bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary of the Delft University Wind Turbine Dedicated Airfoils
Authors: Timmer W. A. , van Rooij R. P. J. O. M.
Published: November 2003

This paper gives an overview of the design and wind tunnel test results of the wind turbine dedicated airfoils developed by Delft University of Technology (DUT). The DU-airfoils range in maximum relative thickness from 15% to 40% chord. The first designs were made with the XFOIL code. The computer program RFOIL, which is a modified version of XFOIL featuring an improved prediction around the maximum lift coefficient and the capability of predicting the effect of rotation on airfoil characteristics, has been used to design the airfoils since 1995. The measured effect of Gurney flaps, trailing edge wedges, vortex generators (vg) and trip wires on the airfoil characteristics of various DU-airfoils is presented. Furthermore, a relation between the thickness of the airfoil leading edge and the angle-of-attack for leading edge separation is given.
Blade-Wake Interaction Noise for Turbines With Downwind Rotors
Authors: McNerney G. M. , van Dam C. P. , Yen-Nakafuji D. T.
Published: November 2003

The interaction between the rotor and the tower wake is an important source of noise for wind turbines with downwind rotors. The tower wake modifies the dynamic pressure and the local flow incidence angle as seen by the blades and, hence, modifies the aerodynamic loading of the blade during blade passage. The resulting n per revolution fluctuation in the blade loading (where n is the number of blades) is the source of low frequency but potentially high amplitude sound levels. The Wind Turbine Company (WTC) Proof of Concept 250 kW (POC) wind turbine has been observed by field personnel to produce low-frequency emissions at the National Wind Technology Center (NWTC) site during specific atmospheric conditions. Consequently, WTC is conducting a three-phase program to characterize the low frequency emissions of its two-bladed wind turbines and to develop noise mitigation techniques if needed. This paper summarizes the first phase of this program including recent low-frequency noise measurements conducted on the WTC POC250 kW wind turbine, a review of the wake characteristics of circular towers as they pertain to the blade-wake interaction problem, and techniques to attenuate the sound pressure levels caused by the blade-wake interaction.
Statistical Analysis of Wind Turbine Inflow and Structural Response Data from the LIST Program
Authors: Nelson Luke D. , Manuel Lance , Sutherland Herbert J. , Veers Paul S.
Published: November 2003

The Long-Term Inflow and Structural Test (LIST) program is gathering inflow and structural response data on a modified version of the Micon 65/13 wind turbine at a test site near Bushland, Texas. Data from 491 ten-minute time data records are analyzed here to determine the dependency of fatigue and extreme loads on inflow parameters. Flap and edge bending moment ranges at a blade root are chosen as the structural response variable, z. Various parameters related to the inflow (including, for example, primary parameters such as the mean and standard deviation of the hub-height horizontal wind speed, and secondary parameters such as Reynolds stresses, vertical shear exponent, etc.) are each considered in an inflow parameter vector, x. Time series for the structural response, z, are processed in order to obtain a structural response parameter, y, where in separate statistical studies, y is taken to be either an equivalent fatigue load or an extreme load. This study describes a procedure by which the important “dependencies” of y on the various variables contained in the inflow parameter vector, x, may be determined considering all the available data. These dependencies of y on x are then recomputed using only the data with above-rated mean wind speeds (taken to be approximately 13 m/s). The procedure employed is similar to other studies, but we do not bin the data sets by wind speed since dependencies in one wind speed bin may be different from those in other bins. Also, our procedure, in sharp contrast to previous studies, examines each inflow parameter in the vector, x, in a sequential analysis, rather than by using multivariate regression. Results from the present study suggest that the primary inflow parameters have a small amount of predictive power in establishing fatigue and extreme loads. In addition, large correlations that exist between several of the secondary parameters individually and each of the primary parameters make it difficult for the secondary parameters to provide any additional explanation of turbine response once the primary parameters have been accounted for.
Disturbance Tracking Control and Blade Load Mitigation for Variable-Speed Wind Turbines
Authors: Stol Karl A.
Published: November 2003

A composite linear state-space controller was developed for a multi-objective problem in the variable-speed operation of wind turbines. Disturbance Tracking Control theory was applied to the design of a torque controller to optimize energy capture under the influence of persistent wind disturbances. A limitation in the theory for common multi-state models is described; this led to the design of a complementary pitch controller. The goal of the independent blade pitch design was to minimize blade root fatigue loads. A SymDyn model of a two-bladed, 600-kW machine was used for the simulation studies. Results indicate a 24% reduction in blade fatigue damage using the proposed controllers, compared to a conventional torque-only design. However, energy capture was not improved as much as expected, partly due to nonlinearity effects degrading the performance of the state-space estimator design. Tower base fatigue damage was shown to decrease significantly using active pitch.
Aerodynamic Analysis of Blunt Trailing Edge Airfoils
Authors: Standish K. J. , van Dam C. P.
Published: November 2003

The adoption of blunt trailing edge airfoils for the inboard region of large wind turbine blades has been proposed. Blunt trailing edge airfoils would not only provide a number of structural benefits, such as increased structural volume and ease of fabrication and handling, but they have also been found to improve the lift characteristics of airfoils. Therefore, the incorporation of blunt trailing edge airfoils would allow blade designers to more freely address the structural demands without having to sacrifice aerodynamic performance. Limited experimental data make it difficult for wind turbine designers to consider and conduct tradeoff studies using these section shapes and has provided the impetus for the present analysis of blunt trailing edge airfoils using computational fluid dynamics. Several computational techniques are applied, including a viscous/inviscid interaction method and three Reynolds-averaged Navier-Stokes methods.
Performance of an H-Darrieus in the Skewed Flow on a Roof1
Authors: Mertens Sander , van Kuik Gijs , van Bussel Gerard
Published: November 2003

Application of wind turbines on roofs of higher buildings is a subject of increasing interest. However, the wind conditions at the roof are complex and suitable wind turbines for this application are not yet developed. This paper addresses both issues: the wind conditions on the roof and the behavior of a roof-located wind turbine with respect to optimized energy yield. Vertical Axis Wind Turbines (VAWTs) are to be preferred for operation in a complex wind environment as is found on top of a roof. Since the wind vector at a roof is not horizontal, wind turbines on a roof operate in skewed flow. Thus the behavior of an H-Darrieus (VAWT) is studied in skewed flow condition. Measurements showed that the H-Darrieus produces an increased power output in skewed flow. The measurements are compared with a model based on Blade Element Momentum theory that also shows this increased power output. This in contradiction to a HAWT in skewed flow which suffers from a power decrease. The paper thus concludes that due to this property an H-Darrieus is preferred above the HAWT for operation on a flat roof of higher buildings.
Alternative Composite Materials for Megawatt-Scale Wind Turbine Blades: Design Considerations and Recommended Testing
Authors: Griffin Dayton A. , Ashwill Thomas D.
Published: November 2003

As part of the U.S. Department of Energy’s Wind Partnerships for Advanced Component Technologies program, Global Energy Concepts LLC (GEC) is performing a study concerning blades for wind turbines in the multi-megawatt range. Earlier in this project constraints to cost-effective scaling-up of the current commercial blade designs and manufacturing methods were identified, and candidate innovations in composite materials, manufacturing processes and structural configurations were assessed. In the present work, preliminary structural designs are developed for hybrid carbon fiber/fiberglass blades at system ratings of 3.0 and 5.0 MW. Structural performance is evaluated for various arrangements of the carbon blade spar, and critical performance aspects of the carbon material and blade structure are discussed. Recommendations are made for new testing of composite coupons and blade sub-structure to address the technical uncertainties identified in this work.
Numerical Implications of Solidity and Blade Number on Rotor Performance of Horizontal-Axis Wind Turbines
Authors: Duquette Matthew M. , Visser Kenneth D.
Published: November 2003

A numerical study was conducted to examine the impact of rotor solidity and blade number on the aerodynamic performance of small wind turbines. Blade element momentum theory and lifting line based wake theory were utilized to parametrically assess the effects of blade number and solidity on rotor performance. Increasing the solidity beyond what is traditionally used for electric generating wind turbines led to increased power coefficients at lower tip speed ratios, with an optimum between 3 and 4. An increase in the blade number at a given solidity also increased the maximum Cp for all cases examined. The possibility of a higher aerodynamic power extraction from solidity or blade number increases could lead to a higher overall system power production. Additional advantages over current 5% to 7% solidity, high speed designs would include lower noise, lower cut-in wind speed, and less blade erosion.
Wind Shear and Turbulence Effects on Rotor Fatigue and Loads Control
Authors: Eggers, A. J. , Digumarthi R. , Chaney K.
Published: November 2003

The effects of wind shear and turbulence on rotor fatigue and loads control are explored for a large horizontal axis wind turbine in variable speed operation at wind speeds from 4 to 20 m/s. Two- and three-blade rigid rotors are considered over a range of wind shear exponents up to 1.25 and a range of turbulence intensities up to 17%. RMS blade root flatwise moments are predicted to be very substantially increased at higher wind shear, and resultant fatigue damage is increased by many orders of magnitude. Smaller but similar trends occur with increasing turbulence levels. In-plane fatigue damage is driven by 1P gravity loads and exacerbated by turbulence level at higher wind speeds. This damage is higher by one to two orders of magnitude at the roots of the three-blade rotor compared with the two-blade rotor. Individual blade pitch control of fluctuating flatwise moments markedly reduces flatwise fatigue damage due to this source, and, to a lesser degree, the in-plane damage due to turbulence. The same is true of fluctuating rotor torque moments driven by turbulence and transmitted to the drive train. Blade root moments out of the plane of rotation aggregate to create rotor pitching and yawing moments transmitted to the turbine structure through the drive train to the yaw drive system and the tower. These moments are predicted to be relatively insensitive to turbulence level and essentially proportional to the wind shear exponent for the two-blade rotor. Fluctuating moments are substantially reduced with individual blade pitch control, and addition of a teeter degree-of-freedom should further contribute to this end. Fluctuating pitching and yawing moments of the three-blade rotor are substantially less sensitive to wind shear, more sensitive to turbulence level, and substantially lower than those for the two-blade rotor. Mean rotor torque and, hence, power are essentially the same for both rotors, independent of wind shear, and are somewhat reduced with individual blade pitch control of fluctuating flatwise moments. The same is true of mean rotor thrust; however fluctuations in rotor thrust are substantially reduced with individual blade pitch control.
Notch-Mediated Restoration of Regenerative Potential to Aged Muscle
Authors: Conboy Irina M. , Conboy Michael J. , Smythe Gayle M. , Rando Thomas A.
Published: November 2003

A hallmark of aging is diminished regenerative potential of tissues, but the mechanism of this decline is unknown. Analysis of injured muscle revealed that, with age, resident precursor cells (satellite cells) had a markedly impaired propensity to proliferate and to produce myoblasts necessary for muscle regeneration. This was due to insufficient up-regulation of the Notch ligand Delta and, thus, diminished activation of Notch in aged, regenerating muscle. Inhibition of Notch impaired regeneration of young muscle, whereas forced activation of Notch restored regenerative potential to old muscle. Thus, Notch signaling is a key determinant of muscle regenerative potential that declines with age.
Phosphatidylserine Receptor Is Required for Clearance of Apoptotic Cells
Authors: Li Ming O. , Sarkisian Matthew R. , Mehal Wajahat Z. , Rakic Pasko , Flavell Richard A.
Published: November 2003

Cells undergoing apoptosis during development are removed by phagocytes, but the underlying mechanisms of this process are not fully understood. Phagocytes lacking the phosphatidylserine receptor (PSR) were defective in removing apoptotic cells. Consequently, in PSR-deficient mice, dead cells accumulated in the lung and brain, causing abnormal development and leading to neonatal lethality. A fraction of PSR knockout mice manifested a hyperplasic brain phenotype resembling that of mice deficient in the cell death–associated genes encoding Apaf-1, caspase-3, and caspase-9, which suggests that phagocytes may also be involved in promoting apoptosis. These data demonstrate a critical role for PSR in early stages of mammalian organogenesis and suggest that this receptor may be involved in respiratory distress syndromes and congenital brain malformations.
Cell Corpse Engulfment Mediated by
C. elegans
Phosphatidylserine Receptor Through CED-5 and CED-12
Authors: Wang Xiaochen , Wu Yi-Chun , Fadok Valerie A. , Lee Ming-Chia , Gengyo-Ando Keiko , Cheng Li-Chun , Ledwich Duncan , Hsu Pei-Ken , Chen Jia-Yun , Chou Bin-Kuan , Henson Peter , Mitani Shohei , Xue Ding
Published: November 2003

During apoptosis, phosphatidylserine, which is normally restricted to the inner leaflet of the plasma membrane, is exposed on the surface of apoptotic cells and has been suggested to act as an “eat-me” signal to trigger phagocytosis. It is unclear how phagocytes recognize phosphatidylserine. Recently, a putative phosphatidylserine receptor (PSR) was identified and proposed to mediate recognition of phosphatidylserine and phagocytosis. We report that
psr-1
, the
Caenorhabditis elegans
homolog of PSR, is important for cell corpse engulfment. In vitro PSR-1 binds preferentially phosphatidylserine or cells with exposed phosphatidylserine. In
C. elegans
, PSR-1 acts in the same cell corpse engulfment pathway mediated by intracellular signaling molecules CED-2 (homologous to the human CrkII protein), CED-5 (DOCK180), CED-10 (Rac GTPase), and CED-12 (ELMO), possibly through direct interaction with CED-5 and CED-12. Our findings suggest that PSR-1 is likely an upstream receptor for the signaling pathway containing CED-2, CED-5, CED-10, and CED-12 proteins and plays an important role in recognizing phosphatidylserine during phagocytosis.
High Deleterious Genomic Mutation Rate in Stationary Phase of
Escherichia coli
Authors: Loewe Laurence , Textor Volker , Scherer Siegfried
Published: November 2003

In natural habitats, bacteria spend most of their time in some form of growth arrest. Little is known about deleterious mutations in such stages, and consequently there is limited understanding of what evolutionary events occur. In a deleterious mutation accumulation experiment in prolonged stationary phase of
Escherichia coli
, about 0.03 slightly deleterious mutations were observed per genome per day. This is over an order of magnitude higher than extrapolations from fast-growing cells, but in line with inferences from observations in adaptive stationary phase mutation experiments. These findings may affect understanding of bacterial evolution and the emergence of bacterial pathogenicity.
Fish Exploiting Vortices Decrease Muscle Activity
Authors: Liao James C. , Beal David N. , Lauder George V. , Triantafyllou Michael S.
Published: November 2003

Fishes moving through turbulent flows or in formation are regularly exposed to vortices. Although animals living in fluid environments commonly capture energy from vortices, experimental data on the hydrodynamics and neural control of interactions between fish and vortices are lacking. We used quantitative flow visualization and electromyography to show that trout will adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments.
The Structure of Importin-ß Bound to SREBP-2: Nuclear Import of a Transcription Factor
Authors: Lee Soo Jae , Sekimoto Toshihiro , Yamashita Eiki , Nagoshi Emi , Nakagawa Atsushi , Imamoto Naoko , Yoshimura Masato , Sakai Hiroaki , Chong Khoon Tee , Tsukihara Tomitake , Yoneda Yoshihiro
Published: November 2003

The sterol regulatory element–binding protein 2 (SREBP-2), a nuclear transcription factor that is essential for cholesterol metabolism, enters the nucleus through a direct interaction of its helix-loop-helix leucine zipper domain with importin-β. We show the crystal structure of importin-β complexed with the active form of SREBP-2. Importin-β uses characteristic long helices like a pair of chopsticks to interact with an SREBP-2 dimer. Importin-β changes its conformation to reveal a pseudo-twofold symmetry on its surface structure so that it can accommodate a symmetric dimer molecule. Importin-β may use a similar strategy to recognize other dimeric cargoes.
Mutation of MEF2A in an Inherited Disorder with Features of Coronary Artery Disease
Authors: Wang Lejin , Fan Chun , Topol Sarah E. , Topol Eric J. , Wang Qing
Published: November 2003

The early genetic pathway(s) triggering the pathogenesis of coronary artery disease (CAD) and myocardial infarction (MI) remain largely unknown. Here, we describe an autosomal dominant form of CAD/MI (
adCAD1
) that is caused by the deletion of seven amino acids in transcription factor MEF2A. The deletion disrupts nuclear localization of MEF2A, reduces MEF2A-mediated transcription activation, and abolishes synergistic activation by MEF2A and by the transcription factor GATA-1 through a dominant-negative mechanism. The MEF2A protein demonstrates strong expression in the endothelium of coronary arteries. These results identify a pathogenic gene for a familial vascular disease with features of CAD and implicate the MEF2A signaling pathway in the pathogenesis of CAD/MI.
Observation of the Inverse Doppler Effect
Authors: Seddon N. , Bearpark T.
Published: November 2003

We report experimental observation of an inverse Doppler shift, in which the frequency of a wave is increased on reflection from a receding boundary. This counterintuitive effect has been produced by reflecting a wave from a moving discontinuity in an electrical transmission line. Doppler shifts produced by this system can be varied in a reproducible manner by electronic control of the transmission line and are typically five orders of magnitude greater than those produced by solid objects with kinematic velocities. Potential applications include the development of tunable and multifrequency radiation sources.
Water Isotope Ratios D/H,
18
O/
16
O, 17O/
16
O in and out of Clouds Map Dehydration Pathways
Authors: Webster Christopher R. , Heymsfield Andrew J.
Published: December 2003

Water isotope ratios have been measured by laser absorption spectroscopy in and out of cirrus clouds formed in situ and convectively generated in anvils over subtropical regions. Water vapor in the tropical and subtropical upper troposphere shows a wide range of isotopic depletion not observed previously. The range suggests that dehydration of upper tropospheric air occurs both by convective dehydration and by gradual dehydration mechanisms. Twenty-five percent of upper tropospheric water sampled is in ice particles whose isotopic signatures are used to identify those grown in situ from those lofted from below.
Global Freshwater Resources: Soft-Path Solutions for the 21st Century
Authors: Gleick Peter H.
Published: November 2003

Twentieth-century water policies relied on the construction of massive infrastructure in the form of dams, aqueducts, pipelines, and complex centralized treatment plants to meet human demands. These facilities brought tremendous benefits to billions of people, but they also had serious and often unanticipated social, economical, and ecological costs. Many unsolved water problems remain, and past approaches no longer seem sufficient. A transition is under way to a “soft path” that complements centralized physical infrastructure with lower cost community-scale systems, decentralized and open decision-making, water markets and equitable pricing, application of efficient technology, and environmental protection.
Modern Global Climate Change
Authors: Karl Thomas R. , Trenberth Kevin E.
Published: December 2003

Modern climate change is dominated by human influences, which are now large enough to exceed the bounds of natural variability. The main source of global climate change is human-induced changes in atmospheric composition. These perturbations primarily result from emissions associated with energy use, but on local and regional scales, urbanization and land use changes are also important. Although there has been progress in monitoring and understanding climate change, there remain many scientific, technical, and institutional impediments to precisely planning for, adapting to, and mitigating the effects of climate change. There is still considerable uncertainty about the rates of change that can be expected, but it is clear that these changes will be increasingly manifested in important and tangible ways, such as changes in extremes of temperature and precipitation, decreases in seasonal and perennial snow and ice extent, and sea level rise. Anthropogenic climate change is now likely to continue for many centuries. We are venturing into the unknown with climate, and its associated impacts could be quite disruptive.
Attosecond Synchronization of High-Harmonic Soft X-rays
Authors: Mairesse Y. , de Bohan A. , Frasinski L. J. , Merdji H. , Dinu L. C. , Monchicourt P. , Breger P. , Kovačev M. , Taïeb R. , Carré B. , Muller H. G. , Agostini P. , Salières P.
Published: November 2003

Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attoseconds in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter.
Are We Ready for Pandemic Influenza?
Authors: Webby Richard J. , Webster Robert G.
Published: November 2003

During the past year, the public has become keenly aware of the threat of emerging infectious diseases with the global spread of severe acute respiratory syndrome (SARS), the continuing threat of bioterrorism, the proliferation of West Nile virus, and the discovery of human cases of monkeypoxin the United States. At the same time, an old foe has again raised its head, reminding us that our worst nightmare may not be a new one. In 2003, highly pathogenic strains of avian influenza virus, including the H5N1 and H7N7 subtypes, again crossed from birds to humans and caused fatal disease. Direct avian-to-human influenza transmission was unknown before 1997. Have we responded to these threats by better preparing for emerging disease agents, or are we continuing to act only as crises arise? Here we consider progress to date in preparedness for an influenza pandemic and review what remains to be done. We conclude by prioritizing the remaining needs and exploring the reasons for our current lack of preparedness for an influenza pandemic.
Molecular Memories That Survive Silicon Device Processing and Real-World Operation
Authors: Liu Zhiming , Yasseri Amir A. , Lindsey Jonathan S. , Bocian David F.
Published: November 2003

If molecular components are to be used as functional elements in place of the semiconductor-based devices present in conventional microcircuitry, they must compete with semiconductors under the extreme conditions required for processing and operating a practical device. Herein, we demonstrate that porphyrin-based molecules bound to Si(100), which exhibit redox behavior useful for information storage, can meet this challenge. These molecular media in an inert atmosphere are stable under extremes of temperature (400°C) for extended periods (approaching 1 hour) and do not degrade under large numbers of read-write cycles (10
12
).
Oceanic Rossby Waves Acting As a "Hay Rake" for Ecosystem Floating By-Products
Authors: Dandonneau Yves , Vega Andres , Loisel Hubert , du Penhoat Yves , Menkes Christophe
Published: November 2003

Recent satellite observations of Rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave-induced upwelling could stimulate photosynthesis. Instead, we show that chlorophyll maxima are located in abnormally warm water, in Rossby wave–induced convergences. This excludes inputs of nutrients from deeper water. We argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by Rossby waves, acting as “marine hay rakes,” in convergence zones. Such processes may be determinant for the distribution of living organisms in oligotrophic areas.
Genetic Analysis of a High-Level Vancomycin-Resistant Isolate of
Staphylococcus aureus
Authors: Weigel Linda M. , Clewell Don B. , Gill Steven R. , Clark Nancye C. , McDougal Linda K. , Flannagan Susan E. , Kolonay James F. , Shetty Jyoti , Killgore George E. , Tenover Fred C.
Published: November 2003

Vancomycin is usually reserved for treatment of serious infections, including those caused by multidrug-resistant
Staphylococcus aureus
. A clinical isolate of
S. aureus
with high-level resistance to vancomycin (minimal inhibitory concentration = 1024 μg/ml) was isolated in June 2002. This isolate harbored a 57.9-kilobase multiresistance conjugative plasmid within which Tn
1546
(
vanA
) was integrated. Additional elements on the plasmid encoded resistance to trimethoprim (
dfrA
), β-lactams (
blaZ
), aminoglycosides (
aacA-aphD
), and disinfectants (
qacC
). Genetic analyses suggest that the long-anticipated transfer of vancomycin resistance to a methicillin-resistant
S. aureus
occurred in vivo by interspecies transfer of Tn
1546
from a co-isolate of
Enterococcus faecalis
.
Carbon in Amazon Forests: Unexpected Seasonal Fluxes and Disturbance-Induced Losses
Authors: Saleska Scott R. , Miller Scott D. , Matross Daniel M. , Goulden Michael L. , Wofsy Steven C. , da Rocha Humberto R. , de Camargo Plinio B. , Crill Patrick , Daube Bruce C. , de Freitas Helber C. , Hutyra Lucy , Keller Michael , Kirchhoff Volker , Menton Mary , Munger J. William , Pyle Elizabeth Hammond , Rice Amy H. , Silva Hudson
Published: November 2003

The net ecosystem exchange of carbon dioxide was measured by eddy covariance methods for 3 years in two old-growth forest sites near Santarém, Brazil. Carbon was lost in the wet season and gained in the dry season, which was opposite to the seasonal cycles of both tree growth and model predictions. The 3-year average carbon loss was 1.3 (confidence interval: 0.0 to 2.0) megagrams of carbon per hectare per year. Biometric observations confirmed the net loss but imply that it is a transient effect of recent disturbance superimposed on long-term balance. Given that episodic disturbances are characteristic of old-growth forests, it is likely that carbon sequestration is lower than has been inferred from recent eddy covariance studies at undisturbed sites.
Structure-Based Carbon Nanotube Sorting by Sequence-Dependent DNA Assembly
Authors: Zheng Ming , Jagota Anand , Strano Michael S. , Santos Adelina P. , Barone Paul , Chou S. Grace , Diner Bruce A. , Dresselhaus Mildred S. , Mclean Robert S. , Onoa G. Bibiana , Samsonidze Georgii G. , Semke Ellen D. , Usrey Monica , Walls Dennis J.
Published: November 2003

Wrapping of carbon nanotubes (CNTs) by single-stranded DNA (ssDNA) was found to be sequence-dependent. A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the smaller diameter and metallic tubes, whereas late fractions are enriched in the larger diameter and semiconducting tubes.
Energy Resources and Global Development
Authors: Chow Jeffrey , Kopp Raymond J. , Portney Paul R.
Published: November 2003

In order to address the economic and environmental consequences of our global energy system, we consider the availability and consumption of energy resources. Problems arise from our dependence on combustible fuels, the environmental risks associated with their extraction, and the environmental damage caused by their emissions. Yet no primary energy source, be it renewable or nonrenewable, is free of environmental or economic limitations. As developed and developing economies continue to grow, conversion to and adoption of environmentally benign energy technology will depend on political and economic realities.
Cell Migration: Integrating Signals from Front to Back
Authors: Ridley Anne J. , Schwartz Martin A. , Burridge Keith , Firtel Richard A. , Ginsberg Mark H. , Borisy Gary , Parsons J. Thomas , Horwitz Alan Rick
Published: December 2003

Cell migration is a highly integrated multistep process that orchestrates embryonic morphogenesis; contributes to tissue repair and regeneration; and drives disease progression in cancer, mental retardation, atherosclerosis, and arthritis. The migrating cell is highly polarized with complex regulatory pathways that spatially and temporally integrate its component processes. This review describes the mechanisms underlying the major steps of migration and the signaling pathways that regulate them, and outlines recent advances investigating the nature of polarity in migrating cells and the pathways that establish it.
Global Air Quality and Pollution
Authors: Akimoto Hajime
Published: December 2003

The impact of global air pollution on climate and the environment is a new focus in atmospheric science. Intercontinental transport and hemispheric air pollution by ozone jeopardize agricultural and natural ecosystems worldwide and have a strong effect on climate. Aerosols, which are spread globally but have a strong regional imbalance, change global climate through their direct and indirect effects on radiative forcing. In the 1990s, nitrogen oxide emissions from Asia surpassed those from North America and Europe and should continue to exceed them for decades. International initiatives to mitigate global air pollution require participation from both developed and developing countries.
Testing Theories for the Gender Difference
Authors: Rosser Sue V.
Published: November 2003

Women in Science
Career Processes and Outcomes. Yu Xie and Kimberlee A. Shauman. Harvard University Press, Cambridge, MA, 2003. 336 pp. $59.95, £38.95, €55.30. ISBN 0-674-01034-5.

In this comprehensive exploration of gender differences in science careers in the United States, the authors consider the trajectory from high school to graduate school to combining jobs with families. Analyzing 17 data sets, they consider how students are selected into and out of science education and how social forces shape choices in the science labor market.
Nota Bene: Spellbound
Authors: Smith Orla
Published: November 2003

Changing the Face of Medicine
Celebrating America's Women Physicians. Helen S. More and Manon Parry, Curators. National Library of Medicine, Bethesda, MD. Through 2 April 2005.
www.nlm.nih.gov/changingthefaceofmedicine

The exhibition and its accompanying Web site and DVDs highlight the inspirational stories of women who have influenced and enhanced the practice of medicine in the United States.
Chronic non-malignant musculoskeletal pain in older adults: clinical issues and opioid intervention
Authors: Podichetty V K , Mazanec D J , Biscup R S
Published: December 2003

Musculoskeletal pain is common, frequently under-reported, and inadequately treated in the older adult. The objective of this article is to review the management of musculoskeletal pain syndromes in older adults emphasising the potential role of opioid agents in carefully selected patients. Systematic analysis of the relevant literature was done. Even in cognitively impaired patients, assessment of musculoskeletal pain is mandatory. An algorithm for musculoskeletal pain is presented emphasising a stepwise pharmacological approach in combination with an array of non-pharmacological therapies. Comorbid conditions may limit therapeutic choices, particularly in the elderly. Repeated assessment of pain levels as well as functional status is critical for optimal pain management.
Genome size, heterochromatin organisation, and ribosomal gene mapping in four species of Ribes
Authors: Chiche Joëlle , Brown Spencer C , Leclerc Jean-Claude , Siljak-Yakovlev Sonja
Published: December 2003

Four wild Ribes species (Ribes alpinum L., Ribes petraeum Wulf., Ribes rubrum L., and Ribes uva- crispa L.; all 2n = 2x = 16) were surveyed for their chromosome and genome organisation. Their genome size was assessed using flow cytometry. Ribes alpinum had 5.3% more nuclear DNA than did the three other species, whose average was 2C = 1.91 pg with 40.4% GC. In addition, GC- and AT-rich heterochromatin and rDNA (18S5.8S26S and 5S) patterns were studied using fluorochrome banding and double-target fluorescence in situ hybridization (FISH), respectively. Only GC-rich heterochromatin was detected, co-localizing with 18S26S rDNA. Fluorochrome banding and FISH patterns revealed marked differences between species. Ribes alpinum and R. uva-crispa differed from R. rubrum and R. petraeum by the number of 18S26S sites and the localization of 5S rDNA. Ribes alpinum and R. uva-crispa were differentiated by the number of 5S sites. Ribes rubrum and R. petraeum also differed by the number of 5S sites and by the size of the GC-rich band on the satellite chromosome pair. These results should contribute to a better understanding of phylogenetic relationships among these species.Key words: Ribes, flow cytometry, fluorochrome banding, FISH, rDNA, NORs.
Transfer of material through the microspore exine  from the loculus into the cytoplasm
Authors: Rowley John R , Skvarla John J , El-Ghazaly Gamal
Published: December 2003

Our results and those we review indicate that the exine has a great capacity for modifications that enable nutrients to pass through from the anther loculus to the microspore cytoplasm. Avenues of passage include strands, some of which are viscin threads, from the tapetum to microspores in, for example, Betula, Fuchsia, and Epilobium. Micro channels in Lopezia, Gaura, and Gelsemium extend through the ectexine, endexine, and intine to the cytoplasm. The bulge regions in Epilobium represent portions of the endexine that become very greatly enlarged, forming conducting channels that transport materials into the microspore cytoplasm. Results with tracers such as colloidal iron and lanthanum have also shown that exines of microspores are permeable across areas lacking obvious channels.Key words: Betula, Epilobium, exine, Fuchsia, Gaura, Gelsemium, Lopezia, microchannels, pollen, tapetum, tufts, viscin threads.
Predispersal seed predation and population dynamics in the perennial understorey herb Actaea spicata
Authors: Fröborg Heléne , Eriksson Ove
Published: December 2003

Predispersal seed predation by a moth larva, Eupithecia immundata Leinig & Zeller (Geometridae), and its impact on population dynamics of the perennial herb Actaea spicata L. were studied during 7 years in deciduous and mixed coniferous forest populations in southeastern Sweden. Twelve population matrix models were constructed based on transition probabilities among six stage classes in the populations. The fraction of seeds consumed varied between 21% and 80% but was not significantly correlated with seed production. Experimental seed addition compensating for seed losses caused by the seed predator resulted in increased seedling emergence in one of the populations. Population growth rate was positive (λ > 1) in 1 of 6 years in the deciduous forest population and in 2 of 6 years in the mixed coniferous forest population. Survival among reproductive individuals contributed most strongly to λ in both populations. In some years, the projected λ changed from positive to negative values because of seed loss caused by E. immundata. However, results suggest that seed predation did not affect λ to any large extent, despite a considerable seed predation. This study is one of the rare efforts to estimate the impact of seed predation on population dynamics of perennial plants.Key words: Actaea spicata, demography, population dynamics, predispersal seed predation, seedling recruitment.
Ultrastructure of conidiogenesis and appendage ontogeny in the coelomyceteBartalinia robillardoides
Authors: Wong M KM , Jones E BG , Abdel-Wahab M A , Au D WT , Vrijmoed L LP
Published: December 2003

Conidiogenesis and conidial appendage ontogeny of the coelomycete Bartalinia robillardoides Tassi was studied at the light microscope, scanning electron microscope, and transmission electron microscope levels. Conidiogenesis in B. robillardoides is holoblastic. Appendage ontogeny begins as a cellular outgrowth of the apical and the basal cells of the young conidium, the former developing prior to the basal appendage. Conidia detach from the conidiogenous cells schizolytically. Mature conidial cell walls comprise two layers: an outer electron-dense layer, 3038 nm, and an inner less electron-dense layer, 100125 nm. The apical appendages arise from an outgrowth of the apical cell, which then branches to form the appendages. The single basal appendage arises from the junction between the basal cell of the conidium and the conidiogenous cell prior to conidial detachment from the conidiogenous cell, as an outgrowth of the conidial cell wall. Conidial appendage ontogeny is compared with those of other coelomycetes.Key words: Annellidic, appendage ontogeny, coelomycetes, holoblastic.
A PCR-RFLP marker distinguishing Ophiostoma clavigerum from morphologically similar Leptographium species associated with bark beetles
Authors: Lee Sangwon , Kim Jae-Jin , Fung Simon , Breuil Colette
Published: December 2003

Ophiostoma clavigerum, carried by Dendroctonus ponderosae and Dendroctonus jeffreyi, has morphological characteristics that are similar to other Ophiostoma and Leptographium species. The partial β-tubulin gene of 45 strains belonging to seven species was amplified by PCR and digested by the restriction enzyme HinfI. The specific restriction fragment length polymorphism obtained for O. clavigerum provided the means for its reliable identification. We are also reporting that O. clavigerum ascocarps have short necks; this fact has not been shown previously.Key words: Ophiostoma clavigerum, Leptographium, β-tubulin gene, RFLP, bark beetle.
Molecular diversity of the 5S rDNA units in theElymus dahuricuscomplex (Poaceae: Triticeae) supports the genomic constitution ofSt,Y, andHhaplomes
Authors: Baum Bernard R , Bailey L Grant , Johnson Douglas A , Agafonov Alex V
Published: December 2003

The phylogenetic analysis of 118 5S rRNA gene sequences cloned from members of the Elymus dahuricus complex containing the St, Y, and H haplomes, and of several related species containing at least one of these three haplomes, is reported. Differences in sequence pattern, primarily within the nontranscribed spacer, enabled the identification of six putative orthologous groups that we refer to as unit classes. In previous publications, we have been able to assign unit classes to haplomes. In addition to four unit classes previously identified in other genera, namely the long H1, long S1, long P1, and long {Y1, here we document two new unit classes called the long S2 and long W1. Most sequences of the E. dahuricus complex and related tetraploid species are classified as long S1 and assigned to the St haplome. Both long S1 and long S2 unit classes were identified in the diploid Pseudoroegneria spicata (Pursh) Á. Löve with the St haplome. The long S2 unit class was also identified in the hexaploid Elymus scabrus (R. Br.) Á. Löve with the St,Y,and W haplomes. The long P1 was known from the diploid Agropyron cristatum Gaertn. with the P haplome, and the long W1 was determined in Australopyrum retrofractum (Vickery) Á. Löve, known to contain the W haplome, but was not yet detected in E. scabrus, a hexaploid species with W being one of the three haplomes. The long H1 reported earlier from Hordeum was identified in several clones of the E. dahuricus complex. As previously reported, the long {Y1 unit class was found to be rare overall, but we identified it in a few clones of Elymus drobovii and in the E. dahuricus complex.Key words: 5S rDNA, unit classes, haplomes, concerted evolution.
The upland hardwood component of Prince Edward Island's remnant Acadian forest: determination of depth of edge and patterns of exotic plant invasion
Authors: MacQuarrie Kate , Lacroix Christian
Published: December 2003

The upland hardwood component of Prince Edward Island's Acadian forest is among the best remaining examples of the precolonial landscape, but it has been severely fragmented during the past 300 years of human use and settlement. Despite the ecological importance of this remnant habitat and its level of fragmentation, there has been no assessment of depth of edge or exotic plant invasion in these areas. Three 300 m long edgeinterior transects were established in each of six study sites. Nine 100-m2 circular plots were sampled along each transect at distances from 5.7 to 300 m; one external plot was established at each transect to sample species in adjacent habitats. In each plot, all vascular plants were identified, a visual estimate of percent cover was made, and soil temperature, canopy cover, and tree diameters were measured. An edgeinterior plant community gradient was found within these forests; a plant community characteristic of interior conditions was not reached until a distance of more than 120 m from an edge. This suggests that upland hardwood protected areas smaller than 240 m on a side (5.75 ha) are unlikely to include interior habitat, and sites should be greater than 320 m on all sides (10.24 ha) to ensure at least some interior habitat for vascular plants. Invasion by exotic species was found to be more extensive than that reported from other jurisdictions, and innermost (300 m) plots were not free from exotics. Fifteen exotic species were found within the study sites, with Veronica officinalis (common speedwell) and Hieracium lachenalii (hawkweed) being the most invasive, both in terms of distance penetrated and area covered.Key words: Acadian forest, fragmentation, depth of edge, protected area, Veronica, Hieracium.
Comparative flower structure of three species of sundew (Drosera anglica,Drosera linearis, andDrosera rotundifolia) in relation to breeding system
Authors: Murza Gillian L , Davis Arthur R
Published: December 2003

Whereas much attention has been given to the fascinating prey-trapping leaves of carnivorous plants, less research has been conducted on their flower structure and breeding systems. Accordingly, a comparative study of the floral morphology and anatomy of the three species of sundews (Droseraceae: Drosera anglica Huds., Drosera linearis Goldie, and Drosera rotundifolia L.) in Saskatchewan was performed to ascertain the presence of floral rewards for potential pollinators and to obtain pollen to ovule ratios, an indicator of breeding system. Utilizing light and scanning electron microscopy, differences between the three species were apparent in length of styles, number of placentas, anther and pollen colour, and structure of glandular trichomes on sepals. The occurrence of features unique to each species does not support the concept of D. anglica as a hybrid of the other two species. Flowers of all three species lack nectaries, although clusters of papillate cells that were reminiscent of secretory tissue were observed at the apices of anthers and at the summits of ovaries. Pollen to ovule ratios were low for all species, ranging from 9.0 to 18.7 in D. rotundifolia and D. linearis, respectively, suggesting an autogamous breeding system for each species.Key words: Drosera anglica, Drosera linearis, Drosera rotundifolia, Droseraceae, comparative flower structure, pollen to ovule ratios, breeding system.
Gamma aminobutyrate: from intellectual curiosity to practical pest control
Authors: Shelp Barry J , Van Cauwenberghe Owen R , Bown Alan W
Published: December 2003

The authors describe the development of gamma aminobutyrate (GABA) as a potential control agent in plant  invertebrate pest systems. The evidence indicates that GABA accumulation in plants in response to biotic and abiotic stresses is mediated via the activation of glutamate decarboxylase. More applied research, based on the fact that GABA acts as an inhibitory neurotransmitter in invertebrate pests, indicates that ingested GABA disrupts nerve functioning and causes damage to oblique-banded leafroller larvae, and that walking or herbivory by tobacco budworm and oblique-banded leafroller larvae stimulate GABA accumulation in soybean and tobacco, respectively. In addition, elevated levels of endogenous GABA in genetically engineered tobacco deter feeding by tobacco budworm larvae and infestation by the northern root-knot nematode. It is concluded that genetically engineered crop species overexpressing glutamate decarboxylase and having high GABA-producing potential may be an alternative strategy to chemical pesticides for the management of invertebrate pests.Key words: gamma aminobutyrate, glutamate decarboxylase, invertebrate pests, plant defense.