bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrastructure in Developing and Transition Countries: Risk and Protection
Authors: Freeman Paul K. , Ch. Pflug Georg
Published: May 2003

This article examines two possible strategies for financing post‐disaster infrastructure rehabilitation in developing and transition countries: relying on ex ante financing instruments (including insurance, catastrophe bonds, and other risk‐transfer instruments) and ex post borrowing or credit. Insurance and other ex ante instruments will increase a country's stability, especially if the government authorities have a difficult time borrowing or otherwise raising funds after a major disaster; however, these instruments have an opportunity cost and can reduce the country's economic growth potential. The cost‐benefit tradeoff is therefore one between economic growth through infrastructure investment and added solvency and stability for the economy. This article develops a model to illustrate this tradeoff. The model, which views the infrastructure of a developing or transition country as a nondiversifiable portfolio that generates returns, can provide a basis for evaluating alternative financing options depending on the country's objectives in terms of growth, solvency, and stability.
Sovereign Cat Bonds and Infrastructure Project Financing
Authors: Croson David , Richter Andreas
Published: May 2003

We examine the opportunities for using catastrophe‐linked securities (or equivalent forms of nondebt contingent capital) to reduce the total costs of funding infrastructure projects in emerging economies. Our objective is to elaborate on methods to reduce the necessity for unanticipated (emergency) project funding immediately after a natural disaster. We also place the existing explanations of sovereign‐level contingent capital into a catastrophic risk management framework. In doing so, we address the following questions. (1) Why might catastrophe‐linked securities be useful to a sovereign nation, over and above their usefulness for insurers and reinsurers? (2) Why are such financial instruments ideally suited for protecting infrastructure projects in emerging economies, under third‐party sponsorship, from low‐probability, high‐consequence events that occur as a result of natural disasters? (3) How can the willingness to pay of a sovereign government in an emerging economy (or its external project sponsor), who values timely completion of infrastructure projects, for such instruments be calculated? To supplement our treatment of these questions, we use a multilayer spreadsheet‐based model (in Microsoft Excel format) to calculate the overall cost reductions possible through the judicious use of catastrophe‐based financial tools. We also report on numerical comparative statics on the value of contingent‐capital financing to avoid project disruption based on varying costs of capital, probability and consequences of disasters, the feasibility of strategies for mid‐stage project abandonment, and the timing of capital commitments to the infrastructure investment. We use these results to identify high‐priority applications of catastrophe‐linked securities so that maximal protection can be realized if the total number of catastrophe instruments is initially limited. The article concludes with potential extensions to our model and opportunities for future research.
The Financial Management of Catastrophic Flood Risks in Emerging‐Economy Countries
Authors: Kunreuther Howard C. , Linnerooth‐Bayer Joanne
Published: May 2003

This article examines the potential of pre‐ and post‐disaster instruments for funding disaster response and recovery and for creating incentives for flood loss mitigation in countries with emerging or transition economies. As a concrete case, we discuss the disaster recovery arrangements following the 1997 flood disaster in Poland. We examine the advantages and limitations of hedging instruments, which are instruments for transferring the risk to investors either through insurance or capital market‐based securities. We compare these mechanisms with financing instruments, whereby the government sets aside funds prior to a disaster or taps its own funding sources after the event occurs. We show how hedging instruments can be designed to create incentives for the mitigation of damage to public infrastructure using the flood proofing of a water‐treatment plant on the hypothetical Topping River as an illustrative example. We conclude that hedging instruments can be an attractive alternative to financing instruments that have been traditionally used in the poorer, emerging‐economy countries to fund disaster recovery. Since very poor countries are likely to have difficulty paying the price of protection prior to a disaster, we suggest that international lending institutions consider innovations for subsidizing these payments.
An Application of the Holistochastic Human Exposure Methodology to Naturally Occurring Arsenic in Bangladesh Drinking Water
Authors: Serre M. L. , Kolovos A. , Christakos G. , Modis K.
Published: May 2003

The occurrence of arsenic in drinking water is an issue of considerable interest. In the case of Bangladesh, arsenic concentrations have been closely monitored since the early 1990s through an extensive sampling network. The focus of the present work is methodological. In particular, we propose the application of a holistochastic framework of human exposure to study lifetime population damage due to arsenic exposure across Bangladesh. The Bayesian Maximum Entropy theory is an important component of this framework, which possesses solid theoretical foundations and offers powerful tools to assimilate a variety of knowledge bases (physical, epidemiologic, toxicokinetic, demographic, etc.) and uncertainty sources (soft data, measurement errors, etc.). The holistochastic exposure approach leads to physically meaningful and informative spatial maps of arsenic distribution in Bangladesh drinking water. Global indicators of the adverse health effects on the population are generated, and valuable insight is gained by blending information from different scientific disciplines. The numerical results indicate an increased lifetime bladder cancer probability for the Bangladesh population due to arsenic. The health effect estimates obtained and the associated uncertainty assessments are valuable tools for a broad spectrum of end‐users.
How New Product Introductions Affect Sales Management Strategy: The Impact of Type of “Newness” of the New Product
Authors: Micheal Kamel , Rochford Linda , Wotruba Thomas R.
Published: May 2003

How do firms adjust sales management strategy for new product launch? Does sales management strategy change more radically for different types of new products such as new‐to‐the‐world products versus product revisions? Because firms introducing a new product rely considerably on their sales force in the product launch effort, the types and degree of changes made in managing the selling effort are important issues. Past studies have demonstrated that firms make substantial adjustments in their sales management strategy when they introduce a new product. This study expands on previous investigations by examining whether sales management strategy changes are conditioned by the type of newness of the new product to the market and to the firm.

Australian sales managers were asked to respond to a mail questionnaire concerning pre‐ and post‐new product launch sales management activities. Three groups of firms were compared: (1) those with new‐to‐the‐market and new‐to‐the‐firm products (i.e., new‐to‐the‐world products); (2) those with products new to the firm but not new to the market; and (3) those with products that are revisions to the firm and not new to the market. The study finds that firms do not make the most adjustments for products with the greatest degree of market newness—the new‐to‐the‐world types of products—except in the sales management strategy categories of compensation and supervision. In the other sales management strategy categories defined for study—organization, training, quotas and goals, and sales support as well as for all categories in the aggregate—sales management strategy changes were greatest in incidence, as measured both by the percent of firms making changes and the average number of changes per firm, when the new product was new to the firm but not new to the market.

These results suggest that, because different types of new products face different competitive environments, there may be greater incentive for a not‐new‐to‐the‐market new‐to‐the‐firm product to make changes in sales strategy. Uncertainties about market size and customer location with new‐to‐the‐world products may limit the understanding of what changes to make in the strategy categories of quotas and territories. Similarly, uncertainties about product use and customer acceptance of new‐to‐the‐world products may limit the development of training and sales support materials by these firms. Instead, these firms may rely more on compensation and supervision to direct sales efforts for new‐to‐the‐world products. However, observing the market experience and performance of the first‐to‐market product can benefit firms launching a not‐new‐to‐market and new‐to‐the‐firm product, allowing them to rely more on strategy changes in training, sales support materials, organizational adjustments such as redeployments, and quotas.
Commercial Innovations from Consulting Engineering Firms: An Empirical Exploration of a Novel Source of New Product Ideas
Authors: Alam Ian
Published: May 2003

Industrial firms interact with many outside organizations such as the customers, suppliers, competitors, and universities to obtain input for their new product development (NPD) programs. The importance of interfirm interactions is reflected in a large number of interdisciplinary studies reported in a wide variety of literature bases. As a result, several sources of new product ideas have been investigated in the extant literature. Yet given the growing complexity and risks in new product development, there seems to be a need for managers to obtain input from new and unutilized sources. Apparently, one source that industry has not tapped adequately for its NPD efforts is the consulting engineering firms (CEFs).

To fill the aforementioned gap in the literature, this article explores the roles and suitability of CEFs in new product development by conducting a rigorous in‐depth case research of new product idea generation in a large Australian firm manufacturing a variety of industrial products. To generate ideas for the sponsoring firm, longitudinal field interviews with 64 managers and engineers from 32 large CEFs were conducted over a one‐and‐one‐half year period. The findings of the field interviews were combined with the documentary evidences and the archival data. This longitudinal data collection enabled the author to generate new product ideas over real time and to gain access to the information that otherwise might have been difficult to obtain.

The results suggest that CEFs are a rich source of new product ideas of potential commercial value. However, industry is making little use of CEFs, which underscores the need for industrial firms to collaborate and to establish an effective idea transfer relationship with them. Moreover, the services of CEFs are not restricted to idea generation but can stretch across the entire NPD process. These findings of the study encourage product managers to conceptualize NPD as a highly synergistic mutually interdependent process between CEFs and industrial firms rather than simply an arm's‐length consulting transactions. Given the dearth of research on idea generation with CEFs, this study highlights the findings that are novel and that go beyond the techniques of new product idea generation established in the extant literature.
A Model of Supplier Integration into New Product Development*
Authors: Petersen Kenneth J. , Handfield Robert B. , Ragatz Gary L.
Published: May 2003

In many industries, firms are looking for ways to cut concept‐to‐customer development time, to improve quality, and to reduce the cost of new products. One approach shown to be successful in Japanese organizations involves the integration of material suppliers early in the new product development cycle. This involvement may range from simple consultation with suppliers on design ideas to making suppliers fully responsible for the design of components or systems they will supply.

While prior research shows the benefit of using this approach, execution remains a problem. The processes for identifying and integrating suppliers into the new product development (NPD) process in North American organizations are not understood well. This problem is compounded by the fact that design team members often are reluctant to listen to the technology and cost ideas made by suppliers in new product development efforts. We suggest a model of the key activities required for successful supplier integration into NPD projects, based on case studies with 17 Japanese and American manufacturing organizations. The model is validated using data from a survey of purchasing executives in global corporations with at least one successful and one unsuccessful supplier integration experience. The results suggest that (1) increased knowledge of a supplier is more likely to result in greater information sharing and involvement of the supplier in the product development process; (2) sharing of technology information results in higher levels of supplier involvement and improved outcomes; (3) supplier involvement on teams generally results in a higher achievement of NPD team goals; (4) in cases when technology uncertainty is present, suppliers and buyers are more likely to share information on NPD teams; and (5) the problems associated with technology uncertainty can be mitigated by greater use of technology sharing and direct supplier participation on new product development teams. A supplier's participation as a true member of a new product development team seems to result in the highest level of benefits, especially in cases when a technology is in its formative stages.
The application of smart structures toward feedback suppression in amplified acoustic guitars
Authors: Griffin Steve , Lane Steven A. , Clark Robert L.
Published: May 2003

Smart structures technology can be applied to amplified acoustic guitars to prevent instability resulting from acoustic feedback. This work presents a coupled model of the guitar dynamics and the acoustic feedback mechanism, and explains how a simple control loop using a piezoelectric ceramic actuator can be used to reduce the effects of acoustic feedback. In addition to model simulations, experimental results using a real system and a simple controller are presented. The results show that a significantly higher (7 dB) guitar output can be achieved before instability, without detrimentally affecting the amplified and unamplified guitar response.
Optimization and implementation of piezoelectric radiators using the genetic algorithm
Authors: Bai Mingsian R. , Huang Chinghong
Published: May 2003

Very thin and small (45 mm×35 mm×0.35 mm) piezoelectric radiators have been developed in this research. The system is modeled by using the energy method in conjunction with the assumed-modes method. Electrical system, mechanical system, and acoustic loading have all been accounted for during the modeling stage. On the basis of the simulation model, the genetic algorithm (GA) is employed to optimize the overall configurations for a low resonance frequency and a large gain. The resulting designs are then implemented and evaluated experimentally. Performance indices for the experimental evaluation include the frequency response, the directional response, the sensitivity, and the efficiency. It is found in the experimental results that the piezoelectric radiators are able to produce comparable acoustical output with significantly less electrical input than the voice-coil panel speakers.
Comment on “Multiple scattering in a reflecting cavity: Application to fish counting in a tank” [J. Acoust. Soc. Am. 109, 2587–2597 (2001)] (L)
Authors: Ye Zhen , Chu Dezhang
Published: May 2003

This paper presents a comment on the recent work on fish counting in a tank [J. Acoust. Soc. Am. 109, 2587–2597 (2001)]. It is pointed out that there are ambiguities with the counting method.
Perceptual weights in auditory level discrimination
Authors: Kortekaas Reinier , Buus Søren , Florentine Mary
Published: May 2003

Perceptual weights in level discrimination (also called intensity discrimination) were determined for 3-, 7-, 15-, and 24-component tone complexes with flat spectral envelopes using a correlational paradigm. Each frequency component was randomly and independently perturbed in level on each presentation. For the target interval, frequency-component levels were additionally increased by the level increment to be detected, ΔL [=20 log10((p+Δp)/p), where p is pressure]. Weights were calculated from the across-trial correlation between the level perturbations for each frequency component and the interval chosen by the listener. Two conditions were investigated: (1) ΔL was equal across frequency components, and (2) ΔL increased progressively across frequency components. For both conditions, data for four listeners usually showed the greatest weight for the highest frequency component. The two-to-four highest frequency components generally were most important for level discrimination. The effect of increasing ΔL progressively with frequency was small and inconsistent. Additional measurements showed that flanking noise maskers designed to mask spread of excitation caused only small and generally unsystematic changes to the weights. Overall, these results indicate that listeners combine information across a wide range of auditory channels to arrive at a decision for level discrimination, but the weighting of channels appears to be suboptimal.
A comparison of psychophysical procedures for level-discrimination thresholds
Authors: Marvit Peter , Florentine Mary , Buus Søren
Published: May 2003

Five different psychophysical procedures were used to measure level-discrimination (also called intensity discrimination) thresholds for 1-kHz tones at two levels (30 and 90 dB SPL) and two durations (10 and 500 ms). The procedures were the classic transformed up–down staircase method with a two-alternative forced-choice (2AFC) paradigm (UPD), 15- and 50-trial implementations of the method of maximum likelihood (MML) with a cued yes–no paradigm, and 18-trial implementations of ZEST using both cued yes–no and 2AFC paradigms. Results obtained from nine normal listeners show that estimates of level-discrimination thresholds for the four conditions are similar across all five procedures when different points of convergence are accounted for. The variance of threshold estimates within listener and condition was smallest for UPD, largest for the MML with 15 trials, and statistically indistinguishable among the others. The sweat factors ranged from 5.5 for MML with 50 trials to about 1.4 for UPD and ZEST. Simulations show that ideal performance of procedures may be far from real-life experience and that these deviations are likely to depend on complex interactions between listener behavior and parameter choices used for implementing the procedures. Therefore, empirical verification is important for judging the effectiveness of psychophysical procedures.
On the use of higher-order azimuthal schemes in 3-D PE modeling
Authors: Sturm Frédéric , Fawcett John A.
Published: May 2003

In this paper, the issue of using higher-order finite difference schemes to handle the azimuthal derivative term in a three-dimensional parabolic equation based model is addressed. The three-dimensional penetrable wedge benchmark problem is chosen to illustrate the accuracy and efficiency of the proposed schemes. Both point source and modal initializations of the pressure field are considered. For each higher-order finite difference scheme used in azimuth, the convergence of the numerical solution with respect to the azimuth is investigated and the CPU times are given. Some comparisons with solutions obtained from another 3-D model [J. A. Fawcett, J. Acoust. Soc. Am. 93, 2627–2632 (1993)] are presented. The numerical simulations show that the use of a higher-order scheme in azimuth allows one to reduce the required number of points in the azimuthal direction while still obtaining accurate solutions. The higher-order schemes have approximately the same efficiency as a FFT-based approach (in fact, may outperform it slightly); however, the finite difference approach has the advantage that it may be more flexible than the FFT approach for various PE approximations.
Electron Transport in Molecular Wire Junctions
Authors: Nitzan Abraham , Ratner Mark A.
Published: May 2003

Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes. In such junctions, the connection between the molecule and the electrodes greatly affects the current-voltage characteristics. Despite several experimental and theoretical advances, including the understanding of simple systems, there is still limited correspondence between experimental and theoretical studies of these systems.
Disruption of the Epithelial Apical-Junctional Complex by
Helicobacter pylori
CagA
Authors: Amieva Manuel R. , Vogelmann Roger , Covacci Antonello , Tompkins Lucy S. , Nelson W. James , Falkow Stanley
Published: May 2003

Helicobacter pylori
translocates the protein CagA into gastric epithelial cells and has been linked to peptic ulcer disease and gastric carcinoma. We show that injected CagA associates with the epithelial tight-junction scaffolding protein ZO-1 and the transmembrane protein junctional adhesion molecule, causing an ectopic assembly of tight-junction components at sites of bacterial attachment, and altering the composition and function of the apical-junctional complex. Long-term CagA delivery to polarized epithelia caused a disruption of the epithelial barrier function and dysplastic alterations in epithelial cell morphology. CagA appears to target
H. pylori
to host cell intercellular junctions and to disrupt junction-mediated functions.
Real-Time Monitoring of Growing Nanoparticles
Authors: Renaud Gilles , Lazzari Rémi , Revenant Christine , Barbier Antoine , Noblet Marion , Ulrich Olivier , Leroy Frédéric , Jupille Jacques , Borensztein Yves , Henry Claude R. , Deville Jean-Paul , Scheurer Fabrice , Mane-Mane Jeannot , Fruchart Olivier
Published: May 2003

One challenge in the production of nanometer-sized objects with given properties is to control their growth at a macroscopic scale in situ and in real time. A dedicated ultrahigh-vacuum grazing-incidence small-angle x-ray scattering setup has been developed, yielding high sensitivity and dynamics. Its capabilities to derive the average particle shape and size and the film growth mode and ordering and to probe both surfaces and buried interfaces are illustrated for two prototypical cases: the model catalyst Pd/MgO(100) and the self-organized Co/Au(111) system. A wide range of technologically important systems can potentially be investigated in various gaseous environments.
Stress-Induced Mutagenesis in Bacteria
Authors: Bjedov Ivana , Tenaillon Olivier , Gérard Bénédicte , Souza Valeria , Denamur Erick , Radman Miroslav , Taddei François , Matic Ivan
Published: May 2003

The evolutionary significance of stress-induced mutagenesis was evaluated by studying mutagenesis in aging colonies (MAC) of
Escherichia coli
natural isolates. A large fraction of isolates exhibited a strong MAC, and the high MAC variability reflected the diversity of selective pressures in ecological niches. MAC depends on starvation, oxygen, and RpoS and adenosine 3′,5′-monophosphate regulons; thus it may be a by-product of genetic strategies for improving survival under stress. MAC could also be selected through beneficial mutations that it generates, as shown by computer modeling and the patterns of stress-inducible and constitutive mutagenesis. We suggest that irrespective of the causes of their emergence, stress-induced mutations participate in adaptive evolution.
Seismic Imaging of the Downwelling Indian Lithosphere Beneath Central Tibet
Authors: Tilmann Frederik , Ni James ,   INDEPTH III Seismic Team
Published: May 2003

A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from ∼100- to ∼400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.
Diffusion of Nonequilibrium Quasi-Particles in a Cuprate Superconductor
Authors: Gedik N. , Orenstein J. , Liang Ruixing , Bonn D. A. , Hardy W. N.
Published: May 2003

We report a transport study of nonequilibrium quasi-particles in a high-transition-temperature cuprate superconductor using the transient grating technique. Low-intensity laser excitation (at a photon energy of 1.5 electron volts) was used to introduce a spatially periodic density of quasi-particles into a high-quality untwinned single crystal of YBa
2
Cu
3
O
6.5
. Probing the evolution of the initial density through space and time yielded the quasi-particle diffusion coefficient and the inelastic and elastic scattering rates. The technique reported here is potentially applicable to precision measurements of quasi-particle dynamics not only in cuprate superconductors but in other electronic systems as well.
Characterization of Mammalian Selenoproteomes
Authors: Kryukov Gregory V. , Castellano Sergi , Novoselov Sergey V. , Lobanov Alexey V. , Zehtab Omid , Guigó Roderic , Gladyshev Vadim N.
Published: May 2003

In the genetic code, UGA serves as a stop signal and a selenocysteine codon, but no computational methods for identifying its coding function are available. Consequently, most selenoprotein genes are misannotated. We identified selenoprotein genes in sequenced mammalian genomes by methods that rely on identification of selenocysteine insertion RNA structures, the coding potential of UGA codons, and the presence of cysteine-containing homologs. The human selenoproteome consists of 25 selenoproteins.
Disrupted Timing of Discontinuous But Not Continuous Movements by Cerebellar Lesions
Authors: Spencer Rebecca M. C. , Zelaznik Howard N. , Diedrichsen Jörn , Ivry Richard B.
Published: May 2003

Patients with cerebellar damage are known to exhibit deficits in the temporal control of movements. We report that these deficits are restricted to discontinuous movements. Cerebellar patients exhibited no deficit in temporal variability when producing continuous, rhythmic movements. We hypothesize that the temporal properties of continuous movements are emergent and reflect the operation of other control parameters not associated with the cerebellum. In contrast, discontinuous movements require an explicit representation of the temporal goal, a function of the cerebellum. The requirement for explicit temporal representation provides a parsimonious account of cerebellar involvement in a range of tasks.
Modulation of Phospholipid Signaling by GLABRA2 in Root-Hair Pattern Formation
Authors: Ohashi Yohei , Oka Atsuhiro , Rodrigues-Pousada Renato , Possenti Marco , Ruberti Ida , Morelli Giorgio , Aoyama Takashi
Published: May 2003

The root-hair pattern of
Arabidopsis
is determined through a regulatory circuit composed of transcription factor genes. The homeobox gene
GLABRA2
(
GL2
) has been considered a key component, acting farthest downstream in this regulation. GL2 modified to include a transactivating function caused epidermal cells to develop ectopic root hairs or root hair–like structures. With this system, the phospholipase Dζ1 gene (
AtPLD
ζ
1
) was identified as a direct target of GL2. Inducible expression of
AtPLD
ζ
1
promoted ectopic root-hair initiation. We conclude that GL2 exerts its regulatory effect on root-hair development through modulation of phospholipid signaling.
Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo
Authors: Larson Daniel R. , Zipfel Warren R. , Williams Rebecca M. , Clark Stephen W. , Bruchez Marcel P. , Wise Frank W. , Webb Watt W.
Published: May 2003

The use of semiconductor nanocrystals (quantum dots) as fluorescent labels for multiphoton microscopy enables multicolor imaging in demanding biological environments such as living tissue. We characterized water-soluble cadmium selenide–zinc sulfide quantum dots for multiphoton imaging in live animals. These fluorescent probes have two-photon action cross sections as high as 47,000 Goeppert-Mayer units, by far the largest of any label used in multiphoton microscopy. We visualized quantum dots dynamically through the skin of living mice, in capillaries hundreds of micrometers deep. We found no evidence of blinking (fluorescence intermittency) in solution on nanosecond to millisecond time scales.
A Bond-Fluctuation Mechanism for Stochastic Switching in Wired Molecules
Authors: Ramachandran Ganesh K. , Hopson Theresa J. , Rawlett Adam M. , Nagahara Larry A. , Primak Alex , Lindsay Stuart M.
Published: May 2003

Stochastic on-off conductivity switching observed in phenylene-ethynylene oligomers has been explained in terms of changes in ring conformations, or electron localization, or both. We report the observation of stochastic on-off switching in the simplest of wired molecules: octanedithiol, decanedithiol, and dodecanedithiol bonded on an Au(111) surface. Stochastic switching was observed even when a top gold contact was pressed on by a conducting atomic force microscope tip at constant force. The rate of switching increased substantially at 60°C, a temperature at which these films are commonly annealed. Because such switching in alkanethiols is unlikely to be caused by internal molecular electronic changes and cannot be fully accounted for by breaking of the top contact, we argue that the cause is the well-known mobility of molecules tethered to gold via a thiol linkage.
Atomic Resolution Imaging of a Carbon Nanotube from Diffraction Intensities
Authors: Zuo J. M. , Vartanyants I. , Gao M. , Zhang R. , Nagahara L. A.
Published: May 2003

Atomic imaging of three-dimensional structures has required a crystal in diffraction or a lens in electron imaging. Whereas diffraction achieves very high resolution by averaging over many cells, imaging gives localized structural information, such as the position of a single dopant atom. However, lens aberrations limit electron imaging resolution to about 1 angstrom. Resolution is reduced further by low contrast from weakscattering or from the limitations on electron dose for radiation-sensitive molecules. We show that both high resolution and high contrast can be achieved by imaging from diffraction with a nanometer-sized coherent electron beam. The phase problem is solved by oversampling and iterative phase retrieval. We apply this technique to image a double-wall carbon nanotube at 1-angstrom resolution, revealing the structure of two tubes of different helicities. Because the only requirement for imaging is a diffraction pattern sampled below the Nyquist frequency, our technique has the potential to image nonperiodic nanostructures, including biological macromolecules, at diffraction intensity–limited resolutions.
A Prescription for Peace
Authors: Carter Ashton B.
Published: May 2003

No More Killing Fields
Preventing Deadly Conflict. David A. Hamburg. Rowman and Littlefield, Lanham, MD, 2002. 391 pp. $39.95. ISBN 0-7425-1674-1.

The best approach to preserving peace and preventing war and terrorism, Hamburg argues, lies in cooperative, international efforts that support preventative diplomacy, build democratic institutions, and upgrade socioeconomic development.
Where Have All the Mammoth Gone?
Authors: Holliday Vance T.
Published: May 2003

The Early Settlement of North America
The Clovis Era. Gary Haynes. Cambridge University Press, Cambridge, 2002. 359 pp. $80, £60. ISBN 0-521-81900-8. Paper, $29, £21.95. ISBN 0-521-52463-6.

After reviewing previous research and the available evidence on the Clovis culture, Haynes presents an interpretation that reflects recent findings from biology, ecology, behavior, and archaeology.
Finding Functional Features in
Saccharomyces
Genomes by Phylogenetic Footprinting
Authors: Cliften Paul , Sudarsanam Priya , Desikan Ashwin , Fulton Lucinda , Fulton Bob , Majors John , Waterston Robert , Cohen Barak A. , Johnston Mark
Published: May 2003

The sifting and winnowing of DNA sequence that occur during evolution cause nonfunctional sequences to diverge, leaving phylogenetic footprints of functional sequence elements in comparisons of genome sequences. We searched for such footprints among the genome sequences of six
Saccharomyces
species and identified potentially functional sequences. Comparison of these sequences allowed us to revise the catalog of yeast genes and identify sequence motifs that may be targets of transcriptional regulatory proteins. Some of these conserved sequence motifs reside upstream of genes with similar functional annotations or similar expression patterns or those bound by the same transcription factor and are thus good candidates for functional regulatory sequences.
Asteroseismology of HD 129929: Core Overshooting and Nonrigid Rotation
Authors: Aerts C. , Thoul A. , Daszyńska J. , Scuflaire R. , Waelkens C. , Dupret M. A. , Niemczura E. , Noels A.
Published: May 2003

We have gathered and analyzed 1493 high-quality multicolor Geneva photometric data taken over 21 years of the B3Vstar HD 129929. We detect six frequencies, among which appear the effects of rotational splitting with a spacing of ∼0.0121 cycles per day, which implies that the star rotates very slowly. A nonadiabatic analysis of the oscillations allows us to constrain the metallicity of the star to
Z
ϵ [0.017,0.022], which agrees with a similar range derived from spectroscopic data. We provide evidence for the occurrence of core convective overshooting in the star, with α
ov
= 0.10 ± 0.05, and we rule out rigid rotation.
Purification and Properties of an Intracellular 3-Hydroxybutyrate-Oligomer Hydrolase (PhaZ2) in
Ralstonia eutropha
H16 and Its Identification as a Novel Intracellular Poly(3-Hydroxybutyrate) Depolymerase
Authors: Kobayashi Teruyuki , Shiraki Mari , Abe Tomoko , Sugiyama Akinori , Saito Terumi
Published: May 2003

An intracellular 3-hydroxybutyrate (3HB)-oligomer hydrolase (PhaZ2
Reu
) of
Ralstonia eutropha
was purified from
Escherichia coli
harboring a plasmid containing
phaZ2

Reu

. The purified enzyme hydrolyzed linear and cyclic 3HB-oligomers. Although it did not degrade crystalline poly(3-hydroxybutyrate) (PHB), the purified enzyme degraded artificial amorphous PHB at a rate similar to that of the previously identified intracellular PHB (iPHB) depolymerase (PhaZ1
Reu
). The enzyme appeared to be an endo-type hydrolase, since it actively hydrolyzed cyclic 3HB-oligomers. However, it degraded various linear 3HB-oligomers and amorphous PHB in the fashion of an exo-type hydrolase, releasing one monomer unit at a time. PhaZ2 was found to bind to PHB inclusion bodies and as a soluble enzyme to cell-free supernatant fractions in
R. eutropha
; in contrast, PhaZ1 bound exclusively to the inclusion bodies. When
R. eutropha
H16 was cultivated in a nutrient-rich medium, the transient deposition of PHB was observed: the content of PHB was maximized in the log growth phase (12 h, ca. 14% PHB of dry cell weight) and decreased to a very low level in the stationary phase (ca. 1% of dry cell weight). In each
phaZ1
-null mutant and
phaZ2
-null mutant, the PHB content in the cell increased to ca. 5% in the stationary phase. A double mutant lacking both
phaZ1
and
phaZ2
showed increased PHB content in the log phase (ca. 20%) and also an elevated PHB level (ca. 8%) in the stationary phase. These results indicate that PhaZ2 is a novel iPHB depolymerase, which participates in the mobilization of PHB in
R. eutropha
along with PhaZ1.
SigM, an Extracytoplasmic Function Sigma Factor ofBacillus subtilis, Is Activated in Response to Cell Wall Antibiotics, Ethanol, Heat, Acid, and Superoxide Stress
Authors: Thackray Penny D. , Moir Anne
Published: May 2003

The extracytoplasmic function sigma M ofBacillus subtilisis required for normal cell growth under salt stress. It is expressed maximally during exponential growth and is further induced by the addition of 0.7 M NaCl. The promoter region of thesigMoperon contains two promoters; one (PA) is sigma A dependent, and the other (PM) is sigma M dependent. These have been placed separately at theamylocus, directing expression of alacZreporter gene. Only the PMfusion responded to salt induction. This promoter, which was responsive to the level of active sigma M in the cell, was also induced by 5% ethanol, by vancomycin, bacitracin, or phosphomycin (inhibitors of cell wall biosynthesis; 2 μg per ml), and by heat shock of 50°C for 10 min. It was very strongly induced by acid (pH 4.3) and 80 μM paraquat, but after a 15- to 30-min delay. There was no induction by alkali (pH 9), 5 mM H2O2, the detergents 0.1% Triton X-100 and 0.1% Tween 20, or 50 μM monensin. In addition to their reduced tolerance to salt, null mutants ofsigMwere unable to grow at pH 4.3 and lysed after exposure to 5% ethanol. Genes regulated by SigM were also tested for their response to pH 4.3, 5% ethanol, and 2 μg of vancomycin per ml. Expression of the genes may have been activated by increased levels of sigma M, but at least some were also subject to additional controls, as they responded to one type of stress but not another. Expression ofyrhJ, which encodes a cytochrome P450/NADPH reductase, was induced in response to acid and vancomycin.yraAexpression was acid, ethanol, and vancomycin induced, whereasyjbDshowed only ethanol induction. YraA protein was extremely important to acid survival—a mutation inyraA, like asigMmutation, resulted in the failure ofB. subtilisto grow at pH 4.3. Sigma M is therefore involved in maintaining membrane and cell wall integrity in response to several different stresses in exponential growth phase and is activated by such stresses.
ThettsAGene Is Required for Low-Calcium-Induced Type III Secretion of Yop Proteins and Virulence ofYersinia enterocoliticaW22703
Authors: DeBord Kristin L. , Galanopoulos Nicholas S. , Schneewind Olaf
Published: May 2003

PathogenicYersiniaspecies use a virulence-plasmid encoded type III secretion pathway to escape the innate immune response and to establish infections in lymphoid tissues. At least 22 secretion machinery components are required for type III transport of 14 different Yop proteins, and 10 regulatory factors are responsible for activating this pathway in response to environmental signals. Although the genes for these products are located on the 70-kb virulence plasmid ofYersinia, this extrachromosomal element does not appear to harbor genes that provide for the sensing of environmental signals, such as calcium-, glutamate-, or serum-sensing proteins. To identify such genes, we screened transposon insertion mutants ofY. enterocoliticaW22703 for defects in type III secretion and identifiedttsA, a chromosomal gene encoding a polytopic membrane protein.ttsAmutant yersiniae synthesize reduced amounts of Yops and display a defect in low-calcium-induced type III secretion of Yop proteins.ttsAmutants are also severely impaired in bacterial motility, a phenotype which is likely due to the reduced expression of flagellar genes. All of these defects were restored by complementation with plasmid-encoded wild-typettsA. LcrG is a repressor of theYersiniatype III pathway that is activated by an environmental calcium signal. Mutation of thelcrGgene in attsAmutant strain restored the type III secretion of Yop proteins, although the double mutant strain secreted Yops in the presence and absence of calcium, similar to the case for mutants that are defective inlcrGgene function alone. To examine the role ofttsAin the establishment of infection, we measured the bacterial dose required to produce an acute lethal disease following intraperitoneal infection of mice. ThettsAinsertion caused a greater-than-3-log-unit reduction in virulence compared to that of the parental strain.
PhoP-Responsive Expression of theSalmonella entericaSerovar TyphimuriumslyAGene
Authors: Norte Valia A. , Stapleton Melanie R. , Green Jeffrey
Published: May 2003

The SlyA protein ofSalmonella entericaserovar Typhimurium is a member of the MarR family of transcription regulators and is required for virulence and survival in professional macrophages. Isolated SlyA protein was able to bind a specific DNA target without posttranslational modification. This suggested that SlyA might not be activated by directly sensing an external signal but rather that the intracellular concentration of SlyA is enhanced in appropriate environments through the action of other transcription factors. Analysis ofslyAtranscription reveals the presence of a promoter region located upstream of the previously recognized SlyA repressed promoter. The newly identified upstream promoter region did not respond to SlyA but was activated by Mg(II) starvation in a PhoP-dependent manner. We present here evidence for a direct link between two transcription factors (PhoP and SlyA) crucial forSalmonellavirulence.
The
Pseudomonas fluorescens
AlgG Protein, but Not Its Mannuronan C-5-Epimerase Activity, Is Needed for Alginate Polymer Formation
Authors: Gimmestad Martin , Sletta Håvard , Ertesvåg Helga , Bakkevig Karianne , Jain Sumita , Suh Sang-jin , Skjåk-Bræk Gudmund , Ellingsen Trond E. , Ohman Dennis E. , Valla Svein
Published: May 2003

Bacterial alginates are produced as 1-4-linked β
-d-
mannuronan, followed by epimerization of some of the mannuronic acid residues to α
-l-
guluronic acid. Here we report the isolation of four different epimerization-defective point mutants of the periplasmic
Pseudomonas fluorescens
mannuronan C-5-epimerase AlgG. All mutations affected amino acids conserved among AlgG-epimerases and were clustered in a part of the enzyme also sharing some sequence similarity to a group of secreted epimerases previously reported in
Azotobacter vinelandii
. An
algG
-deletion mutant was constructed and found to produce predominantly a dimer containing a 4-deoxy
-l-
erythro
-hex-4-enepyranosyluronate residue at the nonreducing end and a mannuronic acid residue at the reducing end. The production of this dimer is the result of the activity of an alginate lyase, AlgL, whose in vivo activity is much more limited in the presence of AlgG. A strain expressing both an epimerase-defective (point mutation) and a wild-type epimerase was constructed and shown to produce two types of alginate molecules: one class being pure mannuronan and the other having the wild-type content of guluronic acid residues. This formation of two distinct classes of polymers in a genetically pure cell line can be explained by assuming that AlgG is part of a periplasmic protein complex.
Protein Synthesis in
Escherichia coli
with Mischarged tRNA
Authors: Min Bokkee , Kitabatake Makoto , Polycarpo Carla , Pelaschier Joanne , Raczniak Gregory , Ruan Benfang , Kobayashi Hiroyuki , Namgoong Suk , Söll Dieter
Published: May 2003

Two types of aspartyl-tRNA synthetase exist: the discriminating enzyme (D-AspRS) forms only Asp-tRNA
Asp
, while the nondiscriminating one (ND-AspRS) also synthesizes Asp-tRNA
Asn
, a required intermediate in protein synthesis in many organisms (but not in
Escherichia coli
). On the basis of the
E. coli trpA34
missense mutant transformed with heterologous ND-
aspS
genes, we developed a system with which to measure the in vivo formation of Asp-tRNA
Asn
and its acceptance by elongation factor EF-Tu. While large amounts of Asp-tRNA
Asn
are detrimental to
E. coli
, smaller amounts support protein synthesis and allow the formation of up to 38% of the wild-type level of missense-suppressed tryptophan synthetase.
The
Stigmatella aurantiaca
Homolog of
Myxococcus xanthus
High-Mobility-Group A-Type Transcription Factor CarD: Insights into the Functional Modules of CarD and Their Distribution in Bacteria
Authors: Cayuela María L. , Elías-Arnanz Montserrat , Peñalver-Mellado Marcos , Padmanabhan S. , Murillo Francisco J.
Published: May 2003

Transcriptional factor CarD is the only reported prokaryotic analog of eukaryotic high-mobility-group A (HMGA) proteins, in that it has contiguous acidic and AT hook DNA-binding segments and multifunctional roles in
Myxococcus xanthus
carotenogenesis and fruiting body formation. HMGA proteins are small, randomly structured, nonhistone, nuclear architectural factors that remodel DNA and chromatin structure. Here we report on a second AT hook protein, CarD
Sa
, that is very similar to CarD and that occurs in the bacterium
Stigmatella aurantiaca
. CarD
Sa
has a C-terminal HMGA-like domain with three AT hooks and a highly acidic adjacent region with one predicted casein kinase II (CKII) phosphorylation site, compared to the four AT hooks and five CKII sites in CarD. Both proteins have a nearly identical 180-residue N-terminal segment that is absent in HMGA proteins. In vitro, CarD
Sa
exhibits the specific minor-groove binding to appropriately spaced AT-rich DNA that is characteristic of CarD or HMGA proteins, and it is also phosphorylated by CKII. In vivo, CarD
Sa
or a variant without the single CKII phosphorylation site can replace CarD in
M. xanthus
carotenogenesis and fruiting body formation. These two cellular processes absolutely require that the highly conserved N-terminal domain be present. Thus, three AT hooks are sufficient, the N-terminal domain is essential, and phosphorylation in the acidic region by a CKII-type kinase can be dispensed with for CarD function in
M. xanthus
carotenogenesis and fruiting body development. Whereas a number of hypothetical proteins homologous to the N-terminal region occur in a diverse array of bacterial species, eukaryotic HMGA-type domains appear to be confined primarily to myxobacteria.
Relaxed Specificity of the R1162 Nickase: a Model for Evolution of a System for Conjugative Mobilization of Plasmids
Authors: Becker Eric C. , Meyer Richard J.
Published: May 2003

The primary DNA processing protein for conjugative mobilization of the plasmid R1162 is the transesterase MobA, which acts at a unique site on the plasmid, the origin of transfer (
oriT
). Both MobA and
oriT
are members of a large family of related elements that are widely distributed among bacteria. Each
oriT
consists of a highly conserved core and an adjacent region that is required for binding by its cognate MobA. The sequence of the adjacent region is important in determining the specificity of the interaction between the Mob protein and the
oriT
DNA. However, the R1162 MobA is active on the
oriT
of pSC101, another naturally occurring plasmid. We show here that MobA can recognize
oriT
s having different sequences in the adjacent region and, with varying frequencies, can cleave these
oriT
s at the correct position within the core. Along with the structure of the
oriT
s themselves, these characteristics suggest a model for the evolution of this group of transfer systems.