth
Authors: Sterner J. , Kessler J. , Stolt L.
Published: July 2002

A new tool for in situ x-ray photoelectron spectroscopy (XPS) analysis of the atomic layer chemical vapor deposition (ALCVD) process has been developed. Monitoring of the growth process is achieved by interconnecting an ALCVD reactor with an XPS analyzer. A basic experiment demonstrates the first in situ collected XPS data from the surface of each monoatomic layer of ZnO deposited in the ALCVD process. The method is able to resolve chemical changes as sequential layers evolve on the surface and will reveal critical parameters for the ALCVD process to work. Quantitative analysis of our results confirms the ALCVD theory.
Spatial distribution of reaction products in positive tone chemically amplified resists
Authors: Schmid Gerard M. , Stewart Michael D. , Singh Vivek K. , Willson C. Grant
Published: July 2002

The perpetual advancement of materials and equipment for microlithography has resulted in the ability to print critical dimensions that approach the size of the molecules that make up photoresists. As a result, molecular scale effects such as line edge roughness have become a concern for both resist manufacturers and process engineers. In this work we have investigated the increasing importance of molecular level effects, especially in terms of the contributions of the exposure and postexposure bake (PEB) steps to spatial variations in film composition. A mesoscale simulation of the PEB was used to model the discrete mass transport and reaction events that create the changes in film composition responsible for resist function. Local irregularities in resist composition are generated during the PEB, the magnitude of which can be related to the local concentration of acid. This study is focused on the establishment of an understanding of the effects of process and composition variables on the reaction product distribution. The reaction product distribution was calculated for an APEX®-like resist under a variety of exposure and bake conditions. These process variables have a profound influence on spatial irregularities in the composition gradient. Ultimately, it is the interaction of this reaction product distribution with the development process that will determine line edge roughness.