bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intelligent Versus Random Beavers—an Agent‐Based Approach in Facing the Busy Beaver Problem
Authors: Perrone Alessandro , Ferraris Gianluigi 
Published: May 2004

ABSTRACTSince Tibor Rado in 1962 defined the busy beaver game, several approaches have used computer technology to search for ‘best’ candidates to solve it. In this paper we follow an ‘evolutionary approach’ to solving it using agent‐based techniques. This approach includes techniques to reduce the number of inspected Turing machines and to accelerate simulation of Turing machines using agent‐based techniques; in particular we use the ‘Swarm simulation toolkit’. Our approach uses a variety of learning techniques such as genetic algorithms, classifier systems multiple genetic algorithms and random search to explore the universe of the ‘best solution’ to the game.
Tritrophic interactions and trade‐offs in herbivore fecundity on hybridising host plants
Authors: Cattell Maria V. , Stiling Peter 
Published: May 2004

Abstract. 1. Interspecific plant hybridisation can have important evolutionary consequences for hybridising plants and for the organisms that they interact with on multiple trophic levels. In this study the effects of plant hybridisation on the abundance of herbivores and on the levels of herbivore parasitism were investigated.2.Borrichia frutescens,B. arborescens, and their hybrid (B. × cubana) were censused forAsphondylia borrichiaegalls andPissonotus quadripustulatusplant hoppers in the Florida Keys. Levels of egg parasitism were determined by dissecting parental and hybrid stems and galls for herbivore and parasite eggs and larvae. Stem toughness and gall size are plant‐mediated modes of protection from parasitism and these were also measured. For gall midges, fly size was measured as an estimate of fecundity.3. Field censuses indicated that herbivore abundances varied on hybrid hosts relative to parent plant species and that the different herbivore species exhibited different patterns of abundance.Asphondylia borrichiaegall numbers followed the additive pattern of abundance whileP. quadripustulatusnumbers most closely resembled the dominance pattern.4. Parasitism ofP. quadripustulatuseggs was high onB. frutescensand the hybrids, and low onB. arborescens, which also had significantly tougher stems.Asphondylia borrichiaesuffered the highest levels of parasitism onB. frutescens, the host plant which produced the smallest galls. OnB. arborescens, which produced the largest galls, levels ofA. borrichiaeparasitism were lowest. Both parasitism and gall size were intermediate on the hybrid plants. Galls onB. arborescensand hybrid plants produced significantly smaller flies then those fromB. frutescenssuggesting that, when selecting hosts from among parent species and hybrids, gall flies may face a trade‐off between escape from natural enemies and maximising fecundity.
How Did It Happen?
Authors: Brennan Michael J. 
Published: May 2004

This paper discusses the factors that led up to the stock price bubble of the 1990s. Foremost among these, it is argued, was the conventional view that stocks are the investment of choice for the long‐run investor regardless of their price. This conventional view was based on a misunderstanding of academic theories developed over the past half century. Additional factors were the changing nature of US pensions which placed much more responsibility on the shoulders of the individual investor, and agency problems in investment management and the production of information about firm profitability. Finally there is some evidence that required rates of return were declining during this period. (J.E.L.: G10 and G23).
Patents and R&D as Real Options
Authors: Schwartz Eduardo S. 
Published: May 2004

This article develops and implements a simulation approach to value patents and patent‐protected R&D projects based on the Real Options approach. It takes into account uncertainty in the cost‐to‐completion of the project, uncertainty in the cash flows to be generated from the project, and the possibility of catastrophic events that could put an end to the effort before it is completed. It also allows for the possibility of abandoning the project when costs turn out to be larger than expected or when estimated cash flows turn out to be smaller than anticipated. This abandonment option represents a very substantial part of the project's value when the project is marginal or/and when uncertainty is large. The model presented can be used to evaluate the effects of regulation on the cost of innovation and the amount on innovative output. The main focus of the article is the pharmaceutical industry. The framework, however, applies just as well to other research‐intensive industries such as software or hardware development. (J.E.L.:G31, O22, O32).
Corporate Decisions, Information and Prices: Do Managers Move Prices or Do Prices Move Managers?
Authors: Giammarino Ronald , Heinkel Robert , Hollifield Burton , Li Kai 
Published: May 2004

Seasoned equity offerings involve two significant events: registration followed by the decision to complete the issue or withdraw the registration. We present an empirical analysis of the interaction between seasoned equity issues, insider trading and the incorporation of information in prices around these two events. We find that the manager moves prices through corporate decisions but not personal ones. Specifically, the market reacts to the registration and the registration triggers information acquisition by the market, which is shown to influence the manager's final decision. Trading by managers during this interval does not, however, move prices. (J.E.L.: G14, G23, G32).
Investment, uncertainty and irreversibility
Authors: Khuong Ninh Le , Hermes Niels , Lanjouw Ger 
Published: May 2004

AbstractThis paper investigates the irreversibility of investments and the impact this has on the nature of the relationship between investment and uncertainty. The empirical analysis uses firm‐level data and is based on a survey of 210 rice‐milling firms in the Mekong River Delta in Vietnam, which was carried out during the year 2000. We show that uncertainty reduces investment of rice millers in the presence of irreversibility, as is predicted by the real options approach to investment. We do not find evidence that the negative association between uncertainty and investment is influenced by the degree of irreversibility.
How labile are the egg‐laying preferences of seed beetles?
Authors: Messina Frank J. 
Published: May 2004

Abstract. 1. Previous studies have produced conflicting results with respect to the genetic lability of host preference in the seed beetleCallosobruchus maculatus.2. In this study, replicate lines of an Asian population were kept on an ancestral host (mung bean) or switched to a novel host (cowpea). After 40+ generations, lines were assayed for host preference (in choice tests) and host acceptance (under no‐choice conditions), and were compared to African lines chronically associated with cowpea.3. Host preference diverged in the expected direction. When presented a mixture of cowpeas and mung beans, females from the cowpea lines laid a greater fraction of their eggs on cowpea than did females from the mung bean lines. Preference for cowpea was nearly as strong in the cowpea lines as it was in the cowpea‐adapted African lines.4. In contrast, the experimental host shift did not affect long‐term host acceptance. African females laid more eggs if given cowpeas than if given mung beans, but realised fecundities in the cowpea and mung bean lines were similar on the two hosts. Females from all lines laid more eggs if they were reared on cowpea than on mung bean, but rearing host had no effect on either relative host acceptance or host preference.5. Comparisons with earlier studies suggest that the lability of host preference varies among beetle populations, which precludes generalisation at the species level. Because lines were maintained under no‐choice conditions, modification of host preference probably occurred via a lower acceptance threshold for the novel host, without a concomitant change in the long‐term acceptance of the ancestral host.
Percentage of canals filled in apical cross sections – an in vitro study of seven obturation techniques
Authors: Jarrett I. S. , Marx D. , Covey D. , Karmazin M. , Lavin M. , Gound T. 
Published: May 2004

AbstractAim  To compare the apical density of several obturation techniques when used in palatal roots of extracted maxillary molars.Methodology  Seventy extracted molars were randomly divided into seven groups with 10 teeth each. The palatal root canals were instrumented to size 60 MAF, coated with Kerr's Pulp Canal Sealer, and obturated using one of seven techniques. The palatal roots were separated from the crowns, decalcified, and sectioned horizontally at 2 and 4 mm from the apex. The cross‐sections were photographed through a microscope, the photos were analysed, and the amount of area in the canal that was obturated with gutta‐percha was measured. The means for the 20 sections per group were calculated and the means were compared using mixed analysis of variance test.Results  Simplifill used in accordance with the manufacturer's directions and Thermafil had the greatest mean obturated area, but neither were statistically better than mechanical lateral or warm vertical compaction (WVC; Schilder Technique). Simplifill as recommended and Thermafil were statistically better than cold lateral (P = 0.0210 and 0.0433, respectively), WVC (continuous wave) (P = 0.0006 and 0.0015), and the modified Simplifill group (P = 0.0010 and 0.0012). In addition, mechanical lateral and WVC (Schilder) had statistically more obturated area than WVC (continuous wave) (P = 0.0054 and 0.0073) and modified Simplifill (P = 0.0015 and 0.0016). Cold lateral and WVC (continuous wave) had significantly more obturated area than modified Simplifill (P = 0.0040 and 0.0087).Conclusions  Simplifill as recommended, Thermafil, mechanical lateral and WVC (Schilder) obturation techniques created more complete obturation using gutta‐percha at the 2 and 4 mm levels than cold lateral, WVC (continuous wave), and Simplifill not used as directed.
VirA of Agrobacterium tumefaciens is an intradimer transphosphorylase and can actively block vir gene expression in the absence of phenolic signals
Authors: Brencic Anja , Xia Qi , Winans Stephen C. 
Published: May 2004

SummaryThe VirA–VirG two‐component system regulates the 30‐gene vir regulon in response to host‐released chemical signals. VirA is a homodimeric membrane‐spanning histidine protein kinase. Here, we show that mutations in two essential VirA residues, His‐474 and Gly‐657, can be complemented by the formation of mixed heterodimers, indicating that each subunit of a VirA dimer transphosphorylates the opposite subunit. VirA contains a receiver domain that inhibits kinase activity. We use the forced heterodimer system to show that the two receiver domains of a VirA dimer act independently and that each inhibits the phosphoacceptor subdomain of the opposite subunit. We also demonstrate that merodiploid strains co‐expressing constitutive VirA mutants and wild‐type VirA show levels of vir gene expression far lower than haploid strains expressing just the constitutive alleles. The fact that wild‐type VirA can actively block vir gene expression in the absence of phenolic signals suggests that it might have a phospho‐VirG phosphatase activity. The receiver domain of VirA is essential for this activity, whereas residues H474 and G657 of the kinase domain are not required. Merodiploid strains co‐expressing a constitutive VirA allele and an allele that is kinase inactive but proficient in the inhibitory activity show strongly inducible vir gene expression, indicating that the inhibitory activity is modulated by environmental signals.
The quormone degradation system of Agrobacterium tumefaciens is regulated by starvation signal and stress alarmone (p)ppGpp
Authors: Zhang Hai‐Bao , Wang Chao , Zhang Lian‐Hui 
Published: May 2004

SummaryA unique signal degradation system has recently been discovered in Agrobacterium tumefaciens. Upon entering stationary phase, A. tumefaciens terminates quorum sensing‐dependent Ti‐plasmid conjugation by degradation of acyl homoserine lactone (AHL) quormone via the enzyme AttM (AHL‐lactonase). attM, together with attK and attL, constitute one transcriptional unit subjected to the control of a common promoter. AttJ, the other member of the signal degradation system, is an IclR‐like negative transcriptional factor, which tightly represses the expression of AttM at the early stage of bacterial growth. In this study, we found that this quormone degradation system is activated by either carbon or nitrogen starvation. Quormone degradation was significantly delayed when bacterial culture was supplemented with extra carbon or nitrogen source in the nutrient‐limited minimal medium before the onset of stationary phase. To identify the signalling pathway and regulatory mechanisms that mediate quormone degradation, we constructed a reporter strain A6(attKLM::lacZ) in which the promoterless lacZ was transcriptionally fused to the attKLM promoter. Transposon mutagenesis of strain A6(attKLM::lacZ) led to identification of the relA gene, which encodes the stress alarmone (p)ppGpp synthetase. Tn5 knock‐out of relA abolished the stationary phase‐dependent expression of attM. We concluded that the A. tumefaciens quormone degradation system is coupled to and regulated by the generic (p)ppGpp stress response machinery.
Sed1p and Srl1p are required to compensate for cell wall instability in Saccharomyces cerevisiae mutants defective in multiple GPI‐anchored mannoproteins
Authors: Hagen Ilja , Ecker Margit , Lagorce Arnaud , Francois Jean M. , Sestak Sergej , Rachel Reinhard , Grossmann Guido , Hauser Nicole C. , Hoheisel Jörg D. , Tanner Widmar , Strahl Sabine 
Published: May 2004

SummaryThe covalently linked cell wall protein Ccw12p of Saccharomyces cerevisiae is a GPI‐anchored protein (V. Mrsa et al., 1999, J Bacteriol 181: 3076–3086). Although only 121 amino acids long, the haemagglutinin‐tagged protein released by laminarinase from the cell wall possesses an apparent molecular mass of > 300 kDa. A membrane‐bound form with an apparent molecular mass of 58 kDa is highly O‐ and N‐glycosylated and contains the GPI anchor. With a half‐life of 2 min, the membrane form is transformed to the > 300 kDa form. The deletion mutant ccw12Δ grows slower than the wild type, is highly sensitive to Calcofluor white and contains 2.5 times more chitin. Further, compared with wild‐type yeast, significantly more proteins are released from intact cells when treated with dithiothreitol. Interestingly, these defects become less pronounced when further GPI‐anchored cell wall proteins are deleted. Mutant ΔGPI (simultaneous deletion of CCW12, CCW13/DAN1, CCW14, TIP1 and CWP1) is similar in many respects to wild‐type yeast. To find out how the cell wall is stabilized in mutant ΔGPI, a genome‐wide transcription analysis was performed. Of 159 significantly regulated genes, 14 encode either known or suspected cell wall‐associated proteins. Analysis of genes affected in transcription revealed that SED1 and SRL1 in particular are required to reconstruct cell wall stability in the absence of multiple GPI‐anchored mannoproteins.
Activation of the redox sensor Pap1 by hydrogen peroxide requires modulation of the intracellular oxidant concentration
Authors: Vivancos Ana P. , Castillo Esther A. , Jones Nic , Ayté José , Hidalgo Elena 
Published: May 2004

SummaryThe transcription factor Pap1 and the MAP kinase Sty1 are key regulators of hydrogen peroxide‐induced responses in Schizosaccharomyces pombe. Pap1 can be activated quickly at low, but not high, hydrogen peroxide concentrations. The MAP kinase Sty1 has been reported to participate in Pap1 activation by the oxidant. Here, we provide biochemical and genetic evidence for the in vivo formation of a hydrogen peroxide‐induced disulphide bond in Pap1, which precedes the rapid and reversible nuclear accumulation of the transcription factor. We show that activation of the Sty1 cascade before the oxidative insult, or overexpression of the Sty1‐regulated genes ctt1 (encoding catalase) or gpx1 (encoding glutathione peroxidase), can accelerate Pap1 entry even at high doses of hydrogen peroxide. In fact, the lack of Sty1 impedes Pap1 nuclear localization, but only at high doses of the oxidant. We propose that, whereas low doses of hydrogen peroxide lead directly to Pap1 oxidation‐activation, high concentrations of the oxidant initially activate the Sty1 pathway, with the consequent increase in scavenging enzymes, which in turn helps to decompose the excess of hydrogen peroxide and achieve an appropriate concentration for the subsequent activation of Pap1. Our results also suggest that activation of Sty1 at high doses of hydrogen peroxide may also be required to trigger other antioxidant activities such as those reverting the overoxidation of cysteine residues at the Pap1 pathway.
The major structural components of two cell surface filaments of Porphyromonas gingivalis are matured through lipoprotein precursors
Authors: Shoji Mikio , Naito Mariko , Yukitake Hideharu , Sato Keiko , Sakai Eiko , Ohara Naoya , Nakayama Koji 
Published: May 2004

SummaryBacterial cell surface filaments play significant roles in adherence to and invasion of host cells. They are generated by the chaperone/usher pathway system (class I fimbriae), the type II secretion system (type IV pili) and the nucleation‐dependent polymerization system (Curli filaments) that are categorized by their modes of expression and assembly. In this study, we found that the periodontal pathogen Porphyromonas gingivalis expressed the major structural components of two cell surface filaments (fimbrilin and the 75 kDa protein) that had extremely long prosequences in their primary gene products. N‐terminal amino acid sequencing of the prosequences, treatment of P. gingivalis cells with globomycin, an inhibitor for lipoprotein‐specific signal peptidase, amino acid substitution of the cysteine residue of the prosequence of fimbrilin and [3H]‐palmitic acid labelling implied that fimbrilin and the 75 kDa protein were matured through their lipoprotein precursor forms. Accumulation of precursor forms of fimbrilin and the 75 kDa protein on the cell surface of the gingipain‐null mutant revealed that Arg‐gingipain processed these precursors on the surface to yield their mature forms, which subsequently assembled into the filamentous structures, suggesting that the transport and assembly of the major component proteins appear to be novel.
P–T conditions and kinematics of shear zones from the southern Adelaide Fold–Thrust Belt, South Australia: insights into the dynamics of a deeply eroded orogenic wedge
Authors: YASSAGHI A. , JAMES P. R. , FLÖTTMANN T. , WINSOR C. N. 
Published: May 2004

Mechanisms are examined for the development of shear zones in the external portion of the southern Adelaide Fold–Thrust Belt, based on geometric and kinematic analyses, balanced cross‐sections, microstructure, pressure, and temperature of deformation estimates. Kinematic indicators reveal the zones were overthrust towards the west‐northwest. Shear‐zone quartz‐grain microstructures show mainly intracrystalline deformation and dynamic recrystallisation where there is greater grain dislocation. These features become less well developed in the shear zones closer to the hinterland, than in those on the foreland side. Primary fluid inclusions in deformed quartz veins reveal that average temperatures were in excess of 358°C and indicate an average pressure of about 300 MPa. Microprobe analyses of coexisting biotite–muscovite–quartz–feldspar reveal an average peak metamorphic pressure of 250 ± 100 MPa, compatible with the estimated pressure of 300 MPa from primary fluid inclusions. Modified fluid inclusions, however, suggest an average entrapment pressure of less than 150 MPa, which suggests that they suffered overpressuring during exhumation, implying that the amount of shear‐zone exhumation decreases towards the foreland. Based on this information, an orogenic wedge model is the preferred mechanism for shear‐zone development. The earliest generated and propagated shear zones in the hinterland were buried at greater depth and remained at higher temperatures and pressures before being exhumed. Later shear zones generated closer to the foreland propagated from shallower depths, implying that they experienced lower pressures and temperatures before uplift.
Miocene volcanic seamounts on northern Lord Howe Rise: lithology, age and origin
Authors: EXON N. F. , QUILTY P. G. , LAFOY Y. , CRAWFORD A. J. , AUZENDE J‐M. 
Published: May 2004

Multibeam sonar swath‐mapping has revealed small submarine volcanic cones on the northeastern Lord Howe Rise, a submerged ribbon continent. Two such cones, aligned north‐northwest and 120 km apart, were dredged at 23–24°S. Water depth is about 1150 m nearby: the southern cone rises to 750 m and the northern to 900 m. Volcanic rocks dredged from the cones are predominantly highly altered hyaloclastites with minor basalt. The clasts are mostly intensely altered vesicular brownish glass with lesser basalt, set in zeolitic, clayey, micritic, or ferruginous cement. Lavas and hyaloclastites contain altered phenocrysts of olivine and plagioclase, and fresh clinopyroxene. The latter have compositions between acmite and Ti‐augite, matching clinopyroxene phenocrysts in undersaturated intraplate basanitic mafic lavas. Interbedded micrites in the volcaniclastics represent calcareous ooze that was deposited with (or later than) the volcanic pile. Foraminifers indicate that the micrite is dominantly Early Miocene (ca 16 Ma), and that the ooze was deposited in cool water. Upper Miocene to Pliocene micrites, presumed to be later infillings, all contain warm‐water forms. This evidence strongly suggests that both cones formed in pelagic depths in the Early Miocene. Ferromanganese crusts from the two cones are up to 7 cm thick and similar physically, but different chemically. The average growth rate is 4 mm/106 y. Copper, nickel, and cobalt content are relatively high in the north, but copper does not exceed 0.08 wt%, nickel 0.65%, and cobalt 0.25%. The Mn:Fe ratio is high in the south (average 13.7) suggesting strong hydrothermal influence. Such small volcanic cones related to intraplate hot‐spot‐type volcanism may occur in extensive fields on the Lord Howe Rise, like those off southern Tasmania. On the Lord Howe Rise, the known small volcanic cones coincide with broad gravity highs in areas of shallow continental basement. The highs are aligned parallel to the Lord Howe Rise margins, and it is probable that the Miocene volcanism is related to jostling on older faults. Other fields of small volcanic seamounts may occur on the Lord Howe Rise on such fractured gravity highs.