bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction: fragmentation and integration in knowledge management research
Authors: Gray Peter H. , Meister Darren B.
Published: September 2003

Knowledge management (KM) research lacks a common conceptual core; it is cross‐disciplinary, addresses a wide variety of phenomena, and has difficulty distinguishing itself from many related areas of research. The result is a fragmented field that is itself artificially split from the related literature on organizational learning. KM may be progressing through a predictable life‐cycle that could end in collapse of the KM concept unless researchers can develop more integrative core theories of learning‐ and knowledge‐related phenomena in organizations. The diverse body of organizational learning and knowledge management research provides an impressive foundation for the synthesis of such broader theories of learning and knowledge that are creative, new, and integrative.
Exploring uncertainty and emotion in the knowledge‐based theory of the firm
Authors: Spender J.‐C.
Published: September 2003

Uncertainty, managers’ frequent companion as they guide firms towards anticipated goals, is poorly dealt with in theories of the firm. If knowledge is to be treated as the most strategic of assets, we must consider its relation to uncertainty. Knowledge suggests a degree of certainty, an absence of uncertainty. The paper draws on prior research and categorize uncertainty as three types of knowledge deficiency: indeterminacy, ignorance and incommensurability. It is argued that uncertainties lead to emotion. The paper draws on analysis of emotions as value judgments, indicating a person attaches significance to things lying outside her/his control that affect her/his goals. This insight opens a way of relating knowledge and uncertainty. The impetus behind this approach is partly theoretical and partly personal, from observing and participating in New Yorkers’ emotions during and after the September 2001 WTC attacks. It is argued that it is no longer acceptable to ignore the ways in which emotion shapes our knowledge. The paper moves from rational self‐interest, the calculative basis for organization, to the social and cultural basis of identity through action, pursuing the idea that knowledge deficiencies produce emotional responses as they arrest rational decision making.
The challenge of knowledge management systems
Authors: Gallivan Michael J. , Eynon Jim , Rai Arun
Published: September 2003

Knowledge management systems and related initiatives have become a popular focus in many firms, yet many knowledge management systems initiatives fail to achieve their goals. Focuses on systems that are implemented to achieve deliberate performance improvement objectives in organizations, rather than to support discretionary communication. Employs constructs from system dynamics – a discipline that recognizes that the relationships between complex organizing technologies and human behavior are dynamic, evolving, and interconnected. Drawing from recent studies employing system dynamics, proposes a framework to analyze the implementation challenges posed by knowledge management systems adopted as part of a deliberate performance improvement program. Illustrates the framework with a case study of an initiative within a university “help desk” department where conflicting incentives hindered employees’ efforts to leverage the systems. The framework underscores the complex and interdependent effects triggered by managers’ actions and cognitions, in conjunction with users’ actions and cognitions. Offers insights for practitioners and researchers to recognize the downward spiral that can occur when conflicting incentives thwart the behavioral changes required for performance improvement initiatives to succeed.
Seasonality in tourism employment: human resource challenges
Authors: Jolliffe Lee , Farnsworth Regena
Published: September 2003

Seasonality in tourism has a profound impact on the management of human resources in organizations operating in a seasonal context. Tourism employment in Canada is profiled and its seasonality examined in Atlantic Canada, where seasonal tourism employment is common. A model for managing seasonality in employment is proposed as a continuum, ranging from “embracing” to “challenging” seasonality. For each approach, differing human resource management practices are identified and operational impacts are discussed, providing possible strategies for employers operating in seasonal tourism contexts. Ongoing research is planned in Atlantic Canada’s accommodations sector, testing the model for managing seasonal tourism employment.
Casino gaming and tourism in Canada
Authors: MacLaurin Tanya , MacLaurin Donald
Published: September 2003

This study provides background information on the casino gaming and tourism industries in Canada. The historical, regulatory, developmental, and subsequent growth to the present size and scope of the Canadian casino gaming industry is profiled. There are currently 64 full‐service casinos in Canada. Net revenue from government‐operated lotteries, video lottery terminals (VLTs) and casinos increased from $2.7 billion in 1990, to $9.0 billion in 2000, generating more then $5 billion in profits for Canadian governments. Employment in the gambling industry increased from 12,000 in 1992 to 41,000 in 2001. Casino gaming is currently the fastest‐growing component of the Canadian tourism industry. Current Canadian casino gaming markets are identified and suggestions made for possible future directions in this high growth industry.
Strategic issues faced by Ontario hotels
Authors: Lu Zhen , Chiang Denise
Published: September 2003

Limited research exists on the current strategic issues and the strategies utilized by hoteliers of Ontario, Canada. The researchers conducted a pilot study by utilizing an e‐mail survey, attempting to identify the current strategic issues and strategies implemented by Ontario hotels. The results showed that the most concerned issues by the Ontario hoteliers are: lacking financial and government support, changing customer needs, increasing power of customer purchasing through the internet and the top Internal environment concern is related to the human resources. The survey findings suggest the imperative requirement for awareness and focus of the changing environmental variables affecting the Ontario lodging industry.
People and quality: the case of Delta Hotels
Authors: Pallet William J. , Taylor Wayne W. , Jayawardena Chandana
Published: September 2003

Analyses the concept of quality in the hotel industry. Emphasises that quality has to be a part of the culture of an organisation. Presents Delta Hotels in Canada as an exemplary case study in relation to people and quality initiatives. Delta has, over the years, built a good reputation and currently ranks as the best hotel company to work for in Canada. Presents the companys’ vision, mission and philosophies for people and quality. Lists nine key quality principles and four people resource systems and outcomes. Concludes by making ten recommendations to hotel companies considering implementing effective people and quality concepts.
A pioneering spirit: using administrative metadata to manage electronic resources
Authors: Medeiros Norm
Published: September 2003

This article describes administrative metadata and their use in managing electronic resources. The focus of the article is an interview with Tim Jewell, Head of Collection Management Services at the University of Washington, and Adam Chandler, Information Technology Librarian at Cornell University.
Archives and memory
Authors: Jimerson Randall C.
Published: September 2003

Archives are repositories of memory, providing reliable evidence for examining the past. The four types of memory – personal, collective, historical, and archival – interact in complex and sometimes baffling ways to enable one to understand the past and to draw lessons from it. Archival memory is a social construct reflecting power relationships in society. Archivists and manuscripts curators play the important role of mediator in selecting records for preservation and providing research access to such collections. By recognizing and overcoming the bias toward records of powerful groups in society, archivists can provide a more balanced perspective on the past, and enable future generations to examine and evaluate the activities and contributions of all voices in one’s culture. Archives thus serve an important role in identifying and preserving the documentation that forms one’s historical memory.
Subject headings for OCLC rare book records: a case study
Authors: McClellan Edna
Published: September 2003

This study presents an overview of the quality of 232 OCLC rare book cataloging records. Of the 232 records, 31 that needed subject headings were not provided with any. A total of 791 headings, including main headings (428) and subdivision headings (363), were examined and 69 discrepancies were found. The discrepancies were mainly obsolete headings. The error rate was 9 per cent. Only one typographical error was found. Moreover, 95 per cent (191) of the 201 records had been replaced at least once but the discrepancy rate remained very high at 8 per cent. Since the records examined were not randomly selected and the sample size was small, the result of this study cannot be generalized. However, the overall results indicate that the quality of OCLC rare book records need attention as much as, if not more than, other records.
A Web‐based document distribution system constructed with Lotus Notes
Authors: Cummings Roger
Published: September 2003

This article describes practical solutions to problems encountered over more than five years of operating a fully automated Web‐based digital document submission, registration, and distribution system. The author began creating the system in 1997 to support the activities of a Technical Committee of the International Committee for Information Technology Standardization (INCITS). Since then, the system has received continual enhancement and expansion. The register now contains more than 8,000 documents submitted by Committee participants, stored as PDF files occupying more than 4 gigabytes of storage, which interested parties world‐wide regularly access. A similar architecture and document registration system could be used to support any physically dispersed group cooperating on any type of project. The library is located on a public Web site and readers are encouraged to access it.
Digital library development in Brazil
Authors: McCarthy Cavan , Bastos da Cunha Murilo
Published: September 2003

The Internet came to Brazil early, and was quickly recognized as an exciting new means of communication, highly appropriate for a technologically advanced and recently democratized society. This paper identifies and characterizes the principal Brazilian digital library initiatives in science and research; education; literature and the humanities and history and politics. Government financing was critical for the implementation of Brazilian digital libraries. Institutions with a strong background in advanced technology had an advantage when entering the digital library field. Cooperative projects have also had significant impact.
RCM introduction: process and requirements management aspects
Authors: Backlund F. , Akersten P.A.
Published: September 2003

Organisations have introduced reliability‐centred maintenance (RCM) with a view to changing their overall way of performing maintenance. Many times, however, these organisations have experienced cumbersome or even failed RCM introduction. This is usually because of managerial and organisational obstacles, which more or less unexpectedly turn up during introduction. This paper focuses on managing the introduction of RCM. By applying process and requirement management principles, obstacles that turn up during introduction can be identified early on. As an example of this, we cite the results of a case study of the introduction of RCM in a Swedish hydropower company.
Estimating the mixture of proportional hazards model with incomplete failure data
Authors: Woon Kim Jong , Young Yun Won , Dohi Tadashi
Published: September 2003

Cox’s proportional hazards model (PHM) has been widely applied to the analysis of lifetime data. It involves covariates influencing the failure of products. Regarding the covariates as discrete random variables, the probability model is reduced to a mixture of PHM. This article presents a statistical procedure to estimate model parameters in the mixture of PHM. The estimation procedure is developed in a parametric framework when not only complete sets of field data but also incomplete ones are given. The expectation‐maximization algorithm is employed to handle the incomplete data problem. Simulation results are presented to illustrate the accuracy and some properties of the estimation results.
Repair times for systems that have high early failures
Authors: Sherif Joseph S.
Published: September 2003

Active repair time is that portion of down time during which the system is worked on to effect a repair. Repair time includes preparation time, diagnostic time, correction time and final checkout time. Systems such as airborne communications transceivers, switching circuits and radar‐missile units usually suffer an initial high rate of wear and failure. Improvement in this area requires actions to reduce the frequency of failure and to increase ease of repair. This paper advances the first passage time distribution of Brownian motion as a repairability model. The paper fits the model to observed active repair time of radar systems, obtaining as a result estimates of the mean first passage time, drift and diffusion parameters of the associated Brownian motion. Hypothesizing the first passage time distribution of Brownian motion for active repair time data of radar systems, the Kolmogorov‐Smirnov test shows that the model is accepted and can be chosen as the parent population.
Probabilistic safety analysis of maintainable systems
Authors: Dhillon B.S. , Kirmizi Fahri
Published: September 2003

This paper presents two mathematical models to perform probabilistic safety analysis in maintenance environment. Both models assume system operating in safe and unsafe environments. Model I represents a repairable system with three states: working normally, working in unsafe mode, and failed safely. Model II represents a repairable system with four states: working normally, working in unsafe mode due to human error, working in unsafe mode due to hardware failure, and failed safely. Equations for state probabilities, system availabilities, reliability, and mean time to failure are developed.
Using integrated spreadsheet modeling for supply chain analysis
Authors: Smith Gary A.
Published: September 2003

Spreadsheet software, notably Microsoft Excel, can be used very effectively for analyzing logistics and supply chain issues. Spreadsheets allow analysis from many different perspectives and can be modified and enhanced to reflect new situations and options. The methodology used for developing integrated spreadsheet models is similar to modeling with specialized software. The modeler develops a baseline model reflecting current operations, creates alternative scenarios and compares those scenarios to the baseline. Non‐quantifiable factors and soft costs are also considered to develop a complete analysis. Using integrated spreadsheets the modeler can analyze the impact of business decisions on any number of variables such as facility space, inventory, investment and productivity.
On‐line trust building in e‐enabled supply chain
Authors: Agarwal Ashish , Shankar Ravi
Published: September 2003

Trust is a binding force in most buyer‐supplier transactions. It is critical when uncertainty and asymmetric product information are present in the transaction of a supply chain. One of the important characteristics in developing trust among trading partners of an e‐enabled supply chain is stage‐wise trust development among partners. In the present work, alternatives for trust development among buyer and supplier have been identified. In order to evaluate the alternatives to evolve trust in an e‐enabled supply chain, a framework involving analytic networked process is proposed. It helps in synthesizing various characteristics of trust in the e‐enabled supply chain. For the illustrative example, the result indicates superiority of a community responsibility system for building on‐line trust along the e‐enabled supply chain.
Factors affecting the development of national quality awards
Authors: Tan Kay C. , Wong Mei F. , Mehta Teena , Khoo Hsien H.
Published: September 2003

After the successful launch of the Malcolm Baldrige National Quality Award (MBNQA) and European Quality Award (EQA), the governing authorities of many other countries have begun establishing their own national quality award (NQA) programs. Most NQA models are based on the MBNQA and EQA. Other NQA models choose to be unique. This paper compiles differences in the modeling of 53 NQAs found around the world. From the compilation is derived a set of recommended guidelines for the establishment and further development of NQAs. The guidelines include suggestions for either starting up or enhancing existing NQA programs in both developed and developing countries.
Study of the adjustment of Western expatriates in Taiwan ROC with the Multicultural Personality Questionnaire
Authors: van Oudenhoven Jan Pieter , Mol Stefan , Van der Zee Karen I.
Published: September 2003

The present paper examined the validity of the Multicultural Personality Questionnaire (MPQ). As criteria of validity three levels of adjustment were used. The study took place among a sample of expatriates (N = 102) during their assignment in Taiwan. The MPQ has scales for cultural empathy, open‐mindedness, social initiative, emotional stability and flexibility. The MPQ scales appeared to be predictive of expatriates’ personal, professional and social adjustment. In all three domains, emotional stability appeared most consistently as a predictor of adjustment. Social initiative was an additional strong predictor of psychological well‐being, as was cultural empathy of satisfaction with life and of the amount of social support in the host country. Flexibility was a predictor of job satisfaction and social support. The study also examined the effects of marital status on adjustment. Married expatriates showed higher levels of adjustment than expatriates who were single or separated.
Market‐based Organizational Learning and Market Performance Gains
Authors: Morgan Robert E. , Turnell Christopher R.
Published: September 2003

Building upon the market orientation‐performance thesis, many investigators are now concerned with broader organizational learning considerations and the antecedents that underlie the analytical properties of learning about competitors and markets. Described as a process of market‐based organizational learning, an empirical test of a model is provided which indicates that: when organizations exhibit more favourable learning values (three value‐based constructs), their market information processing behaviours and analytical capabilities improve (three knowledge‐based constructs), which thereby directly impacts upon market‐based outcomes (a market performance construct) that the organization is able to generate. This model is tested with a path‐analytic approach from data generated in the UK financial services industry. Discussion of these findings is made in the light of pertinent literature streams, and several implications for future research are provided.
Price Commitment versus Flexibility: the Role of Exchange Rate Uncertainty and its Implications for Exchange Rate Passthrough
Authors: Chang Byoung‐Ky , Lapan Harvey E.
Published: September 2003

The paper investigates the incentives to commit price or retain price flexibility in a model in which exporting firms face different degrees of exchange rate uncertainty. The result shows that introducing exchange rate uncertainty can lead to the endogenous emergence of a unique leader–follower equilibrium; which firm emerges as price leader depends on the substitutability of products, the magnitude of exchange rate uncertainty, and the cost structure. This study may provide one explanation as to why some exporters set price before the realization of the nominal exchange rates (“sticky price”). The results imply exchange rate variability affects exchange rate passthrough.
A Latent Gaussian Markov Random-Field Model for Spatiotemporal Rainfall Disaggregation
Authors: Allcroft David J. , Glasbey Chris A.
Published: September 2003

Rainfall data are often collected at coarser spatial scales than required for input into hydrology and agricultural models. We therefore describe a spatiotemporal model which allows multiple imputation of rainfall at fine spatial resolutions, with a realistic dependence structure in both space and time and with the total rainfall at the coarse scale consistent with that observed. The method involves the transformation of the fine scale rainfall to a thresholded Gaussian process which we model as a Gaussian Markov random field. Gibbs sampling is then used to generate realizations of rainfall efficiently at the fine scale. Results compare favourably with previous, less elegant methods.
Transitions Off Welfare: An Examination of Demographic, Socioeconomic, and Motivational Predictors
Authors: Stellmack Amy L. , Wanberg Connie R. , Kammeyer‐mueller John
Published: September 2003

A three‐wave longitudinal study of 1071 female Minnesota Family Investment Program (MFIP) recipients was conducted to examine predictors of welfare outcomes in the context of the 1996 federal welfare reform act. In addition to the demographic and socioeconomic variables that typically have been examined in the welfare literature, motivational variables (i.e., achievement motivation and goal commitment) that have been touted to be important by the popular press and in qualitative studies but never systematically measured were examined.
The polyphonic spree: the case of the Liverpool Dockers
Authors: Carter Chris , Clegg Stewart , Hogan John , Kornberger Martin
Published: September 2003

This paper is concerned with the possibilities opened up for Trade Unions by the internet age. The paper analyses forms of resistance, their preconditions and organisational backgrounds. It is argued that polyphonic organisation and, closely linked, new organisational forms, provide a strong basis for power relations and strategies of resistance. The paper starts with a brief introduction to the dispute between the Dockers of Liverpool and the Mersey Docks and Harbour Company. Contextualising the evolving issue in the broader picture of trade union crisis and renewal, the case study is theorised using linguistically informed approaches to management and organisation theory. Introducing these theoretical developments, the potential of new organisational forms for power relations and resistance are elaborated.
The Prp19p-Associated Complex in Spliceosome Activation
Authors: Chan Shih-Peng , Kao Der-I , Tsai Wei-Yü , Cheng Soo-Chen
Published: September 2003

During spliceosome activation, a large structural rearrangement occurs that involves the release of two small nuclear RNAs, U1 and U4, and the addition of a protein complex associated with Prp19p. We show here that the Prp19p-associated complex is required for stable association of U5 and U6 with the spliceosome after U4 is dissociated. Ultraviolet crosslinking analysis revealed the existence of two modes of base pairing between U6 and the 5′ splice site, as well as a switch of such base pairing from one to the other that required the Prp19p-associated complex during spliceosome activation. Moreover, a Prp19p-dependent structural change in U6 small nuclear ribonucleoprotein particles was detected that involves destabilization of Sm-like (Lsm) proteins to bring about interactions between the Lsm binding site of U6 and the intron sequence near the 5′ splice site, indicating dynamic association of Lsm with U6 and a direct role of Lsm proteins in activation of the spliceosome.
Experimental Determination and System Level Analysis of Essential Genes in
Escherichia coli
MG1655
Authors: Gerdes S. Y. , Scholle M. D. , Campbell J. W. , Balázsi G. , Ravasz E. , Daugherty M. D. , Somera A. L. , Kyrpides N. C. , Anderson I. , Gelfand M. S. , Bhattacharya A. , Kapatral V. , D'Souza M. , Baev M. V. , Grechkin Y. , Mseeh F. , Fonstein M. Y. , Overbeek R. , Barabási A.-L. , Oltvai Z. N. , Osterman A. L.
Published: September 2003

Defining the gene products that play an essential role in an organism's functional repertoire is vital to understanding the system level organization of living cells. We used a genetic footprinting technique for a genome-wide assessment of genes required for robust aerobic growth of
Escherichia coli
in rich media. We identified 620 genes as essential and 3,126 genes as dispensable for growth under these conditions. Functional context analysis of these data allows individual functional assignments to be refined. Evolutionary context analysis demonstrates a significant tendency of essential
E. coli
genes to be preserved throughout the bacterial kingdom. Projection of these data over metabolic subsystems reveals topologic modules with essential and evolutionarily preserved enzymes with reduced capacity for error tolerance.
VGJφ, a Novel Filamentous Phage of
Vibrio cholerae
, Integrates into the Same Chromosomal Site as CTXφ
Authors: Campos Javier , Martínez Eriel , Suzarte Edith , Rodríguez Boris L. , Marrero Karen , Silva Yussuan , Ledón Talena , del Sol Ricardo , Fando Rafael
Published: September 2003

We describe a novel filamentous phage, designated VGJφ, isolated from strain SG25-1 of
Vibrio cholerae
O139, which infects all O1 (classical and El Tor) and O139 strains tested. The sequence of the 7,542 nucleotides of the phage genome reveals that VGJφ has a distinctive region of 775 nucleotides and a conserved region with an overall genomic organization similar to that of previously characterized filamentous phages, such as CTXφ of
V. cholerae
and Ff phages of
Escherichia coli
. The conserved region carries 10 open reading frames (ORFs) coding for products homologous to previously reported peptides of other filamentous phages, and the distinctive region carries one ORF whose product is not homologous to any known peptide. VGJφ, like other filamentous phages, uses a type IV pilus to infect
V. cholerae
; in this case, the pilus is the mannose-sensitive hemagglutinin. VGJφ-infected
V. cholerae
overexpresses the product of one ORF of the phage (ORF112), which is similar to single-stranded DNA binding proteins of other filamentous phages. Once inside a cell, VGJφ is able to integrate its genome into the same chromosomal
attB
site as CTXφ, entering into a lysogenic state. Additionally, we found an
attP
structure in VGJφ, which is also conserved in several lysogenic filamentous phages from different bacterial hosts. Finally, since different filamentous phages seem to integrate into the bacterial
dif
locus by a general mechanism, we propose a model in which repeated integration events with different phages might have contributed to the evolution of the CTX chromosomal region in
V. cholerae
El Tor.
The Membrane-Associated Methane Monooxygenase (pMMO) and pMMO-NADH:Quinone Oxidoreductase Complex from
Methylococcus capsulatus
Bath
Authors: Choi Dong-W. , Kunz Ryan C. , Boyd Eric S. , Semrau Jeremy D. , Antholine William E. , Han J.-I. , Zahn James A. , Boyd Jeffrey M. , de la Mora Arlene M. , DiSpirito Alan A.
Published: September 2003

Improvements in purification of membrane-associated methane monooxygenase (pMMO) have resulted in preparations of pMMO with activities more representative of physiological rates: i.e., >130 nmol · min
−1
 · mg of protein
−1
. Altered culture and assay conditions, optimization of the detergent/protein ratio, and simplification of the purification procedure were responsible for the higher-activity preparations. Changes in the culture conditions focused on the rate of copper addition. To document the physiological events that occur during copper addition, cultures were initiated in medium with cells expressing soluble methane monooxygenase (sMMO) and then monitored for morphological changes, copper acquisition, fatty acid concentration, and pMMO and sMMO expression as the amended copper concentration was increased from 0 (approximately 0.3 μM) to 95 μM. The results demonstrate that copper not only regulates the metabolic switch between the two methane monooxygenases but also regulates the level of expression of the pMMO and the development of internal membranes. With respect to stabilization of cell-free pMMO activity, the highest cell-free pMMO activity was observed when copper addition exceeded maximal pMMO expression. Optimization of detergent/protein ratios and simplification of the purification procedure also contributed to the higher activity levels in purified pMMO preparations. Finally, the addition of the type 2 NADH:quinone oxidoreductase complex (NADH dehydrogenase [NDH]) from
M. capsulatus
Bath, along with NADH and duroquinol, to enzyme assays increased the activity of purified preparations. The NDH and NADH were added to maintain a high duroquinol/duroquinone ratio.
The
Geobacillus stearothermophilus
V
iscS
Gene, Encoding Cysteine Desulfurase, Confers Resistance to Potassium Tellurite in
Escherichia coli
K-12
Authors: Tantaleán Juan C. , Araya Manuel A. , Saavedra Claudia P. , Fuentes Derie E. , Pérez José M. , Calderón Iván L. , Youderian Philip , Vásquez Claudio C.
Published: September 2003

Many eubacteria are resistant to the toxic oxidizing agent potassium tellurite, and tellurite resistance involves diverse biochemical mechanisms. Expression of the
iscS
gene from
Geobacillus stearothermophilus
V, which is naturally resistant to tellurite, confers tellurite resistance in
Escherichia coli
K-12, which is naturally sensitive to tellurite. The
G. stearothermophilus iscS
gene encodes a cysteine desulfurase. A site-directed mutation in
iscS
that prevents binding of its pyridoxal phosphate cofactor abolishes both enzyme activity and its ability to confer tellurite resistance in
E. coli
. Expression of the
G. stearothermophilus iscS
gene confers tellurite resistance in tellurite-hypersensitive
E. coli iscS
and
sodA sodB
mutants (deficient in superoxide dismutase) and complements the auxotrophic requirement of an
E. coli iscS
mutant for thiamine but not for nicotinic acid. These and other results support the hypothesis that the reduction of tellurite generates superoxide anions and that the primary targets of superoxide damage in
E. coli
are enzymes with iron-sulfur clusters.
Identification of Three Genes Encoding P
II
-Like Proteins in
Gluconacetobacter diazotrophicus
: Studies of Their Role(s) in the Control of Nitrogen Fixation
Authors: Perlova Olena , Ureta Alejandro , Nordlund Stefan , Meletzus Dietmar
Published: September 2003

In our studies on the regulation of nitrogen metabolism in
Gluconacetobacter diazotrophicus
, an endophytic diazotroph of sugarcane, three
glnB
-like genes were identified and their role(s) in the control of nitrogen fixation was studied. Sequence analysis revealed that one P
II
protein-encoding gene,
glnB
, was adjacent to a
glnA
gene (encoding glutamine synthetase) and that two other P
II
protein-encoding genes, identified as
glnK1
and
glnK2
, were located upstream of
amtB1
and
amtB2
, respectively, genes which in other organisms encode ammonium (or methylammonium) transporters. Single and double mutants and a triple mutant with respect to the three P
II
protein-encoding genes were constructed, and the effects of the mutations on nitrogenase expression and activity in the presence of either ammonium starvation or ammonium sufficiency were studied. Based on the results presented here, it is suggested that none of the three P
II
homologs is required for
nif
gene expression, that the GlnK2 protein acts primarily as an inhibitor of
nif
gene expression, and that GlnB and GlnK1 control the expression of
nif
genes in response to ammonium availability, both directly and by relieving the inhibition by GlnK2. This model includes novel regulatory features of P
II
proteins.
Tethering of the
Bacillus subtilis
σ
E
Proprotein to the Cell Membrane Is Necessary for Its Processing but Insufficient for Its Stabilization
Authors: Ju Jingliang , Haldenwang W. G.
Published: September 2003

σ
E
, a sporulation-specific transcription factor of
Bacillus subtilis
, is synthesized as an inactive proprotein with a 27-amino acid extension at its amino terminus. This “pro” sequence is removed by a developmentally regulated protease, but when present, it blocks σ
E
activity, tethers σ
E
to the bacterium's cytoplasmic membrane, and promotes σ
E
stability. To investigate whether pro-σ
E
processing and/or stabilization are tied to membrane sequestration, we used fluorescent protein fusions to examine the membrane binding of SigE variants. The results are consistent with membrane association as a prerequisite for pro-σ
E
processing but not as a sufficient cause for the proprotein's stability.
Doping Dependence of Bose Condensation Energy in High Tc Cuprates
Authors: Lee Sung-Sik , Salk Sung-Ho Suck
Published: September 2003

The doping dependence of the bose condensation energy is investigated by using our SU (2) holon-pair boson theory. It is shown that the bose condensation energy U results from the interplay between the charge and spin degrees of freedom and that the doping dependence of U at T=0K is well fit by the relation, [Formula: see text] with Δ0, the spin gap at 0K; x, the hole doping concentration and α, a constant.
Electron-Hole Asymmetry is the Key to Superconductivity
Authors: Hirsch J. E.
Published: September 2003

In a solid, transport of electricity can occur via negative electrons or via positive holes. In the normal state of superconducting materials experiments show that transport is usually dominated by dressed positive hole carriers. Instead, in the superconducting state experiments show that the supercurrent is always carried by undressed negative electron carriers. These experimental facts indicate that electron-hole asymmetry plays a fundamental role in superconductivity, as proposed by the theory of hole superconductivity.
Effects of Incomplete Superconducting Condensation on Electron Tunneling
Authors: Kim Ju H.
Published: September 2003

We studied the tunnel junctions of s-wave superconductors in the presence of nonmagnetic impurities and uncondensed quasiparticles. Contrary to general belief, we found that the tunneling conductance in an SIN junction made of strong-coupling superconductors is modified by uncondensed quasiparticles. Also, the Josephson current in an SIS junction can be drastically reduced by these particles from the standard result of Ambegaokar and Baratoff. In weak-coupling superconductors, the conventional junction behaviors are restored.
Superlight High Tc Bipolarons in Cuprates
Authors: Alexandrov A. S.
Published: September 2003

Most of the proposed models of high-temperature superconductivity (HTSC) are based on the short-range electron-electron correlations or/and on a short-range electron-phonon interaction. However, in the cuprates the screening is poor due to a low carrier density, layered crystal structure, and high ionicity of the lattice. We develop further the bipolaron model of HTSC, which explicitly takes into account the long-range origin of all interactions. The long-range electron-phonon (Fröhlich) interaction binds carriers into real space pairs (small bipolarons) with surprisingly low mass but sufficient binding energy, while the long-range Coulomb repulsion keeps them from forming larger clusters. The model has explained many key features of cuprates. It is shown here that real-space pairing takes place in many cuprates at variance with some (incorrect) criteria of the BCS-BEC crossover.
From Charge Transfer Type Insulator to Superconductor
Authors: Guo Wei , Han Rushan
Published: September 2003

We propose a microscopic model Hamiltonian to account for impurity doping induced insulator-superconductor transition and the coexistence of antiferromagnetism and superconductivity in the high-Tc cuprates. The crossover from non Fermi liquid to Fermi liquid regime characterized by delocalization of d electrons on Cu sites is discussed.
Pertubation Theory About Self-Consistent Field Solution in One-Dimensional Hubbard Model
Authors: Kocharian A. N. , Yang C. , Chiang Y. L.
Published: September 2003

The accurate analytical and numerical calculations of the electronic band structure and ground state properties of strongly correlated electrons within the Hubbard model are performed by constructing convergent perturbation theory for general interaction strength and electron concentration. We test the developed perturbation approach about mean field solution in the extreme conditions of one dimensionality for entire parameter space of electron interaction U/t and electron concentration n. The many-body perturbation formalism up two second order about the generalized self-consistent field (GSCF) Hamiltonian goes beyond the range of applicability of standard perturbation theory by incorporating systematically the effect of the random-phase-type perturbation techniques and controlled expansion of the energy functional for general U/t and n. The second order perturbation correction vanishes at small and large U/t limit and performed calculations of the ground state energy show a next to the perfect numerical agreement with the Bethe-ansatz results.
Asymmetry in the Hole-Doped and Electron-Doped t-J Model
Authors: Leung P. W. , Ng K. K.
Published: September 2003

We model electron-doped high Tc materials using the t-t′-t′′-J model. This model is solved on a cluster with 32 sites using the method of exact diagonalization. Our purpose is to study the symmetry and asymmetry between hole- and electron-doped high Tc materials by comparing the results with those of the t-J model. In the electron-doped model with one charge carrier, we find a strong quasiparticle peak at (π,0). Compared to the t-J model, the bandwidth is larger, reflecting the fact that the charge carrier moves more freely in the electron-doped model. In the two-carrier model the ground state has robust dx2-y2 symmetry. This is in contrary to the two-hole t-J model whose ground state is a competition between low-energy states with dx2-y2 and p symmetries. The spatial distribution function of the carriers shows that they move almost freely on different sublattices.
Flux Dynamics and Vortex Phase Diagram in Tl2Ba2CaCu2O8 System
Authors: Chowdhury P. , Kim Heon-Jung , Lee Sung-Ik
Published: September 2003

Experimental data on the field and time dependencies of the isothermal magnetization hysteresis for Tl 2 Ba 2 CaCu 2 O 8 single crystals with fields applied parallel to the c-axis are reported. From the M–H measurements, we determined the first peak field (Hp), the onset field of the second peak (Hon), the second peak field (Hsp), and the irreversible field (Hirr). Using these physical parameters, we have drawn a vortex phase diagram for this system. As observed in BSCCO(2212) system, below the irreversibility line, the H–T plane is divided into three distinct phases: the vortex lattice, the entangle phase, and the quasi 2D pancake vortex states in the temperature interval 30 K ≤T≤60 K .1 From the relaxation of remanent magnetization measurements, we have obtained the flux creep activation barrier U(j) as a function of j using the method developed by Malay et al. Within the collective pinning theory, it is argued that T≤30 K , the pancake vortices are pinned individually, while for T≥42 K , the vortex state is characterized by individually pinned 3D vortex strings. At T~30 K , a crossover from 2D pancake to 3D collectively pinned state was observed and shows a smooth crossover to 3D single vortex state at higher temperatures.
Photoemission, Correlation and Superconductivity: New Avenues
Authors: Abrecht M. , Ariosa D. , Cloëtta D. , Pavuna D. , Perfetti L. , Grioni M. , Margaritondo G.
Published: September 2003

We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.
Extended Quasiparticle States Outside the Vortex Cores in a d-Wave Superconductor
Authors: Zheng Guo-Qing
Published: September 2003

We a describe a measurement of the spin Knight shift (Ks) around the middle point between two vortices as a function of magnetic field (H) up to 28 T in a high-Tc superconductor TlSr 2 CaCu 2 O 6.8. At low temperatures, Ks increases substantially with increasing field, which indicates that the quasiparticle states with an ungapped spectrum are extended outside the vortex cores in a d-wave superconductor. The density of such states is found to be [Formula: see text], with N0 being the normal-state density of states and Hc2 being the upper critical field.
Effect of an In-Plane Magnetic Field on the Interlayer Phase Coherence in the Extreme-2D Organic Superconductor κ-(BEDT-TTF)2Cu(NCS)2
Authors: Kovalev A. E. , Takahashi S. , Hill S. , Qualls J. S.
Published: September 2003

Using a high-sensitivity cavity perturbation technique (40 to 180 GHz), we have probed the angle dependent interlayer magneto-electrodynamic response within the vortex state of the extreme two-dimensional organic superconductor κ- (BEDT-TTF) 2 Cu(NCS) 2. A previously reported Josephson plasma resonance [M. Mola et al., Phys. Rev.B62, 5965 (2000)] exhibits a dramatic re-entrant behavior for fields very close (< 1°) to alignment with the layers. In this same narrow angle range, a new resonant mode develops which appears to be associated with the non-equilibrium critical state. Fits to the angle dependence of the Josephson plasma resonance provide microscopic information concerning the superconducting phase correlation function within the vortex state. We also show that the effect of an in-plane magnetic field on the temperature dependence of the interlayer phase coherence is quite different from what we have previously observed for perpendicular magnetic fields.
Low Energy Excitation in Bi2Sr2Can-1CunO2n+4 (n = 1-3) Studied by High-Resolution Arpes
Authors: Matsui H. , Sato T. , Takahashi T. , Yang H.-B. , Wang S.-C. , Ding H. , Fujii T. , Watanabe T. , Matsuda A. , Terashima T. , Kadowaki K.
Published: September 2003

We report systematic high-resolution angle-resolved photoemission spectroscopy (ARPES) on Bi 2 Sr 2 Ca n-1 Cu n O 2n+4 (n = 1-3) to study the electronic structure near the Fermi level (EF) and the low energy excitation. Comprehensive ARPES data on the sudden break in the energy dispersion near EF (kink) as a function of momentum, temperature, and number of CuO 2 layers indicate that the coupling of electrons with Q = (π,π) magnetic mode is dominant in the superconducting state for multi-layered cuprates.
Verification of Nodeless Superconducting Pairing in Single-Crystal YBa2Cu3O7
Authors: Harshman Dale R. , Kossler W. J. , Wan X. , Fiory A. T. , Greer A. J. , Noakes D. R. , Stronach C. E. , Koster E. , Erb A. , Dow John D.
Published: September 2003

The temperature and field dependence of the penetration depth was determined from muon spin rotation (μ+ SR ) measurements on a single crystal of YBa 2 Cu 3 O 7 having a superconducting transition at Tc ≈ 91.3 K . Data were acquired at applied magnetic fields of 0.05, 1.0, 3.0, and 6.0 Tesla, yielding results inconsistent with any pairing state requiring nodes, including d-wave pairing. These data are, however, completely consistent with s-wave (or extended s-wave) superconductivity, with clear evidence of field-dependent, temperature-activated vortex pinning. Our results confirm the s-wave character originally observed in 1989, and show that the features of μ+ SR (and microwave) data used by other authors as evidence for d-wave superconductivity are instead due to temperature- and field-dependent vortex pinning/reordering, resulting in significant distortion of the flux lattice.
Occurrence of Superconductivity in Ba-Doped NdSr2(Cu,Mo)3Oz
Authors: Lee H. K. , Kim K. D.
Published: September 2003

Polycrystalline samples of Nd ( Sr 2-y Ba y)( Cu 3-x Mo x) O z (0 ≤ y ≤ 0.5, 0.1 ≤ x ≤ 0.3) with tetragonal structure were synthesized and investigated by powder X-ray diffraction, electrical resistivity, magnetic susceptibility and thermoelectric power measurements. Contrary to the absence of superconductivity of the Ba-free samples, superconductivity can be achieved by partially substituting Ba for Sr in semiconducting NdSr 2( Cu 3-x Mo x) O z (0.15 ≤ x ≤ 0.3). Thermoelectric power measurements reveal that all the samples are in the underdoped state and the partial substitution of Ba for Sr results in an increase of the carrier density on the superconducting layers.
Photoinduced Conductivity Dynamics Studies of MgB2 Thin Films
Authors: Demsar Jure , Averitt Richard D. , Taylor Antoinette J. , Kang Won-Nam , Kim Heon Jung , Choi Eun-Mi , Lee Sung-Ik
Published: September 2003

We present the first direct studies of photoinduced Cooper-pair breaking and subsequent superconducting state recovery dynamics by means of femtosecond time-resolved optical-pump terahertz probe spectroscopy focusing on the superconducting state recovery dynamics in MgB 2. The superconducting state recovery proceeds on the timescale of several hundred picoseconds and shows a strong temperature dependence. In particular, upon increasing the temperature the recovery time first decreases, reaches a minimum, followed by a quasi-divergence upon further increasing the temperature towards Tc. Moreover, the recovery time shows virtually no intensity dependence, even though the photoexcitation fluence is changed by over an order of magnitude. This suggests that pair recovery is goverend by a phonon-bottleneck mechanism, where the lifetime of high energy phonons (ℏω > 2Δ) is governed by their anharmonicity.
Superconducting and Magnetic Properties of (Ru1-xNbx)Sr2(Eu1.5Ce0.5)Cu2Oz
Authors: Lee H. K. , Kim Y. C.
Published: September 2003

The ( Ru 1-x Nb x) Sr 2( Eu 1.5 Ce 0.5) Cu 2 O z(0 ≤ x ≤ 0.5) compounds have been synthesized and characterized by X-ray diffraction, electric transport, and magnetic susceptibility measurements. We find that there is no significant change in the superconducting transition temperature when Nb is substituted for Ru up to x = 0.5. Unlike RuSr 2( Eu 1.5 Ce 0.5) Cu 2 O z, bulk Meissner effect is observed in the field-cooled magnetization measurements of the Nb doped samples. The experimental results are discussed in conjunction with a reduction of the internal field caused by the Nb substitution for Ru, based on the spontaneous vortex phase interpretation.
Improved Epitaxy and Surface Morphology in YBa2Cu3Oy Thin Films Grown on Double Buffered Si Wafers
Authors: Gao J. , Kang L. , Wong H. Y. , Cheung Y. L. , Yang J.
Published: September 2003

Highly epitaxial thin films of YBCO have been obtained on silicon wafers using a Eu 2 CuO 4/ YSZ (yttrium-stabilized ZrO 2) double buffer. Our results showed that application of such a double buffer can significantly enhance the epitaxy of grown YBCO. It also leads to an excellent surface morphology. The average surface roughness was found less than 5 nm in a large range. The results of X-ray small angle reflection and positron spectroscpy demonstrate a very clear and flat interface between YBCO and buffer layers. The Eu 2 CuO 4/ YSZ double buffer could be promising for coating high-TC superconducting films on various reactive substrates.