bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracheostomy timing and the duration of weaning in patients with acute respiratory failure
Authors: Boynton Jackie H , Hawkins Kenneth , Eastridge Brian J , O'Keefe Grant E
Published: June 2004

Introduction

The effect of various airway management strategies, such as the timing of tracheostomy, on liberation from mechanical ventilation (MV) is uncertain. We tested the hypothesis that tracheostomy, when performed prior to active weaning, does not influence the duration of weaning or of MV in comparison with a more selective use of tracheostomy.

Patients and methods

In this observational prospective cohort study, surgical patients requiring ≥ 72 hours of MV were followed prospectively. Patients undergoing tracheostomy prior to any active weaning attempts (early tracheostomy [ET]) were compared with patients in whom initial weaning attempts were made with the endotracheal tube in place (selective tracheostomy [ST]).

Results

We compared the duration of weaning, the total duration of MV and the frequency of fatigue and pneumonia. Seventy-four patients met inclusion criteria. Twenty-one patients in the ET group were compared with 53 patients in the ST group (47% of whom ultimately underwent tracheostomy). The median duration of weaning was shorter (3 days versus 6 days, P = 0.05) in patients in the ET group than in the ST group, but the duration of MV was not (median [interquartile range], 11 days [9–26 days] in the ET group versus 13 days [8–21 days] in the ST group). The frequencies of fatigue and pneumonia were lower in the ET group patients.

Discussion

Determining the ideal timing of tracheostomy in critically ill patients has been difficult and often subjective. To standardize this process, it is important to identify objective criteria to identify patients most likely to benefit from the procedure. Our data suggest that in surgical patients with resolving respiratory failure, a patient who meets typical criteria for a trial of spontaneous breathing but is not successfully extubated within 24 hours may benefit from a tracheostomy. Our data provide a framework for the conduct of a clinical trial in which tracheostomy timing can be assessed for its impact on the duration of weaning.

Conclusion

Tracheostomy prior to active weaning may hasten liberation from ventilation and reduce complications. However, this does not reduce the overall duration of MV.
Activation of murine macrophages byNeisseria meningitidisand IFN-γ in vitro: distinct roles of class A scavenger and Toll-like pattern recognition receptors in selective modulation of surface phenotype
Authors: Mukhopadhyay Subhankar , Peiser Leanne , Gordon Siamon
Published: June 2004

Innate and adaptive immune activation of macrophages (Mφ) by microorganisms and antigen-activated lymphoid cells, respectively, plays an important role in host defense and immunopathology. Antigen-presenting cells express a range of pattern recognition receptors including the class A types I and II scavenger receptors (SR-A) and Toll-like receptors (TLR). Recognition of microbial products by SR-A and TLR controls uptake, killing, altered gene expression, and the adaptive immune response; however, the contribution of each receptor and interplay with cytokine stimuli such as interferon-γ (IFN-γ) are not defined. We used Neisseria meningitidis (NM), a potent activator of innate immunity, and IFN-γ, a protoypic T helper cell type 1 proinflammatory cytokine, to compare surface antigens, secretion of mediators, and receptor functions in elicited peritoneal Mφ from wild-type and genetically modified mouse strains. We show that these stimuli regulate major histocompatibility complex type II (MHC-II) and costimulatory molecules differentially, as well as expression of the mannose receptor and of Mφ receptor with collagenous structure (MARCO), a distinct SR-A, which provides a selective marker for innate activation. In combination, NM inhibited up-regulation of MHC-II by IFN-γ while priming enhanced release of tumor necrosis factor α and nitric oxide. The SR-A contributes to phagocytosis of the organisms but not to their ability to induce CD80, CD86, and MARCO or to inhibit MHC-II. Conversely, studies with lipopolysaccharide (LPS)-deficient organisms and/or TLR-4 mutant mice showed that LPS and TLR-4 are at least partially required to induce CD80, CD86, and MARCO, but LPS is not required to inhibit MHC-II. These studies provide an experimental model and identify surface markers for analysis of innate and acquired immune activation of Mφ.
Eformoterol n-of-1 trials in chronic obstructive pulmonary disease poorly reversible to salbutamol
Authors: Smith B J , Appleton S L , Veale A J , McElroy H J , Veljkovic D , Saccoia L
Published: June 2004

Aims: Benefits of long acting beta 2 agonists are unclear for severe chronic obstructive pulmonary disease (COPD) patients with poor response to short acting bronchodilators. We aimed to evaluate 1) effects of eformoterol in such patients using a ‘n-of-1’ double crossover study design, and 2) aggregate data as a double-blind, double crossover randomized control trial. Methods: Subjects with forced expiratory volume in one second (FEV1) < 60% predicted, and poor response to short acting bronchodilators were studied six times over 18 weeks. During that time they were prescribed four weeks of either eformoterol or placebo, followed by the alternate, and then a second crossover. Four-weekly measures included six minute walk distance (6MWD), FEV1, previous two weeks of symptoms, and chronic respiratory questionnaire (CRQ) including treatment goal items. Results: Of 27 original subjects (21 male, mean age of 70 years, five smokers, mean prebronchodilator FEV1, 36% predicted), one subject had clinically significant concordant improvement in the CRQ dyspnoea domain and 6MWD (by 51 metres), but not for other outcomes. There were no concordant improvements in any other subjects. Aggregate double crossover data analysis demonstrated no improvement in any outcome measures. Conclusions: The ‘n-of-1’ study design and aggregate data analysis demonstrated lack of benefit from eformoterol in COPD patients with poor response to short acting bronchodilators.
On the Occurrence of Transition States in Celestial Mechanics
Authors: JAFFÉ CHARLES , UZER T
Published: June 2004

Abstract: The transition state is a central concept in the study of chemical reactions. The basic idea is that state space (phase space) can be partitioned into two volumes; the first corresponding to reactants and the second to products. Chemists call the boundary between these two regions the transition state. The rate of a chemical reaction is then discussed in terms the of the flow across the transition state. These ideas can also be applied with good effect to celestial problems. This paper outlines the chemists' view of molecular dynamics and then illustrates its application to problem of transport in celestial mechanics.
Migration of Interplanetary Dust
Authors: IPATOV S I. , MATHER J C. , TAYLOR P A.
Published: June 2004

Abstract: We numerically investigate the migration of dust particles with initial orbits close to those of the numbered asteroids, observed trans‐Neptunian objects, and comet Encke. The fraction of silicate asteroidal particles that collided with the Earth during their lifetime varied from 11% for 100 micron particles to 0.008% for 1 micron particles. Almost all asteroidal particles with diameter d≥ 4 microns collided with the Sun. For migrating asteroidal dust particles, the peaks in semimajor axis distribution at the n:(n+ 1) resonances with Earth and Venus, and the gaps associated with the 1:1 resonances with these planets are more pronounced for larger particles. The probability of collisions of cometary particles with the Earth is smaller than for asteroidal particles, and this difference is greater for larger particles.
Stability of Relative Equilibria in the Full Two‐Body Problem
Authors: SCHEERES DJ
Published: June 2004

Abstract: The stability of relative equilibrium solutions for the interaction of two massive bodies is explored. We restrict ourselves to the interaction between an ellipsoid and a sphere, both with finite mass. The study of this problem has application to modeling the relative dynamics of binary asteroids, the motion of spacecraft about small bodies, and the dynamics of gravity gradient satellites. The relative equilibrium can be parameterized by a few constants, including the mass ratio of the two bodies, the shape of the ellipsoid, and the normalized distance between the two bodies. Planar stability is characterized over this range of parameter values. When restricted to motion in the symmetry plane, the dynamical problem can be reduced to a two‐degrees of freedom Hamiltonian system, which allows for an efficient computation of stability characteristics of the relative equilibria. Future work will look at full stability of these relative equilibria.
Coordinated Orbit Transfer for Satellite Clusters
Authors: ZHANG FUMIN , KRISHNAPRASAD P S.
Published: June 2004

Abstract:We propose a control law that allows a satellite formation to achieve orbit transfer. During the transfer, the formation can be either maintained or modified to a desired formation. Based on the orbit transfer control law proposed by Chang, Chichka, and Marsden for single satellite, we add coupling terms to the summation of Lyapunov functions for single satellites. These terms are functions of the difference between the mean anomalies (or perigee passage times) of formation members. The asymptotic stability of the desired formation in desired orbits is proved.
Hamiltonian Modelling of Relative Motion
Authors: KASDIN N JEREMY , GURFIL PINI
Published: June 2004

Abstract: This paper presents a Hamiltonian approach to modelling relative spacecraft motion based on derivation of canonical coordinates for the relative state‐space dynamics. The Hamiltonian formulation facilitates the modelling of high‐order terms and orbital perturbations while allowing us to obtain closed‐form solutions to the relative motion problem. First, the Hamiltonian is partitioned into a linear term and a high‐order term. The Hamilton‐Jacobi equations are solved for the linear part by separation, and new constants for the relative motions are obtained, they are called epicyclic elements. The influence of higher order terms and perturbations, such as the oblateness of the Earth, are incorporated into the analysis by a variation of parameters procedure. Closed‐form solutions for J2‐ and J4‐invariant orbits and for periodic high‐order unperturbed relative motion, in terms of the relative motion elements only, are obtained.
Near‐Optimal Reconfiguration and Maintenance of Close Spacecraft Formations
Authors: LOVELL T A , TRAGESSER S G
Published: June 2004

Abstract: This paper investigates orbit guidance algorithms for formation flying experiments. The relative motion of one satellite about a reference satellite is formulated in terms of a set of parameters that clearly describe the size, shape, and orientation of the formation. A nominal three‐impulse burn maneuver algorithm is presented that is applicable for both reconfiguration and maintenance of spacecraft formations. Two methods of implementing the algorithm are discussed, one involving fixed times between each burn and one allowing the wait times to vary. The implications of employing four or more impulses for maneuvers are assessed. Examples applying the algorithm to various formation scenarios are presented, along with practical implications of each result.
Control of Satellite Clusters in Elliptic Orbit with Limited Communication
Authors: CHICHKA DAVID F. , BELANGER GENE , SPEYER JASON L.
Published: June 2004

Abstract: The cooperative control of satellite clusters in elliptical, low‐Earth orbit is studied, with the goal of minimizing the necessary information passed among the individual satellites in the cluster. We investigate two possible control paradigms in this paper. The system is described using linearized equations of motion, allowing it to be expressed as a time‐varying linear system. The control objective is to attain a required formation at a specified point along the orbit. A decentralized controller is used, in which each satellite maintains a local estimate of the overall state of the cluster. These estimates, along with any control information, are shared after any satellite executes a control action. The second paradigm is an extension of the first, in which state estimates are never shared, and only the control information is passed. In each case, less information being passed results in a higher computational burden on each satellite. Simulation results show cyclic errors, likely induced by higher‐order terms in eccentricity and inclinations. The controller that shares state estimates performs much better than the controller that passes only control information.
Optimal Plane Changes Using Third‐Body Forces
Authors: VILLAC B F , SCHEERES D J
Published: June 2004

Abstract: The fuel optimality of third‐body driven plane changes (i.e., plane changes performed by using third‐body forces) over one‐impulse transfers is investigated numerically and analytically. In particular, the range of third‐body driven plane changes that are realizable is shown to be restricted and one impulse must be used in the uncovered regions. However, when third‐body driven plane changes are realizable, it is shown that they are always optimal above a certain critical value (about 40°) that depends on the initial condition. Contour plots of optimal ΔV values to perform a desired plane changes are given.
Background and Applications of Astrodynamics for Space Missions of the Johns Hopkins Applied Physics Laboratory
Authors: DUNHAM DAVID W. , FARQUHAR ROBERT W.
Published: June 2004

Abstract: This paper describes astrodynamic techniques applied to develop special orbital designs for past and future space missions of the Applied Physics Laboratory (APL) of Johns Hopkins University, and background about those techniques. The paper does not describe the long history of low Earth‐orbiting missions at APL, but rather concentrates on the astrodynamically more interesting high‐altitude and interplanetary missions that APL has undertaken in recent years. The authors developed many of their techniques in preparation for, and during, the Third International Sun‐Earth Explorer (ISEE‐3) halo orbit mission while they worked for the Goddard Space Flight Center (GSFC) of NASA during the 1970s and 1980s. Later missions owed much to the ground breaking work of the trajectory designs for ISEE‐3 (later known as the International Cometary Explorer, or ICE). This experience, and other new ideas, were applied to the APL near Earth asteroid rendezvous (NEAR) and comet nucleus tour (CONTOUR) discovery missions, as well as to APL's future MESSENGER, STEREO, and New Horizons missions. These will be described in the paper.
Advanced Stellar Compass Onboard Autonomous Orbit Determination, Preliminary Performance
Authors: BETTO MAURIZIO , JØRGENSEN JOHN L. , JØRGENSEN PETER S. , DENVER TROELZ
Published: June 2004

Abstract: Deep space exploration is in the agenda of the major space agencies worldwide; certainly the European Space Agency (SMART Program) and the American NASA (New Millennium Program) have set up programs to allow the development and the demonstration of technologies that can reduce the risks and the cost of deep space missions. From past experience, it appears that navigation is the Achilles heel of deep space missions. Performed on ground, this imposes considerable constraints on the entire system and limits operations. This makes it is very expensive to execute, especially when the mission lasts several years and, furthermore, it is not failure tolerant. Nevertheless, to date, ground navigation has been the only viable solution. The technology breakthrough of advanced star trackers, like the advanced stellar compass (ASC), might change this situation. Indeed, exploiting the capabilities of this instrument, the authors have devised a method to determine the orbit of a spacecraft autonomously, onboard, and without a priori knowledge of any kind. The solution is robust and fast. This paper presents the preliminary performance obtained during the ground testing in August 2002 at the Mauna Kea Observatories. The main goals were: (1) to assess the robustness of the method in solving autonomously, onboard, the position lost‐in‐space problem; (2) to assess the preliminary accuracy achievable with a single planet and a single observation; (3) to verify the autonomous navigation (AutoNav) module could be implemented into an ASC without degrading the attitude measurements; and (4) to identify the areas of development and consolidation. The results obtained are very encouraging.
New Orbits for the n‐Body Problem
Authors: VANDERBEI ROBERT J.
Published: June 2004

Abstract: In this paper, we consider minimizing the action functional as a method for numerically discovering periodic solutions to the n‐body problem. With this method, we can find a large number of choreographies and other more general solutions. We show that most of the solutions found, including all but one of the choreographies, are unstable. It appears to be much easier to find unstable solutions to the n‐body problem than stable ones. Simpler solutions are more likely to be stable than exotic ones.
A Survey of Propulsion Options for Cargo and Piloted Missions to Mars
Authors: SANKARAN K , CASSADY L , KODYS A D , CHOUEIRI E Y
Published: June 2004

Abstract: In this paper, high‐power electric propulsion options are surveyed in the context of cargo and piloted missions to Mars. A low‐thrust trajectory optimization program (raptor) is utilized to analyze this mission. Candidate thrusters are chosen based upon demonstrated performance in the laboratory. Hall, self‐field magnetoplasmadynamic (MPDT), self‐field lithium Lorentz force accelerator (LiLFA), arcjet, and applied‐field LiLFA systems are considered for this mission. In this first phase of the study, all thrusters are assumed to operate at a single power level (regardless of the efficiency‐power curve), and the thruster specific mass and power plant specific mass are taken to be the same for all systems. Under these assumptions, for a 7.5 MW, 60 mT payload, piloted mission, the self‐field LiLFA results in the shortest trip time (340 days) with a reasonable propellant mass fraction of 57% (129 mT). For a 150 kW, 9 mT payload, cargo mission, both the applied‐field LiLFA and the Hall thruster seem reasonable choices with propellant mass fractions of 42 to 45%(7 to 8 mT). The Hall thrusters provide better trip times (530‐570 days) compared to the applied‐field LiLFA (710 days) for the relatively less demanding mission.
Spaciotemporal Association and Bone Morphogenetic Protein Regulation of Sclerostin and Osterix Expression during Embryonic Osteogenesis
Authors: Ohyama Yoshio , Nifuji Akira , Maeda Yukiko , Amagasa Teruo , Noda Masaki
Published: June 2004

Sclerostin (SOST), a member of the cystine-knot superfamily, is essential for proper skeletogenesis because a loss-of-function mutation in the SOST gene results in sclerosteosis featured with massive bone growth in humans. To understand the function of SOST in developmental skeletal tissue formation, we examined SOST gene expression in embryonic osteogenesis in vitro and in vivo. During osteoblastic differentiation in primary calvarial cells, the levels of SOST expression were increased along with those of alkaline phosphatase activity and nodule formation. In situ hybridization study revealed that SOST mRNA expression was observed in the digits in embryonic 13-d limb buds, and SOST expression was observed in osteogenic front in embryonic 16.5-d postcoitus embryonic calvariae, and this expression persisted in the peripheral area of cranial bone in the later developmental stage (embryonic 18.5-d post coitum). These temporal and spacial expression patterns in vivo and in vitro were in parallel to those of osterix (Osx), which is a critical transcriptional factor for bone formation. Similar coexpression of SOST and Osx mRNA was observed when the primary osteoblastic calvarial cells were cultured in the presence of bone morphogenetic protein (BMP)2 in vitro. Moreover, endogenous expression of SOST and Osx mRNA was inhibited by infection of noggin-expression adenovirus into the primary osteoblastic calvarial cells, suggesting that endogenous BMPs are required for these cells to express SOST and Osx mRNA. Thus, expression and regulation of SOST under the control of BMP were closely associated with those of Osx in vivo and in vitro.
Alcohol Alters Luteinizing Hormone Secretion in Immature Female Rhesus Monkeys by a Hypothalamic Action
Authors: Dissen Gregory A. , Dearth Robert K. , Scott H. Morgan , Ojeda Sergio R. , Dees W. Les
Published: June 2004

We determined whether the effect of alcohol (ALC) to suppress LH secretion in immature female monkeys is due to a hypothalamic or pituitary site of action. Beginning at 20 months of age, four monkeys received a single intragastric dose of ALC (2.4 g/kg), and four monkeys received an equal volume of a saline/sucrose solution daily until they were 36 months old. For the hypothalamic response test, two basal samples (3.5 ml) were collected at 15-min intervals via the saphenous vein, and then N-methyl-d-l-aspartic acid (NMA; 20 mg/kg) was given iv and four more blood samples collected. Three weeks later, this protocol was repeated except LH-releasing hormone (LHRH) (5 μg/kg) was used to test pituitary responsiveness. NMA or LHRH was administered 3 h after the ALC. After the pituitary challenge, each monkey was ovariectomized and 6 wk later, implanted with an indwelling subclavian vein catheter. Blood samples were drawn every 10 min for 8 h to assess effects of ALC on post-ovariectomy LH levels and the profile of LH pulsatile secretion. The hypothalamic challenge showed NMA stimulated LH release in control monkeys, an action that was blocked by ALC. The pituitary challenge revealed that LHRH stimulated LH release equally well in control and ALC-treated monkeys. A post-ovariectomy rise in LH was observed in both groups, but levels were 45% lower in ALC-treated monkeys. This reduction was attributed to an ALC-induced suppression of both baseline and amplitude of pulses. Results demonstrate that the ALC-induced suppression of LH in immature female rhesus monkeys is due to an inhibitory action of the drug at the hypothalamic level.
ERK signaling is required for eye-specific retino-geniculate segregation
Authors: Naska Sibel , Cenni Maria Cristina , Menna Elisabetta , Maffei Lamberto
Published: June 2004

In the mammalian visual system, retinal ganglion cell (RGC) projections from each eye, initially intermixed within the dorsal-lateral geniculate nucleus (dLGN), become segregated during the early stages of development,occupying distinct eye-specific layers. Electrical activity has been suggested to play a role in this process; however, the cellular mechanisms underlying eye-specific segregation are not yet defined. It is known that electrical activity is among the strongest activators of the extracellular signal-regulated kinase (ERK) pathway. Moreover, the ERK pathway is involved in the plasticity of neural connections during development. We examine the role of ERK in the segregation of retinal afferents into eye-specific layers in the dLGN. The activation of this signaling cascade was selectively blocked along the retino-thalamic circuitry by specific inhibitors, and the distribution of RGC fibers in the dLGN was studied. Our results demonstrate that the blockade of ERK signaling prevents eye-specific segregation in the dLGN, providing evidence that ERK pathway is required for the proper development of retino-geniculate connections. Of particular interest is the finding that ERK mediates this process both at the retinal and geniculate level.
Differential requirements for Smad4 in TGFβ-dependent patterning of the early mouse embryo
Authors: Chu Gerald C. , Dunn N. Ray , Anderson Dorian C. , Oxburgh Leif , Robertson Elizabeth J.
Published: June 2004

Genetic and biochemical data have identified Smad4 as a key intracellular effector of the transforming growth factor β (TGFβ superfamily of secreted ligands. In mouse, Smad4-null embryos do not gastrulate, a phenotype consistent with loss of other TGFβ-related signaling components. Chimeric analysis reveals a primary requirement for Smad4in the extra-embryonic lineages; however, within the embryo proper,characterization of the specific roles of Smad4 during gastrulation and lineage specification remains limited. We have employed a Smad4conditional allele to specifically inactivate the Smad4 gene in the early mouse epiblast. Loss of Smad4 in this tissue results in a profound failure to pattern derivatives of the anterior primitive streak, such as prechordal plate, node, notochord and definitive endoderm. In contrast to these focal defects, many well-characterized TGFβ- and Bmp-regulated processes involved in mesoderm formation and patterning are surprisingly unaffected. Mutant embryos form abundant extra-embryonic mesoderm, including allantois, a rudimentary heart and middle primitive streak derivatives such as somites and lateral plate mesoderm. Thus, loss of Smad4 in the epiblast results not in global developmental abnormalities but instead in restricted patterning defects. These results suggest that Smad4 potentiates a subset of TGFβ-related signals during early embryonic development, but is dispensable for others.
Airborne Sound Level Difference between Dwellings at Low Frequencies
Authors: Gibbs B.M. , Maluski S.
Published: June 2004

This paper describes work on the relationship between laboratory measurements of the sound insulation of walls and floors, and the sound level difference between dwellings at frequencies below 200 Hz. The aim of the work was to describe the sound transmission between sound fields in small rooms and at low frequencies in terms of the modal characteristics of the spaces and of the intervening walls/floors. An experimentally validated finite element method (FEM) model was developed and a parametric survey conducted on the effects on sound level difference of construction, room/wall dimension and the absorption of surfaces and contents. The existing international standard ISO 140 gives a diffuse field correction to the sound reduction index, to give the level difference. This paper proposes a supplementary correction, which is a function of the low frequency characteristics of the separated rooms and of the walls/floors. In addition a statistical estimate is given of level difference for the range of likely conditions between dwellings for both heavyweight masonry walls and lightweight cavity walls.
Decay Processes in Rooms with Non-Diffuse Sound Fields Part I: Ceiling Treatment with Absorbing Material
Authors: Nilsson Erling
Published: June 2004

The decay process in rooms with non-diffuse sound fields was the subject of this investigation. A rectangular room with high absorption at the ceiling and low absorption at the walls and floor constituted the basic configuration for the study. Several alterations of the room were carried out, including changes of room dimensions and the type of ceiling absorber, also additional treatment with absorbent material. The effects of these alterations on the decay curves were analysed. In order to predict the gross features of the decay curves, a two-system Statistical Energy Analysis model was developed. The sound field was subdivided into a grazing and nongrazing part. The grazing part comprised modes with propagation direction almost parallel to the ‘principal’ surface (generally the absorbent ceiling). The nongrazing part comprised the oblique modes, of importance for the decay process. The angle dependent absorbent properties of the principal surface were taken into account when subdividing the sound field into a grazing and nongrazing part. Measured and calculated decay curves for different room configurations were compared.
The Additive Risk Model for Purchase Timing
Authors: Seetharaman P. B.
Published: June 2004

This paper proposes the Additive Risk Model (ARM), first used by Aalen (1980), to explain households' interpurchase times. Unlike the Proportional Hazard Model (PHM), first proposed by Cox (1972), the ARM incorporates the effects of covariates on the individual hazard function in an additive (as opposed to multiplicative) manner. While a large number of previous studies on interpurchase timing have dealt with the question of correctly specifying the parametric distribution for interpurchase times, no study has explicitly investigated the question of correctly specifying the effects of covariates in the model. This study looks at this issue.

We propose an ARM that is suitable for purchase-timing data, and compare its empirical performance to that of the PHM and the Accelerated Failure Time Model (AFTM) using scanner panel data on laundry detergents, paper towels, and toilet tissue. We find that the ARM not only estimates and validates the observed interpurchase times better than existing models, but also recovers a time-varying price elasticity and shows a high degree of robustness in the estimated covariate effects to alternative parametric specifications of the baseline hazard. The estimates of covariate parameters under the PHM, on the other hand, are highly sensitive to alternative parametric specifications of the baseline hazard.
Implications of Reduced Search Cost and Free Riding in E-Commerce
Authors: Wu Dazhong , Ray Gautam , Geng Xianjun , Whinston Andrew
Published: June 2004

This paper examines a market where the provision of information service is costly, but information service has the characteristics of a public good. Consumers, on the other hand, can use the information service to make an informed purchase decision and derive higher utility from consuming their ideal product. However, after receiving the information service from an information service provider, consumers can easily free ride by purchasing at low-price sellers who do not provide any information service. The paper examines the competition where sellers compete by providing information service for horizontally differentiated products and where technology reduces consumers' search cost. It is found that in this market a seller needs to establish itself as an information service provider in order to make positive profits, even when there is free riding. A seller, however, cannot make positive profits by free riding all the time. Also, with an increase in competition in the information service market, sellers have reduced incentives to provide information service. It is also found that in this market a decrease in search cost may increase or decrease social welfare.
Growing, Growing, Gone: Cascades, Diffusion, and Turning Points in the Product Life Cycle
Authors: Golder Peter N. , Tellis Gerard J.
Published: June 2004

Research on the product life cycle (PLC) has focused primarily on the role of diffusion. This study takes a broader theoretical perspective on the PLC by incorporating informational cascades and developing and testing many new hypotheses based on this theory. On average, across 30 product categories, the authors find that: (i) New consumer durables have a typical pattern of rapid growth of 45% per year over 8 years. (ii) This period of growth is followed by a slowdown when sales decline by 15% and stay below those of the previous peak for 5 years. (iii) Slowdown occurs at 34% population penetration and about 50% of ultimate market penetration. (iv) Products with large sales increases at takeoff tend to have larger sales declines at slowdown. (v) Leisure-enhancing products tend to have higher growth rates and shorter growth stages than nonleisure-enhancing products. Time-saving products tend to have lower growth rates and longer growth stages than nontime-saving products. (vi) Lower probability of slowdown is associated with steeper price reductions, lower penetration, and higher economic growth. (vii) A hazard model can provide reasonable predictions of the slowdown as early as the takeoff.

The authors discuss the implications of these findings.
Research in Primary Oral Healthcare. Where have we Been? Where are we Going?
Authors: Eaton Kenneth
Published: June 2004

Key aims of the Faculty of General Dental Practitioners (UK) include promoting research in primary dental care and helping members to develop research skills. Progress in achieving these aims has been slow. Two major barriers—lack of relevant skills and finance—have been cited in the past;1,2 however, in the 1990s primary dental care was selected by the Department of Health as one of ten topics for specific funding within the national research and development (R&D) programme. For many years a small number of general dental practitioners (GDPs) have undertaken research projects as part of a master's or (for a very small number) doctorate degree, and have acquired research skills. Invariably they have suffered loss of practice income in the process. More recently, there have been opportunities such as the NHS Researcher Development Award3 for GDPs to acquire research skills without any loss of income. Furthermore, the increasing emphasis on the provision of evidence-based care founded on robust and relevant research and the changes in the system for the provision of primary oral healthcare within the NHS should provide new research opportunities for GDPs to take part in research without financial loss.
Cardiac Troponin T for Prediction of Short- and Long-Term Morbidity and Mortality after Elective Open Heart Surgery
Authors: Lehrke Stephanie , Steen Henning , Sievers Hans H , Peters Hanno , Opitz Armin , Müller-Bardorff Margit , Wiegand Uwe K H , Katus Hugo A , Giannitsis Evangelos
Published: June 2004

Background: Increased cardiac troponins in blood are observed after virtually every open heart surgery, indicating perioperative myocardial cell injury. We sought to determine the optimum time point for blood sampling and the respective cutoff value of cardiac troponin T (cTnT) for risk assessment in patients undergoing cardiac surgery.

Methods: In a series of 204 patients undergoing scheduled open heart surgery, mainly for coronary artery bypass grafting (n = 132) or valve repair (n = 27), cTnT concentrations were measured before and 4 and 8 h after cross-clamping and then daily for 7 days. Individual risk was assessed by use of the Cleveland Clinic Foundation Risk score and intraoperative risk indicators such as duration of cardiopulmonary bypass, cross-clamping, and perioperative release of cardiac markers. Patients were followed for 28 months.

Results: Cardiac mortality, all-cause mortality rates, and rates of nonfatal acute myocardial infarction (AMI) at 28 months were 6.9%, 8.8%, and 6.8%, respectively. cTnT was higher in patients with Q-wave AMI or postoperative heart failure requiring inotropic support, and in nonsurvivors. The ROC curve revealed a cTnT ≥0.46 μg/L at 48 h as the optimum discriminator for long-term cardiac mortality. Stepwise logistic regression identified higher Cleveland Clinic Risk Score [odds ratio (OR) = 2.6 per point], cross-clamp time >65 min (OR = 6.6), and cTnT (OR = 4.9) as significant and independent predictors of long-term cardiac mortality.

Conclusions: A single postoperative cTnT measurement can be used to estimate myocardial cell injury that impacts long-term survival after open heart surgery. It adds independently to established risk indicators.
What Do Feminist Theories Have to Offer to Literacy, Education, and Research?
Authors: Commeyras Michelle , Orellana Marjorie Faulstich , Bruce Bertram C. , Neilsen Lorri
Published: June 2004

The authors share how feminist theories affect their own work and explore the influence of feminist methodologies on classroom research.
Literacy Research That Makes a Difference
Authors: Shanahan Timothy , Neuman Susan B.
Published: June 2004

Which studies have changed how we teach literacy? What are the fundamental characteristics of studies that make a difference? The authors offer a conversation on these topics, and propose a list of 13 studies that have influenced instructional practice. [This article is reprinted in Preparing Reading Professionals. www.reading.orgpublicationsbbvbooksbk564]
Questions of Balance
Authors: Moore David W.
Published: June 2004

Book reviewed in this article:

The First R: Every Child's Right to Read. Edited by Michael F. Graves, Paul van den Broek, and Barbara M. Taylor. 1996.
Constructing School Success in Literacy: The Pathway to College Entrance for Minority Students
Authors: Bean Thomas W. , Valerio Paul Cantú
Published: June 2004

Book reviewed in this article:

Constructing School Success: The Consequences of Untracking Low‐Achieving Students. By Hugh Mehan, Irene Villanueva, Lea Hubbard, and Angela Lintz. 1996.
Revisiting the First‐Grade Studies: The Importance of Literacy History
Authors: Readence John E. , Barone Diane M.
Published: June 2004

The authors, editors of RRQ at the time of this publication, explaining why they have reprinted “The First‐Grade Studies” in this issue (see http:dx.doi.org10.1598RRQ.32.4.4) and their views of the lasting importance of Bond and Dykstra's research to the field.
Locating the Social and Political in Secondary School Literacy
Authors: Hinchman Kathleen A. , Moje Elizabeth B.
Published: June 2004

The authors suggest a number of possible futures for research on adolescent literacy issues. They emphasize the importance of the social and political with respect to the teaching and learning of older students, and pose numerous questions for those working in this shifting field.
Concurrent and Longitudinal Predictors of Reading: The Role of Metalinguistic and Short‐Term Memory Skills
Authors: Muter Valerie , Snowling Margaret
Published: June 2004

ABSTRACTS

The relationship between phonological awareness, short‐term memory, grammatical awareness, and reading accuracy was investigated in a follow‐up study of 34 9‐year‐olds originally studied as preschoolers. The best concurrent predictor set for reading accuracy at age 9 was grammatic knowledge, phoneme awareness, and speech rate, which together explained nearly 90% of the variance in reading skill. Phoneme deletion, nonword repetition, and letter knowledge measures taken at ages 5 and 6 predicted reading skill at age 9, while rhyme awareness proved a poor long‐term predictor.

SE INVESTIGÓ la relación entre la conciencia fonológica, la memoria a corto plazo, la conciencia gramatical y la precisión en lectura en un estudio de seguimiento de 34 niños de 9 años estudiados originalmente como preescolares. El mejor conjunto de predictores concurrentes de la precisión en lectura a los 9 años fue el conocimiento gramatical, la conciencia fonológica y la velocidad del habla, los que explicaron casi el 90% de la varianza en habilidad de lectura. Las medidas de supresión de fonemas, repetición de pseudopalabras y conocimiento de las letras, tomadas a los 5 y 6 años predijeron la habilidad de lectura a los 9 años, en tanto que la sensibilidad a las rimas resultó un predictor pobre a largo plazo.

DIE BEZIEHUNG zwischen phonologischem Bewußtsein, dem Kurzzeit‐Gedächtnis, grammatikalischer Erkenntnis und der Lesegenauigkeit wurde in einer Nachfolgestudie mit 34 Neunjährigen untersucht, welche ursprünglich als Vorschüler bereits beobachtet wurden. Die besten übereinstimmenden Vorhersagen, welche für die Lesegenauigkeit mit Erreichen des Alters von 9 Jahren festgesetzt wurden, waren grammatikalisches Wissen, phonemes Bewußtsein und die Aussprache‐Bemessung, welche zusammengenommen nahezu 90% der Abweichung bei der Lesefertigkeit erklärte. Phonemische Auslassungen, Silbenwiederholungen und Buchstabierkenntnisse als Bemessungen im Alter von 5 und 6 dienten zu Voraussagen über Leseleistungen im Alter von 9, während Rythmus‐Bewußtsein sich als schwacher Langzeit‐Vorhersagefaktor erwies.

ON A examiné la relation entre conscience phonologique, mémoire à court terme, conscience grammaticale, et maîtrise de la lecture dans une étude longitudinale portant sur 34 enfants de 9 ans suivis depuis l'école maternelle. Le meilleur ensemble de prédicteurs simultanés pour la lecture à l'âge de 9 ans a été la connaissance de la grammaire, la conscience phonémique, et la maîtrise du langage qui en semble rendent compte de 90% de la variance du savoir‐lire. Les évaluations de suppression de phonèmes, répétition de non‐mots, et connaissance des lettres effectuées à 5 et 6 ans ont permis de prévoir le niveau de lecture à l'âge de 9 ans, tandis que la conscience de la rime s'est révélée être un mauvais prédicteur à long terme.
Literacy on the Margins of the American Past
Authors: Weber Rose‐Marie
Published: June 2004

Book reviewed in this article:

Literacy, Education, and Society in New Mexico, 1693–1821. By Bernardo P. Gallegos. 1992.

“When I Can Read My Title Clear”: Literacy, Slavery, and Religion in the Antebellum South. By Janet Duitsman Cornelius. 1991.

Intimate Practices: Literacy and Cultural Work in U.S. Women's Clubs, 1880–1920. By Anne Ruggles Gere. 1997.
Portfolios: Assumptions, Tensions, and Possibilities
Authors: Tierney Robert J. , Clark Caroline , Fenner Linda , Herter Roberta J. , Simpson Carolyn Staunton , Wiser Bert
Published: June 2004

The authors discuss the history, theory, and research around the use of portfolios, emphasizing particularly practical implications for and implementation in the classroom.
Questions Teachers Ask About Spelling
Authors: Templeton Shane , Morris Darrell
Published: June 2004

Questions teachers frequently ask about spelling and spelling instruction, including how students learn to spell and which instructional methods are most effective, are addressed.
Teaching Literature to Adolescents
Authors: Lewis Cynthia
Published: June 2004

Book reviewed in this article:

On the Brink: Negotiating Literature and Life With Adolescents. By Susan Hynds. 1997.

Reading Across Cultures: Teaching Literature in a Diverse Society. Edited by Theresa Rogers and Anna O. Soter. 1997.

Authorizing Readers: Resistance and Respect in the Teaching of Literature. By Peter J. Rabinowitz and Michael W. Smith. 1998.

Knowledge in the Making: Challenging the Text in the Classroom. Edited by Bill Corcoran, Mike Hayhoe, and Gordon M. Pradl. 1994.
Negotiating the Multiple Realities of Technology in Literacy Research and Instruction
Authors: Labbo Linda D. , Reinking David
Published: June 2004

The authors consider the relation between research and practice as it applies to digital technologies. They do so within the multiple realities of different theoretical and methodological perspectives.
How Will Literacy Be Defined in the New Millennium?
Authors: Cunningham James W. , Many Joyce E. , Carver Ronald P. , Gunderson Lee , Mosenthal Peter B.
Published: June 2004

In this “RRQ Snippet,” five literacy researchers offer their insights in answering the title question. Topics including the influence of technology, standards, and classroom and student diversity are discussed.
How Will Literacy Be Assessed in the Next Millennium?
Authors: Tierney Robert J. , Moore David W. , Valencia Sheila W. , Johnston Peter
Published: June 2004

In this “RRQ Snippet,” several researchers share their ideas about trends in literacy assessment, including high‐stakes testing, the influence of technology, and assessment to inform instructional practice.
What Will Be the Influences of Media on Literacy in the Next Millennium?
Authors: Neuman Susan B. , Smagorinsky Peter , Enciso Patricia E. , Baldwin R. Scott , Hartman Douglas K.
Published: June 2004

In this “RRQ Snippet,” several literacy researchers discusses their ideas about how media, popular culture, and digital and new literacies will affect literacy teaching and learning in the near future.
What Will Be the Demands of Literacy in the Workplace in the Next Millennium?
Authors: Smith M Cecil , Mikulecky Larry , Kibby Michael W. , Dreher Mariam Jean , Dole Janice A.
Published: June 2004

In this “RRQ Snippet,” the authors discuss their ideas about the changing demands for today's—and tomorrow's—literate workforce.
How Will Diversity Affect Literacy in the Next Millennium?
Authors: McCarthey Sarah , Dressman Mark , Smolkin Laura , McGill‐Franzen Anne , Harris Violet J.
Published: June 2004

The authors discuss their ideas about the affect of diverse learners, classrooms, and societies on literacy teaching and learning.
Access to Print in Low‐Income and Middle‐Income Communities: An Ecological Study of Four Neighborhoods
Authors: Neuman Susan B. , Celano Donna
Published: June 2004

ABSTRACTS

Building on a growing body of ecological research, this study examines access to print in two low‐income and two middle‐income neighborhood communities in a large industrial city. It documents the availability of print in these communities, focusing on resources considered to be influential in a child's beginning development as a writer and reader. It describes the likelihood that children will find books and other resources, see signs, labels, and logos, public places (spaces) conducive to reading, books in local preschools, school libraries, and public library branches. Results of the year‐long analysis indicated striking differences between neighborhoods of differing income in access to print at all levels of analyses, with middle‐income children having a large variety of resources to choose from, while low‐income children having to rely on public institutions which provide unequal resources across communities. Such differences in access to print resources may have important implications for children's early literacy development.
The Role of Knowledge in Early Literacy
Authors: Neuman Susan B.
Published: June 2004

Book reviewed in this article:

Beating the Odds in Teaching All Children to Read. By Barbara Taylor, P. David Pearson, Kathleen Clark, and Sharon Walpole. September 30, 1999.

The Contexts of Comprehension: Information Book Read Alouds and Comprehension Acquisition. By Laura Smolkin and Carol Donovan. June 30, 2000.

The Interplay of Firsthand and Text‐Based Investigations in Science Education. By Annemarie Sullivan Palincsar and Shirley Magnusson. March 31, 2000.

The Scarcity of Informational Text in First Grade. By Nell Duke. August 31, 1999.
“Sounding American”: The consequences of new reforms on English language learners
Authors: Gutiérrez Kris D. , Asato Jolynn , Pacheco Mariana , Moll Luis C. , Olson Kathryn , Horng Eileen Lai , Ruiz Richard , García Eugene , McCarty Teresa L.
Published: June 2004

The authors highlight the omission of English language learners and their unique needs from reports such as that of the U.S. National Reading Panel. Situating their conversation in a sociocultural and socioeconomic context, they discuss how schools can and should help all children.
In Other Words: Translating or “Para‐Phrasing” as a Family Literacy Practice in Immigrant Households
Authors: ORELLANA MARJORIE FAULSTICH , REYNOLDS JENNIFER , DORNER LISA , MEZA MARÍA
Published: June 2004

ABSTRACTS

In this article we report on ethnographic research that explores the range of ways in which Spanish‐English bilingual immigrant youth interpret English language texts for their families. Drawing on participant observation in the homes and classrooms of 18 young adolescents who serve as interpreters for their families, 86 transcripts of theseinterpreters' oral Spanish translations of English texts, and 95 journal entries written by the youth about their translating experiences, we document the multiple literacies of daily life that youth engage in while translating or “para‐phrasing” for their families. We focus on interpretations of written text for close family members, done at home, and chart the domains of these multiple literacies. Using an activity setting/interactional analysis, we then examine how two home “para‐phrasing” events unfold and contrast these with activity settings for literacy learning in school. This largely unexplored literacy practice is a common one in immigrant households, and we argue that bilingual youth's experiences as cross‐language “para‐phrasers” can be used to support the within‐language paraphrasing that is an important part of school literacy practices.