bluuebunny/crossref_metadata_2025 huggingface dataset:
On the optimality of the neighbor-joining algorithm
Authors: Eickmeyer Kord , Huggins Peter , Pachter Lior , Yoshida Ruriko
Published: April 2008

The popular neighbor-joining (NJ) algorithm used in phylogenetics is a greedy algorithm for finding the balanced minimum evolution (BME) tree associated to a dissimilarity map. From this point of view, NJ is "optimal" when the algorithm outputs the tree which minimizes the balanced minimum evolution criterion. We use the fact that the NJ tree topology and the BME tree topology are determined by polyhedral subdivisions of the spaces of dissimilarity maps

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to study the optimality of the neighbor-joining algorithm. In particular, we investigate and compare the polyhedral subdivisions for n ≤ 8. This requires the measurement of volumes of spherical polytopes in high dimension, which we obtain using a combination of Monte Carlo methods and polyhedral algorithms. Our results include a demonstration that highly unrelated trees can be co-optimal in BME reconstruction, and that NJ regions are not convex. We obtain the l
2 radius for neighbor-joining for n = 5 and we conjecture that the ability of the neighbor-joining algorithm to recover the BME tree depends on the diameter of the BME tree.
UV laser mediated cell selective destruction by confocal microscopy
Authors: Soustelle Laurent , Aigouy Benoît , Asensio Marie-Laure , Giangrande Angela
Published: April 2008

Analysis of cell-cell interactions, cell function and cell lineages greatly benefits selective destruction techniques, which, at present, rely on dedicated, high energy, pulsed lasers and are limited to cells that are detectable by conventional microscopy. We present here a high resolution/sensitivity technique based on confocal microscopy and relying on commonly used UV lasers. Coupling this technique with time-lapse enables the destruction and following of any cell(s) in any pattern(s) in living animals as well as in cell culture systems.
IQ tests as aids to diagnosis and management in early
schizophrenia
Authors: Harrison-Read Phil
Published: April 2008

Intellectual and other more specific neurocognitive impairments in
schizophrenia are important for understanding the aetiology of the condition
and its likely outcome. However, these impairments are not usually
considered important for supporting a diagnosis in suspected early
schizophrenia. IQ testing is widely available and probably acceptable to
most people likely to be experiencing the early stages of psychosis and who
might be unable or unwilling to disclose details of their history and mental
state or to cooperate with more comprehensive neuropsychological assessment.
Although in general IQ tests have only limited diagnostic value in
schizophrenia, the finding of a substantial decline in IQ score from the
estimated premorbid level may be helpful in supporting a provisional
diagnosis of early schizophrenia in cases without organic signs in which the
clinical picture is unclear or incomplete. More important, the results of IQ
tests may contribute to a better understanding of patients' impairments and
assist clinical management in a number of ways, as illustrated here by three
fictional case studies.
Birth weight of infants after maternal exposure to typical and
atypical antipsychotics: Prospective comparison study
Authors: Newham James J. , Thomas Simon H. , MacRitchie Karine , McElhatton Patricia R. , McAllister-Williams R. Hamish
Published: April 2008

Background

The effects of in utero exposure to atypical
antipsychotics on infant birth weight are unknown.

Aims

To determine whether atypical and typical antipsychotics differ in their
effects on birth weight after maternal exposure during pregnancy.

Method

Prospective data on gestational age and birth weight collected by the
National Teratology Information Service for infants exposed to typical
(n=45) and atypical (n=25)
antipsychotics was compared with data for a reference group of infants
(n=38).

Results

Infants exposed to atypical antipsychotics had a significantly higher
incidence of large for gestational age (LGA) than both comparison groups
and a mean birth weight significantly heavier than those exposed to
typical antipsychotics. In contrast those exposed to typical
antipsychotics had a significantly lower mean birth weight and a higher
incidence of small for gestational age infants than the reference
group.

Conclusions

In utero exposure to atypical antipsychotic drugs may
increase infant birth weight and risk of LGA.
Prescribing in pregnancy
Authors: Paton Carol
Published: April 2008

Psychotropic drugs reduce morbidity and mortality related to maternal mental illness but may also cause harm to the foetus, the nature and magnitude of which is not completely understood. Up-to-date information should be shared as fully as possible with the pregnant woman and a treatment plan agreed jointly.
A development programme for newly appointed consultants
Authors: Spurgeon Peter , Vassilas Christopher A. , Flanagan Hugh
Published: April 2008

We developed a programme to help newly appointed consultants cope better with the difficulties they may encounter in their new role. The course was run in a large mental health trust which had been formed by the merger of two trusts 3 years before, as there had been some concerns there about the newly appointed consultants floundering when it came to understanding how the trust and the National Health Service (NHS) operated.
Nonenzymatically Glycated Lipoprotein ApoA‐I in Plasma of Diabetic and Nephropathic Patients
Authors: Lapolla Annunziata , Brioschi Maura , Banfi Cristina , Tremoli Elena , Cosma Chiara , Bonfante Luciana , Cristoni Simone , Seraglia Roberta , Traldi Pietro
Published: April 2008

ApoA‐I, which constitutes 70% of the apolipoprotein content of high‐density lipoproteins, acts as an acceptor for the transfer of phospholipids and free cholesterol from peripheral tissues and transports cholesterol in the liver and other tissue for excretion and steroidogenesis. In order to verify its possible structural alteration in pathological states, plasma samples from healthy, diabetic, and nephropathic subjects have been analyzed by two‐dimensional gel electrophoresis. By this approach, clear differences among the three classes of subjects become evident and, in the case of diabetic and nephropathic patients, intense spots are present. The matrix‐assisted laser desorption/ionization mass spectrometry analysis of their digestion products shows that an overexpression of unglycated and glycated ApoA‐I is present in both pathological states, reasonably affecting the efficiency in cholesterol transport.
Model Studies on Protein Glycation
Authors: Schwarzenbolz Uwe , Mende Susann , Henle Thomas
Published: April 2008

Mixtures of Nα‐hippurylarginin, Nα‐hippuryllysine, and glyoxal were incubated in the absence and presence of Nα‐acetylcysteine in order to assess the individual reactivity of these nucleophilic amino acid residues. The incubations were performed under atmospheric and high hydrostatic pressure (400 MPa), and, at the same time, β‐casein was reacted with glyoxal. The results showed that arginine is the main partner for glyoxal in the absence of cysteine, whereas a lysine derivatization was not apparent. In the presence of cysteine, however, arginine was almost completely protected from the reaction, whereas a noticeable formation of lysine derivatives, mainly carboxymethyllysine, was observed. Based on these findings, a reaction mechanism is proposed to explain the influence of cysteine on the reaction.
Mitigation Strategies to Reduce Acrylamide Formation in Fried Potato Products
Authors: Morales Francisco , Capuano Edoardo , Fogliano Vincenzo
Published: April 2008

Potato products contain high amounts of acrylamide, which sometimes exceeds the concentration of 1 mg/L. However, many strategies for acrylamide reduction in potato products are possible. In this work, the different approaches for reducing acrylamide formation have been reviewed, keeping in mind that in the application of strategies for acrylamide formation, the main criteria to be maintained are the overall organoleptic and nutritional qualities of the final product.
Advanced Glycation End Product Homeostasis
Authors: Vlassara Helen , Uribarri Jaime , Cai Weijing , Striker Gary
Published: April 2008

Increased oxidative stress (OS) underlies many chronic diseases prevalent in aging. Data in humans confirm the hypothesis that advanced glycation end products (AGEs) and other oxidants derived from the diet may be major contributors to increased OS in normal adults as well as those with diabetes mellitus or kidney failure. Mice fed a diet with a lowered (approximately 50%) content of AGEs or a typical calorie‐restricted (CR) diet, accumulated a smaller amount of AGEs, maintained normal levels of AGE receptor‐1 (AGER1), and did not have increased oxidant stress or cardiac or kidney fibrosis with aging. However, the findings in mice fed a CR diet with an increased content of AGEs resembled those in mice fed a nonrestricted diet that had the usual higher content of AGEs. Thus, there was an inverse correlation between the dietary AGE content, the AGER1 to receptor for AGE (RAGE) ratio, OS, organ damage, and life span. In both humans and mice, there was an inverse correlation between the AGER1 to RAGE ratio and the levels of OS.
A verapamil-sensitive chloroquine-associated H+ leak from the digestive vacuole in chloroquine-resistant malaria parasites
Authors: Lehane Adele M. , Hayward Rhys , Saliba Kevin J. , Kirk Kiaran
Published: April 2008

Chloroquine resistance in the malaria parasite Plasmodium falciparum has made malaria increasingly difficult to control. Chloroquine-resistant parasites accumulate less chloroquine than their chloroquine-sensitive counterparts; however, the mechanism underlying this remains unclear. The primary site of accumulation and antimalarial action of chloroquine is the internal acidic digestive vacuole of the parasite, the acidity of which is maintained by inwardly-directed H+ pumps, working against the (outward) leak of H+. In this study we have investigated the leak of H+ from the digestive vacuole of the parasite by monitoring the alkalinisation of the vacuole following inhibition of the H+-pumping V-type ATPase by concanamycin A. The rates of alkalinisation observed in three chloroquine-resistant strains were two- to fourfold higher than those measured in three chloroquine-sensitive strains. On addition of chloroquine there was a dramatic increase in the rate of alkalinisation in the chloroquine-resistant strains, whereas chloroquine caused the rate of alkalinisation to decrease in the chloroquine-sensitive strains. The chloroquine-associated increase in the rate of alkalinisation seen in chloroquine-resistant parasites was inhibited by the chloroquine-resistance reversal agent verapamil. The data are consistent with the hypothesis that in chloroquine-resistant parasites chloroquine effluxes from the digestive vacuole, in association with H+, via a verapamil-sensitive pathway.
Proximity-dependent and proximity-independenttrans-splicing in mammalian cells
Authors: Viles Kristi D. , Sullenger Bruce A.
Published: April 2008

Most human pre-mRNAs arecis-spliced, removing introns and joining flanking exons of the same RNA molecule. However, splicing of exons present on separate pre-mRNA molecules can also occur. Thistrans-splicing reaction can be exploited by pre-trans-splicing molecules (PTMs), which are incapable ofcis-splicing. PTM-mediatedtrans-splicing has been utilized to repair mutant RNAs as a novel approach to gene therapy. Herein we explore how the site of PTM expression influencestrans-splicing activity. We stably inserted a PTM expression cassette into the genome of HEK293 cells, generating clonal lines with single, unique insertion sites. We analyzedtrans-splicing to the gene where the PTM was integrated, as well as genes neighboring these loci. We observed some pre-mRNAs only serve as substrates fortrans-splicing when they are expressed in immediate proximity to the PTM expression site. The need for PTMs to be in close proximity with pre-mRNAs totrans-splice with them is consistent with the observation that pre-mRNAcis-splicing occurs cotranscriptionally. Interestingly, we identified several cellular pre-mRNAs in one localized area that serve astrans-splicing substrates irrespective of the PTM expression site. Thus, we find multiple cellular pre-mRNAs require PTM expression in close proximity totrans-splice while others do not.
Analysis of genomic tRNA sets from Bacteria, Archaea, and Eukarya points to anticodon–codon hydrogen bonds as a major determinant of tRNA compositional variations
Authors: Targanski Ilia , Cherkasova Vera
Published: April 2008

Analysis of 100 complete sets of the cytoplasmic elongator tRNA genes from Bacteria, Archaea, and Eukarya pointed to correspondences between types of anticodon and composition of the rest of the tRNA body. The number of the hydrogen bonds formed between the complementary nucleotides in the anticodon–codon duplex appeared as a major quantitative parameter determining covariations in all three domains of life. Our analysis has supported and advanced the “extended anticodon” concept that is based on the argument that the decoding performance of the anticodon is enhanced by selection of a matching anticodon stem–loop sequence, as reported by Yarus in 1982. In addition to the anticodon stem–loop, we have found covariations between the anticodon nucleotides and the composition of the distant regions of their respective tRNAs that include dihydrouridine (D) and thymidyl (T) stem–loops. The majority of the covariable tRNA positions were found at the regions with the increased dynamic potential—such as stem–loop and stem–stem junctions. The consistent occurrences of the covariations on the multigenomic level suggest that the number and pattern of the hydrogen bonds in the anticodon–codon duplex constitute a major factor in the course of translation that is reflected in the fine-tuning of the tRNA composition and structure.
The RNase E/G-type endoribonuclease of higher plants is located in the chloroplast and cleaves RNA similarly to the E. coli enzyme
Authors: Schein Aleks , Sheffy-Levin Sharon , Glaser Fabian , Schuster Gadi
Published: April 2008

RNase E is an endoribonuclease that has been studied primarily in Escherichia coli, where it is prominently involved in the processing and degradation of RNA. Homologs of bacterial RNase E are encoded in the nuclear genome of higher plants. RNA degradation in the chloroplast, an organelle that originated from a prokaryote similar to cyanobacteria, occurs via the polyadenylation-assisted degradation pathway. In E. coli, this process is probably initiated with the removal of 5′-end phosphates followed by endonucleolytic cleavage by RNase E. The plant homolog has been proposed to function in a similar way in the chloroplast. Here we show that RNase E of Arabidopsis is located in the soluble fraction of the chloroplast as a high molecular weight complex. In order to characterize its endonucleolytic activity, Arabidopsis RNase E was expressed in bacteria and analyzed. Similar to its E. coli counterpart, the endonucleolytic activity of the Arabidopsis enzyme depends on the number of phosphates at the 5′ end, is inhibited by structured RNA, and preferentially cleaves A/U-rich sequences. The enzyme forms an oligomeric complex of ∼680 kDa. The chloroplast localization and the similarity in the two enzymes' characteristics suggest that plant RNase E participates in the initial endonucleolytic cleavage of the polyadenylation-stimulated RNA degradation process in the chloroplast, perhaps in collaboration with the two other chloroplast endonucleases, RNase J and CSP41.
A conserved element that stabilizes the group II intron active site
Authors: Fedorova Olga , Pyle Anna Marie
Published: April 2008

The internal loop at the base of domain 3 (D3) is one of the most conserved and catalytically important elements of a group II intron. However, the location and molecular nature of its tertiary interaction partners has remained unknown. By employing a combination of site-directed photo-cross-linking and nucleotide analog interference suppression (NAIS), we show that the domain 3 internal loop (D3IL) interacts with the ε-ε′ duplex, which is an active-site element located near the 5′-splice site in D1. Our data also suggest that the D3IL may interact with the bulge of D5, which is a critical active site component. The results of this and other recent studies indicate that the D3IL participates in a complex network of tertiary interactions involving ε-ε′, the bulge of D5 and J23, and that it helps to optimize active site architecture by supporting interactions among these catalytic motifs. Our results are consistent with the role of D3 as a catalytic effector that enhances intron reactivity through active site stabilization.
Organization and transcriptional output of a novel mRNA-like piRNA gene (mpiR) located on mouse chromosome 10
Authors: Kim Minjung , Patel Bhavita , Schroeder Kourtney E. , Raza Abbas , Dejong Jeff
Published: April 2008

This letter describes the architecture and transcriptional output of a novel noncoding RNA gene in mouse and rat. The mRNA-like piRNA (mpiR) gene, lies between the Perp and KIAA1244 genes on mouse chromosome 10 and rat chromosome 1. In mouse, the mpiR gene is associated with the production of at least 13 different alternatively spliced and polyadenylated transcripts ranging from 500 nt to over 6 kb. Although these transcripts are structurally similar to conventional mRNAs, only short polypeptides are predicted on each of the three possible reading frames. Intron 2 is unique in that it harbors a novel low copy repeat with homology with the 3′-UTR of the lin-28 gene, while Exon 4 contains an unusual cluster of nine sequence modules that are dispersed throughout the mouse genome. The mpiR gene is expressed at low levels in somatic tissues, but is transcriptionally up-regulated in the testis at day 14 post-partum, a time that coincides with the pachytene stage of meiosis I. Bisulfite methylation analysis shows that expression in brain, liver, and testis is correlated with the methylation status of the promoter region. In addition to mRNA-like transcripts, the mpiR gene is also a precursor to testis-specific piRNAs, and these can be detected by both Northern and PCR-based approaches. Remarkably, piRNAs originate from two specific regions of the gene, one corresponding to Intron 2 and the other to Exon 4. Overall, this work provides a picture of a novel, lineage-specific, noncoding RNA gene and describes its processing into both mRNA-like and piRNA products.
The 5e motif of eukaryotic signal recognition particle RNA contains a conserved adenosine for the binding of SRP72
Authors: Iakhiaeva Elena , Wower Jacek , Wower Iwona K. , Zwieb Christian
Published: April 2008

The signal recognition particle (SRP) plays a pivotal role in transporting proteins to cell membranes. In higher eukaryotes, SRP consists of an RNA molecule and six proteins. The largest of the SRP proteins, SRP72, was found previously to bind to the SRP RNA. A fragment of human SRP72 (72c′) bound effectively to human SRP RNA but only weakly to the similar SRP RNA of the archaeon Methanococcus jannaschii. Chimeras between the human and M. jannaschii SRP RNAs were constructed and used as substrates for 72c′. SRP RNA helical section 5e contained the 72c′ binding site. Systematic alteration within 5e revealed that the A240G and A240C changes dramatically reduced the binding of 72c′. Human SRP RNA with a single A240G change was unable to form a complex with full-length human SRP72. Two small RNA fragments, one composed of helical section 5ef, the other of section 5e, competed equally well for the binding of 72c′, demonstrating that no other regions of the SRPR RNA were required. The biochemical data completely agreed with the nucleotide conservation pattern observed across the phylogenetic spectrum. Thus, most eukaryotic SRP RNAs are likely to require for function an adenosine within their 5e motifs. The human 5ef RNA was remarkably resistant to ribonucleolytic attack suggesting that the 240-AUC-242 “loop” and its surrounding nucleotides form a peculiar compact structure recognized only by SRP72.
gRNA/pre-mRNA annealing and RNA chaperone activities of RBP16
Authors: Ammerman Michelle L. , Fisk John C. , Read Laurie K.
Published: April 2008

Editing in trypanosomes involves the addition or deletion of uridines at specific sites to produce translatable mitochondrial mRNAs. RBP16 is an accessory factor from Trypanosoma brucei that affects mitochondrial RNA editing in vivo and also stimulates editing in vitro. We report here experiments aimed at elucidating the biochemical activities of RBP16 involved in modulating RNA editing. In vitro RNA annealing assays demonstrate that RBP16 significantly stimulates the annealing of gRNAs to cognate pre-mRNAs. In addition, RBP16 also facilitates hybridization of partially complementary RNAs unrelated to the editing process. The RNA annealing activity of RBP16 is independent of its high-affinity binding to gRNA oligo(U) tails, consistent with the previously reported in vitro editing stimulatory properties of the protein. In vivo studies expressing recombinant RBP16 in mutant Escherichia coli strains demonstrate that RBP16 is an RNA chaperone and that in addition to RNA annealing activity, it contains RNA unwinding activity. Our data suggest that the mechanism by which RBP16 facilitates RNA editing involves its capacity to modulate RNA secondary structure and promote gRNA/pre-mRNA annealing.
Strategic Capacity Rationing to Induce Early Purchases
Authors: Liu Qian , van Ryzin Garrett J.
Published: April 2008

Dynamic pricing offers the potential to increase revenues. At the same time, it creates an incentive for customers to strategize over the timing of their purchases. A firm should ideally account for this behavior when making its pricing and stocking decisions. In particular, we investigate whether it is optimal for a firm to create rationing risk by deliberately understocking products. Then, the resulting threat of shortages creates an incentive for customers to purchase early at higher prices. But when does such a strategy make sense? If it is profitable to create shortages, what is the optimal amount of rationing risk to create? We develop a stylized model to study this problem. In our model, customers have heterogeneous valuations for the firm's product and face declining prices over two periods. Customers are assumed to have identical risk preferences and know the price path and fill rate in each period. Via its capacity choice, the firm is able to control the fill rate and, hence, the rationing risk faced by customers. Customers behave strategically and weigh the payoff of immediate purchases against the expected payoff of delaying their purchases. We analyze the capacity choice that maximizes the firm's profits. First, we consider a monopoly market and characterize conditions under which rationing is optimal. We examine how the optimal amount of rationing is affected by the magnitude of price changes over time and the degree of risk aversion among customers. We then analyze an oligopoly version of the model and show that competition reduces the firms' ability to profit from rationing. Indeed, there exists a critical number of firms beyond which a rationing equilibrium cannot be supported.
Does the Standardization Process Matter? A Study of Cost Effectiveness in Hospital Drug Formularies
Authors: Kwon Seok-Woo
Published: April 2008

While research on the cost effectiveness of standardization to date has focused on the impact of different degrees of standardization, it has paid insufficient attention to the process an organization uses to formulate and implement standardized procedures. Drawing on the organizational decision-making literature and procedural fairness literature, this study identifies a number of key process features in standardization and argues that variations in these process features across organizations help account for the varying success of standardization in achieving cost effectiveness. Using hospital drug standardization for coronary artery and pneumonia cases to ground much of the argument, I analyzed inpatient discharge data from Florida, Illinois, New York, and Texas, combined with an original survey of 243 hospital pharmacy directors. The results indicated that an increasing degree of standardization was associated with cost effectiveness when the level of formal objectivity in creating the standardized procedure was high and when there was due process in resolving disputes about the standardized procedure. This finding broadly supports the argument that the cost effectiveness of standardization depends not just on the degree of standardization but also on the process by which the standardized procedures are created and implemented.
Managing Inventory Over a Short Season: Models with Two Procurement Opportunities
Authors: Li Jian , Chand Suresh , Dada Maqbool , Mehta Shailendra
Published: April 2008

Motivated by many recent applications reported in the literature, we examine the impact of a second procurement opportunity on inventory management of products with short selling seasons. In our framework, the first order is placed at the start of the preseason and delivered at the start of the selling season; the second order is placed at or after the start of the selling season for subsequent delivery. Under this framework, the decision maker must make three interrelated choices: the first order quantity, when to place the second order, and the second order quantity. Our focus is on elucidating the optimal policy structure for the three interrelated decisions. By casting our models as sequential decision-making problems, we are able to reduce the optimization problems into sequential and embedded searches for the concerned decision variables that allow us to identify the conditions on the economic parameters and demand distribution to effectively facilitate the search for the optimal solutions.
OM Practice—Balancing Risk and Efficiency at a Major Commercial Bank
Authors: Kekre Sunder , Secomandi Nicola , Sönmez Erkut , West Kenneth
Published: April 2008

Check processing institutions are being forced to downsize their workforce to cut cost and improve the efficiency of their operations as a result of continued growth of electronic payments, a consequence of the increasing popularity of debit/credit cards and use of online banking. For these institutions, these events are making more urgent the decision of how to staff a check-clearing house to trade off efficiency and the expected costs associated with the risks of delayed checks, which include fraud and float costs. In this paper, we discuss how a team of executives at a major commercial bank (CB) and Carnegie Mellon University students and faculty engaged in conducting a model-based study of the CB check-clearing operations. This project culminated in the development of a simulation optimization model to systematically analyze the nature of the highlighted risk efficiency trade-off at CB. The firm used the model recommendations to obtain operations downsizing guidelines for its senior managers during the implementation of a strategic workforce reduction program at their check-clearing house. The managerial insights from the team analysis, and the specific model-based recommendations, enabled CB executives to balance risk and efficiency while planning the reduction of their check-processing workforce.
Scheduling Flexible Servers with Convex Delay Costs in Many-Server Service Systems
Authors: Gurvich Itay , Whitt Ward
Published: April 2008

In a recent paper we introduced the queue-and-idleness ratio (QIR) family of routing rules for many-server service systems with multiple customer classes and server pools. A newly available server serves the customer from the head of the queue of the class (from among those the server is eligible to serve) whose queue length most exceeds a specified proportion of the total queue length. Under fairly general conditions, QIR produces an important state-space collapse as the total arrival rate and the numbers of servers increase in a coordinated way. That state-space collapse was previously used to delicately balance service levels for the different customer classes. In this sequel, we show that a special version of QIR stochastically minimizes convex holding costs in a finite-horizon setting when the service rates are restricted to be pool dependent. Under additional regularity conditions, the special version of QIR reduces to a simple policy: linear costs produce a priority-type rule, in which the least-cost customers are given low priority. Strictly convex costs (plus other regularity conditions) produce a many-server analogue of the generalized-cμ (Gcμ) rule, under which a newly available server selects a customer from the class experiencing the greatest marginal cost at that time.
Investigating the Microstructure of Network Evolution: Alliance Formation in the Mobile Communications Industry
Authors: Rosenkopf Lori , Padula Giovanna
Published: April 2008

Theories of network evolution frequently focus on “network endogeneity,” which stresses predictable, path-dependent evolution rooted in previous network structure. However, theories of technological evolution and innovation remind us that networks may undergo significant change as technological discontinuities exert pressures on existing relationships and firms engage in exploratory search. How can we incorporate sources of change into our theories of network evolution instead of focusing so squarely on sources of inertia? By using recent advances in graph theory, we develop a more flexible theory of network evolution by examining two patterns of partner selection that have the potential to change networks: “shortcut” formation between relatively unconnected partner clusters, and the entry of new firms into the “main component” of incumbent partners. Our findings suggest an important contingency for the endogeneity perspective: structural homophily predicts shortcut formation but not alliance formation within clusters. Furthermore, we demonstrate that the pattern of alliance formation between incumbents and new entrants to the alliance network is driven by a combination of endogenous and exogenous mechanisms. New entrants attach to more prominent incumbents, but they are more likely to attach with an alliance deal that comprises multiple partners. We demonstrate these findings in an industry where systemic technology encourages cooperation and where network entry is prevalent—the mobile communications industry from 1993–2002.
Interorganizational Trust, Governance Choice, and Exchange Performance
Authors: Gulati Ranjay , Nickerson Jack A.
Published: April 2008

This paper looks at when and how preexisting interorganizational trust influences the choice of governance and in turn the performance of exchange relationships. We theorize that preexisting interorganizational trust complements the choice of governance mode (make, ally, or buy) and also promotes substitution effects on governance mode choice while impacting exchange performance. We evaluate hypotheses using a novel three-stage switching regression model and a sample of 222 component-sourcing arrangements of two assemblers in the automobile industry. Analysis of our data broadly supports our hypotheses. High levels of preexisting interorganizational trust increased the probability that a less formal, and thus less costly, mode of governance was chosen over a more formal one. This finding suggests a substitution effect of interorganizational trust on governance mode choice that in turn shapes exchange performance. We also found a complementary effect of trust on performance: Regardless of the governance mode chosen for an exchange, trust enhanced exchange performance. Additional evidence of the complementary effect of trust on performance was that trust somewhat reduced interorganizational conflict.
How Relational and Organizational Identification Converge: Processes and Conditions
Authors: Sluss David M. , Ashforth Blake E.
Published: April 2008

Separate research literatures focus on the individual's identification with relationships, groups, organizations, and other workplace targets. We propose that identification with one referent may converge with or extend to another, thus suggesting the potential for more parsimonious perspectives on identification. We illustrate this argument by examining how the subordinate's identification with the subordinate-manager role relationship (“relational identification”) (RI) may converge with the subordinate's organizational identification (OI). We propose that convergence occurs through cognitive, affective, and behavioral mechanisms, including social influence, anthropomorphization, personalization, affect transfer, and behavioral sensemaking. We also propose that convergence is conditioned by task interdependence (inherent in the role relationship) and prototypicality (of the relational other). We discuss the implications of our convergence model for future research on multiple identifications.
A Core/Periphery Perspective on Individual Creative Performance: Social Networks and Cinematic Achievements in the Hollywood Film Industry
Authors: Cattani Gino , Ferriani Simone
Published: April 2008

The paper advances a relational perspective to studying creativity at the individual level. Building on social network theory and techniques, we examine the role of social networks in shaping individuals' ability to generate a creative outcome. More specifically, we argue that individuals who occupy an intermediate position between the core and the periphery of their social system are in a favorable position to achieve creative results. In addition, the benefits accrued through an individual's intermediate core/periphery position can also be observed at the team level, when the same individual works in a team whose members come from both ends of the core/periphery continuum. We situate the analysis and test our hypotheses within the context of the Hollywood motion picture industry, which we trace over the period 1992–2003. The theoretical implications of the results are discussed.

This work is licensed under a Creative Commons Attribution 4.0 International License. You are free to copy, distribute, transmit and adapt this work, but you must attribute this work as “Organization Science. Copyright © 2017 INFORMS. https://doi.org/10.1287/orsc.1070.0350 , used under a Creative Commons Attribution License: http://creativecommons.org/licenses/by/4.0/ .”
Total ankle replacement
Authors: Wood P. L. R. , Prem H. , Sutton C.
Published: April 2008

We describe the medium-term results of a prospective study of 200 total ankle replacements at a single-centre using the Scandinavian Total Ankle Replacement. A total of 24 ankles (12%) have been revised, 20 by fusion and four by further replacement and 27 patients (33 ankles) have died. All the surviving patients were seen at a minimum of five years after operation. The five-year survival was 93.3% (95% confidence interval (CI) 89.8 to 96.8) and the ten-year survival 80.3% (95% CI 71.0 to 89.6).

Anterior subluxation of the talus, often seen on the lateral radiograph in osteoarthritic ankles, was corrected and, in most instances, the anatomical alignment was restored by total ankle replacement. The orientation of the tibial component, as seen on the lateral radiograph, also affects the position of the talus and if not correct can hold the talus in an abnormal anterior position. Subtalar arthritis may continue to progress after total ankle replacement. Our results are similar to those published previously.
Release of the medial collateral ligament to improve flexion in post-traumatic elbow stiffness
Authors: Ruch D. S. , Shen J. , Chloros G. D. , Krings E. , Papadonikolakis A.
Published: April 2008

Contracture of the collateral ligaments is considered to be an important factor in post-traumatic stiffness of the elbow. We reviewed the results of isolated release of the medial collateral ligament in a series of 14 patients with post-traumatic loss of elbow flexion treated between 1998 and 2002. There were nine women and five men with a mean age of 45 years (17 to 76). They were reviewed at a mean follow-up of 25 months (9 to 48). The operation was performed through a longitudinal posteromedial incision centred over the ulnar nerve. After decompression of the ulnar nerve, release of the medial collateral ligament was done sequentially starting with the posterior bundle and the transverse component of the ligament, with measurement of the arc of movement after each step. If full flexion was not achieved the posterior half of the anterior bundle of the medial collateral ligament was released.

At the latest follow-up, the mean flexion of the elbow improved significantly from 96° (85° to 115°) pre-operatively to 130° (110° to 150°) at final follow-up (p = 0.001). The mean extension improved significantly from 43° (5° to 90°) pre-operatively to 22° (5° to 40°) at final follow-up (p = 0.003). There was a significant improvement in the functional outcome. The mean Broberg and Morrey score increased from a mean of 54 points (29.5 to 85) pre-operatively to 87 points (57 to 99) at final follow-up (p < 0.001). All the patients had normal elbow stability.

Our results indicate that partial surgical release of the medial collateral ligament is associated with improved range of movement of the elbow in patients with post-traumatic stiffness, but was less effective in controlling pain.
Total knee replacement performed with either a mini-midvastus or a standard approach
Authors: Karachalios Th. , Giotikas D. , Roidis N. , Poultsides L. , Bargiotas K. , Malizos K. N.
Published: April 2008

We report the clinical and radiological results of a two- to three-year prospective randomised study which was designed to compare a minimally-invasive technique with a standard technique in total knee replacement and was undertaken between January 2004 and May 2007. The mini-midvastus approach was used on 50 patients (group A) and a standard approach on 50 patients (group B). The mean follow-up in both groups was 23 months (24 to 35).

The functional outcome was better in group A up to nine months after operation, as shown by statistically significant differences in the mean function score, mean total score and the mean Oxford knee score (all, p = 0.05). Patients in group A had statistically significant greater early flexion (p = 0.04) and reached their greatest mean knee flexion of 126.5° (95° to 135°) 21 days after operation. However, at final follow-up there was no significant difference in the mean maximum flexion between the groups (p = 0.08). Technical errors were identified in six patients from group A (12%) on radiological evaluation.

Based on these results, the authors currently use minimally-invasive techniques in total knee replacement in selected cases only.
The functional relevance of neurological recovery after lumbar discectomy
Authors: Mariconda M. , Galasso O. , Secondulfo V. , Cozzolino A. , Milano C.
Published: April 2008

We have studied 180 patients (128 men and 52 women) who had undergone lumbar discectomy at a mean of 25.4 years (20 to 32) after operation. Pre-operatively, most patients (70 patients; 38.9%) had abnormal reflexes and/or muscle weakness in the leg (96 patients; 53.3%). At follow-up 42 patients (60%) with abnormal reflexes pre-operatively had fully recovered and 72 (75%) with pre-operative muscle impairment had normal muscle strength. When we looked at patient-reported outcomes, we found that the Short form-36 summary scores were similar to the aged-matched normative values. No disability or minimum disability on the Oswestry disability index was reported by 136 patients (75.6%), and 162 (90%) were satisfied with their operation. The most important predictors of patients’ self-reported positive outcome were male gender and higher educational level. No association was detected between muscle recovery and outcome.

Most patients who had undergone lumbar discectomy had long-lasting neurological recovery. If the motor deficit persists after operation, patients can still expect a long-term satisfactory outcome, provided that they have relief from pain immediately after surgery.
The long-term outcome of high tibial osteotomy
Authors: Akizuki S. , Shibakawa A. , Takizawa T. , Yamazaki I. , Horiuchi H.
Published: April 2008

We carried out a prospective study of 132 patients (159 knees) who underwent closed-wedge high tibial osteotomy for severe medial compartment osteoarthritis between 1988 and 1997. A total of 94 patients (118 knees) was available for review at a mean of 16.4 years (16 to 20). Seven patients (7.4%) (11 knees) required conversion to total knee replacement. Kaplan-Meier survival was 97.6% (95% confidence interval 95.0 to 100) at ten years and 90.4% (95% confidence interval 84.1 to 96.7) at 15 years. Excellent and good results as assessed by the Hospital for Special Surgery knee score were achieved in 87 knees (73.7%). A pre-operative body mass index > 27.5 kg/m2 and range of movement < 100° were risk factors predicting early failure.

Although our long-term results were satisfactory, strict indications for osteotomy are required if long-term survival is required.
The Effects of Display Code and Its Relation to the Optimal Decision Statistic in Visual Signal Detection
Authors: Montgomery DeMaris A. , Sorkin Robert D.
Published: April 2008

This study examined the effects of display element arrangement on observers' performance in both Yes/No and Four-Alternative-Forced-Choice (4AFC) visual signal detection tasks. Observers were given four independent informational sources whose values were drawn from either a signal or noise distribution, depending on the task and type of trial. The information was displayed graphically in one of six formats constructed from a combination of two factors: 1) whether the display elements were arranged to produce an emergent feature, and 2) whether or not the magnitude of the emergent feature was monotonically related to the optimal decision statistic (for the Yes/No task). Arranging the line graph displays to produce an emergent feature improved Yes/ No performance and impaired 4AFC performance. Due to the highly efficient performance produced by the angular element code, it was not possible to determine whether visual signal detection was affected by the relationship between the emergent feature and the optimal decision statistic.
Effect of Head-Slaved Visual Image Roll on Spatial Situation Awareness
Authors: Adelstein Bernard D. , Ellis Stephen R.
Published: April 2008

We examined whether the inclusion of a third head-slaved “roll” degree of freedom (dof)–in addition to pitch and yaw dofs–to control the orientation of a remotely-viewed or computer-synthesized scene can enhance spatial situation awareness. Six subjects were required to match the position and orientation of stationary target markers on a remote taskboard by manually placing response markers on an identical local taskboard. Subjects could only view the remote taskboard through images transmitted to a head mounted display (HMD) from a motorized pitch-yaw-roll camera platform; they could see neither the local taskboard nor their own limbs. Results show that, while systematic overshoot errors in azimuth judgment occurred regardless of the roll condition, the addition of the roll dof to the platform had no statistically discernible effect on the subjects' ability to match the position ( i.e., azimuth and elevation) of the remote targets. Absence of the roll dof, however, did affect the subjects' judgment of target orientation when their heads were at maximum elevation (pitch) and azimuth (yaw) combinations.
Requirements for Hud Raster Image Modulation in Daylight
Authors: Lloyd Charles J.C. , Reinhart William F.
Published: April 2008

Head-up displays (HUDs) represent the leading candidate display technology for inclusion in an enhanced or synthetic vision system (EVS or SVS) for commercial transport aircraft. One common EVS concept assumes the raster display of raw or processed sensor (radar or IR) data. However, experience with the use of raster rather than stroke display modes has been largely limited to the presentation of images captured by IR sensitive and image-intensified cameras during night flying conditions when the luminance of the forward scene over which the image will be superimposed is much lower than in daytime. The objective of this work is to generate a specification for minimum HUD raster image modulation assuming real-world luminance values typically found in low-visibility, daylight flight. Six Honeywell pilots rated the image quality and utility of flight video as presented through a military-style HUD in a transport cockpit mockup. Flight video came from daylight FLIR and daylight CCD cameras. The luminance of the forward scene against which the HUD image was superimposed was varied among nine levels ranging from 5 fL to 10,000 fL. The results indicate that HUD raster luminance must be approximately 50% external scene luminance to promote good pilot awareness of general terrain. To maintain good utility and visibility of standard, high-contrast runway markings, runway center line, and runway edges, HUD raster luminance must be approximately 15% of the forward scene luminance.
Eye Movements in Search and Target Acquisition
Authors: Birkmire Deborah P. , Karsh Robert , Barnette B. Diane , Pillalamarri Ramakrishna , DiBastiani Samantha
Published: April 2008

The frequency distribution of eye fixations and fixation durations during a search and target acquisition task was examined to determine if the allocation of visual attention was related to target, scene, and/or observer characteristics. Ninety computer-generated scenes simulating infrared imagery and containing different levels of clutter and zero, one, two, or three targets were produced. Targets were embedded in these scenes counterbalancing for range and position. Global and local clutter were measured using both statistical variance and probability of edge metrics. Thirty-three aviators, tankers, and infantry soldiers were shown still video images of the 90 scenes and were instructed to search for targets. Results of multiple regression analyses of global clutter, local clutter, range, number of targets, target dimensions, target complexity, and group membershi on eye fixations and fixation durations are given and discussed in terms of search strategies.
Simulation of Human Visual Search in Cluttered Backgrounds
Authors: Doll Theodore J. , McWhorter Shane W. , Schmieder David E.
Published: April 2008

Work in progress at Georgia Tech to develop a model of human pattern perception, visual search, and detection is reviewed. The model's algorithms are based on research on low-level visual processes. Recent advances in that field have led to the development of computational models of the image processing performed by the visual system from the cornea to the striate cortex. The model also incorporates recent advances from research on visual search. The organization of the model is described, and the results of some preliminary tests are presented.