bluuebunny/crossref_metadata_2025 huggingface dataset:
Geometric Design Using Hypotrochoid and Nonundercutting Conditions for an Internal Cycloidal Gear
Authors: Hwang Yii-Wen , Hsieh Chiu-Fan
Published: March 2007

This paper uses the theory of gearing to derive the mathematical model of an internal cycloidal gear with tooth difference. Whereas the outer rotor profile is based on a curve equidistant to a hypotrochoidal (or extended hypocycloid) curve, the inner rotor design generally depends upon type of use—e.g., when used as a speed reducer, it is a pin wheel. Therefore, this analysis proposes designs for both a gerotor and a speed reducer. Specifically, for an inner rotor used as a gerotor pump, it outlines a mathematical model to improve pump efficiency and derives a dimensionless equation of nonundercutting. For the speed reducer, it develops and demonstrates with numerical examples, a feasible design region without undercutting on the tooth profile or interference between the adjacent pins.
Box Approximations of Planar Linkage Configuration Spaces
Authors: Porta J. M. , Ros L. , Creemers T. , Thomas F.
Published: March 2007

This paper presents a numerical method able to compute all possible configurations of planar linkages. The procedure is applicable to rigid linkages (i.e., those that can only adopt a finite number of configurations) and to mobile ones (i.e., those that exhibit a continuum of possible configurations). The method is based on the fact that this problem can be reduced to finding the roots of a polynomial system of linear, quadratic, and hyperbolic equations, which is here tackled with a new strategy exploiting its structure. The method is conceptually simple and easy to implement, yet it provides solutions of the desired accuracy in short computation times. Experiments are included that show its performance on the double butterfly linkage and on larger linkages formed by the concatenation of basic patterns.
Gene Co-Inheritance and Gene Transfer
Authors: Brandvain Yaniv , Barker Michael S. , Wade Michael J.
Published: March 2007

Functional transfer of mitochondrial genes to the nucleus is very common in some taxa but entirely lacking in others. Current evolutionary theories to account for this variation predict that outcrossing, which allows escape from Muller's ratchet and faster spread of beneficial mutations, should favor gene transfer. We find that functional gene transfer is more common in selfing or clonal plants than in outcrossing plants, a pattern opposite to prediction. We suggest that reproductive modes, such as selfing and vegetative reproduction, conserve adaptive mitonuclear gene combinations, allowing functional transfer, whereas outcrossing prevents transfer by breaking up these combinations.
Structure of Nup58/45 Suggests Flexible Nuclear Pore Diameter by Intermolecular Sliding
Authors: Melčák Ivo , Hoelz André , Blobel Günter
Published: March 2007

The nucleoporins Nup58 and Nup45 are part of the central transport channel of the nuclear pore complex, which is thought to have a flexible diameter. In the crystal structure of an α-helical region of mammalian Nup58/45, we identified distinct tetramers, each consisting of two antiparallel hairpin dimers. The intradimeric interface is hydrophobic, whereas dimer-dimer association occurs through large hydrophilic residues. These residues are laterally displaced in various tetramer conformations, which suggests an intermolecular sliding by 11 angstroms. We propose that circumferential sliding plays a role in adjusting the diameter of the central transport channel.
Bottom-Up Determination of Air-Sea Momentum Exchange Under a Major Tropical Cyclone
Authors: Jarosz Ewa , Mitchell Douglas A. , Wang David W. , Teague William J.
Published: March 2007

As a result of increasing frequency and intensity of tropical cyclones, an accurate forecasting of cyclone evolution and ocean response is becoming even more important to reduce threats to lives and property in coastal regions. To improve predictions, accurate evaluation of the air-sea momentum exchange is required. Using current observations recorded during a major tropical cyclone, we have estimated this momentum transfer from the ocean side of the air-sea interface, and we discuss it in terms of the drag coefficient. For winds between 20 and 48 meters per second, this coefficient initially increases and peaks at winds of about 32 meters per second before decreasing.
Comment on "Why Are There So Many Species of Herbivorous Insects in Tropical Rainforests?"
Authors: Norton David A. , Didham Raphael K.
Published: March 2007

Novotny
et al
. (Reports, 25 August 2006, p. 1115) argued that higher herbivore diversity in tropical forests results from greater phylogenetic diversity of host plants, not from higher host specificity. However, if host specificity is related to host abundance, differences in relative host abundance between tropical and temperate regions may limit any general conclusion that herbivore diversity scales directly with host-plant diversity.
Tunability and Noise Dependence in Differentiation Dynamics
Authors: Süel Gürol M. , Kulkarni Rajan P. , Dworkin Jonathan , Garcia-Ojalvo Jordi , Elowitz Michael B.
Published: March 2007

The dynamic process of differentiation depends on the architecture, quantitative parameters, and noise of underlying genetic circuits. However, it remains unclear how these elements combine to control cellular behavior. We analyzed the probabilistic and transient differentiation of
Bacillus subtilis
cells into the state of competence. A few key parameters independently tuned the frequency of initiation and the duration of competence episodes and allowed the circuit to access different dynamic regimes, including oscillation. Altering circuit architecture showed that the duration of competence events can be made more precise. We used an experimental method to reduce global cellular noise and showed that noise levels are correlated with frequency of differentiation events. Together, the data reveal a noise-dependent circuit that is remarkably resilient and tunable in terms of its dynamic behavior.
An Atomic Seesaw Switch Formed by Tilted Asymmetric Sn-Ge Dimers on a Ge (001) Surface
Authors: Tomatsu K. , Nakatsuji K. , Iimori T. , Takagi Y. , Kusuhara H. , Ishii A. , Komori F.
Published: March 2007

When tin (Sn) atoms are deposited on a clean germanium (Ge) (001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge-dimer position. We identified the dimer as a heterogeneous Sn-Ge dimer by reversing its buckling orientation with a scanning tunneling microscope (STM) at 80 kelvin. An atomic seesaw switch was formed for one-dimensional electronic conduction in the Ge dimer–row direction by using the STM to reversibly flip the buckling orientation of the Sn-Ge dimer and to set up standing-wave states.
Plumb Crazy
Authors: Renner Rebecca
Published: March 2007

The Great Lead Water Pipe Disaster
.
By Werner Troesken
. MIT Press, Cambridge, MA, 2006. 328 pp. $29.95, £19.95. ISBN 9780262201674.

Troesken explores the deleterious effects lead water pipes had on health and why evidence of such effects was ignored by public officials.
Dealing with Differences
Authors: Henderson A. Scott
Published: March 2007

The Measure of Merit
. Talents, Intelligence, and Inequality in the French and American Republics, 1750-1940.
By John Carson
. Princeton University Press, Princeton, NJ, 2007. 421 pp. $39.50, £26.95. ISBN 9780691017150.

Carson explores how two modern democracies have wrestled with the clash between their commitments to equality and scientific claims about disparities in human intelligence and talent.
Molecular Epidemiology ofMycobacterium abscessus, with Focus on Cystic Fibrosis
Authors: Jönsson Bodil E. , Gilljam Marita , Lindblad Anders , Ridell Malin , Wold Agnes E. , Welinder-Olsson Christina
Published: March 2007

Mycobacterium abscessushas been isolated increasingly often from the respiratory tracts of cystic fibrosis (CF) patients. It is not known whether these organisms are transmitted from person to person or acquired from environmental sources. Here, colony morphology and pulsed-field gel electrophoresis (PFGE) pattern were examined for 71 isolates ofM. abscessusderived from 14 CF patients, three non-CF patients with chronic respiratoryM. abscessusinfection or colonization, one patient with mastoiditis, and four patients with infected wounds, as well as for six isolates identified as environmental contaminants in various clinical specimens. Contaminants and wound isolates mainly exhibited smooth colony morphology, while a rough colony phenotype was significantly associated with chronic airway colonization (P= 0.014). Rough strains may exhibit increased airway-colonizing capacity, the cause of which remains to be determined. Examination by PFGE of consecutive isolates from the same patient showed that they all represented a single strain, even in cases where both smooth and rough isolates were present. When PFGE patterns were compared, it was shown that 24 patients had unique strains, while four patients harbored strains indistinguishable by PFGE. Two of these were siblings with CF. The other two patients, one of whom had CF, had not had contact with each other or with the siblings. Our results show that most patients colonized byM. abscessusin the airways have unique strains, indicating that these strains derive from the environment and that patient-to-patient transmission rarely occurs.
Synergistic Roles of Antibody and Interferon in Noncytolytic Clearance of Sindbis Virus from Different Regions of the Central Nervous System
Authors: Burdeinick-Kerr Rebeca , Wind Jennifer , Griffin Diane E.
Published: March 2007

Sindbis virus (SINV) is an alphavirus that causes infection of neurons and encephalomyelitis in adult immunocompetent mice. Recovery can occur without apparent neurological damage. To better define the factors facilitating noncytolytic clearance of SINV in different regions of the central nervous system (CNS) and the roles of innate and adaptive immune responses at different times during infection, we have characterized SINV infection and clearance in the brain, brain stem, and spinal cords of severe combined immunodeficiency (SCID) and C57BL/6 (wild-type [WT]) mice and mice deficient in beta interferon (IFN-β) (BKO), antibody (μMT), IFN-γ (GKO), IFN-γ receptor (GRKO), and both antibody and IFN-γ (μMT/GKO). WT mice cleared infectious virus by day 8, while SCID mice had persistent virus replication at all sites. For 3 days after infection, BKO mice had higher titers at all sites than WT mice, despite similar IFN-α production, but cleared virus similarly. GKO and GRKO mice cleared infectious virus from all sites by days 8 to 10 and, like WT mice, displayed transient reactivation at 12 to 22 days. μMT mice did not clear virus from the brain, and clearance from the brain stem and lumbar spinal cord was delayed, followed by reactivation. Eighty-one days after infection, μMT/GKO mice had not cleared virus from any site, but titers were lower than for SCID mice. These studies show that IFN-β is independently important for early control of CNS virus replication, that antiviral antibody is critical for clearance from the brain, and that both antibody and IFN-γ contribute to prevention of reactivation after initial clearance.
Nuclear and Nucleolar Targeting of Influenza A Virus NS1 Protein: Striking Differences between Different Virus Subtypes
Authors: Melén Krister , Kinnunen Leena , Fagerlund Riku , Ikonen Niina , Twu Karen Y. , Krug Robert M. , Julkunen Ilkka
Published: March 2007

Influenza A virus nonstructural protein 1 (NS1A protein) is a virulence factor which is targeted into the nucleus. It is a multifunctional protein that inhibits host cell pre-mRNA processing and counteracts host cell antiviral responses. We show that the NS1A protein can interact with all six human importin α isoforms, indicating that the nuclear translocation of NS1A protein is mediated by the classical importin α/β pathway. The NS1A protein of the H1N1 (WSN/33) virus has only one N-terminal arginine- or lysine-rich nuclear localization signal (NLS1), whereas the NS1A protein of the H3N2 subtype (Udorn/72) virus also has a second C-terminal NLS (NLS2). NLS1 is mapped to residues 35 to 41, which also function in the double-stranded RNA-binding activity of the NS1A protein. NLS2 was created by a 7-amino-acid C-terminal extension (residues 231 to 237) that became prevalent among human influenza A virus types isolated between the years 1950 to 1987. NLS2 includes basic amino acids at positions 219, 220, 224, 229, 231, and 232. Surprisingly, NLS2 also forms a functional nucleolar localization signal NoLS, a function that was retained in H3N2 type virus NS1A proteins even without the C-terminal extension. It is likely that the evolutionarily well-conserved nucleolar targeting function of NS1A protein plays a role in the pathogenesis of influenza A virus.
Poly(I:C) and Lipopolysaccharide Innate Sensing Functions of Circulating Human Myeloid Dendritic Cells Are Affected In Vivo in Hepatitis C Virus-Infected Patients
Authors: Rodrigue-Gervais Ian Gaël , Jouan Loubna , Beaulé Geneviève , Sauvé Dominike , Bruneau Julie , Willems Bernard , Sékaly Rafick-Pierre , Lamarre Daniel
Published: March 2007

The role of peripheral dendritic cells (DCs) in hepatitis C virus (HCV) infection is unclear. To determine if persistent infection exerts an inhibitory pressure on HCV-specific innate responses, we analyzed DC function in blood through quantification of cell-associated HCV RNA levels in conjunction with multiparametric flow cytometry analysis of pathogen recognition receptor-induced cytokine expression. Independently of the serum viral load, fluorescence-activated cell sorter-purified total DCs had a wide range of cell-associated HCV genomic RNA copy numbers (mean log
10
, 5.0 per 10
6
cells; range, 4.3 to 5.8). Here we report that for viremic patients with high viral loads in their total DCs, the myeloid DC (MDC) subset displayed impaired expression of interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-α) but normal IL-6 or chemokine CCL3 expression in response to poly(I:C) and lipopolysaccharide (LPS). IL-6-expressing cells from this subgroup of viremic patients demonstrated a significant increase (sixfold more) in TNF-α
−
IL-12
−
cell frequency compared to healthy donors (mean, 38.8% versus 6.5%;
P
< 0.0001), indicating a functional defect in a subpopulation of cytokine-producing MDCs (∼6% of MDCs). Attenuation of poly(I:C) and LPS innate sensing was HCV RNA density dependent and did not correlate with viremia or deficits in circulating MDC frequencies in HCV-infected patients. Monocytes from these patients were functionally intact, responding normally on a per-cell basis following stimulation, independent of cell-associated HCV RNA levels. Taken together, these data indicate that detection of HCV genomic RNA in DCs and loss of function in the danger signal responsiveness of a small proportion of DCs in vivo are interrelated rather than independent phenomena.
Human T-Cell Leukemia Virus Type 1 Tax Enhances Serum Response Factor DNA Binding and Alters Site Selection
Authors: Winter Heather Y. , Marriott Susan J.
Published: March 2007

Human T-cell leukemia virus type I (HTLV-1) is the etiological agent of adult T-cell leukemia. The viral transforming protein Tax regulates the transcription of viral and cellular genes by interacting with cellular transcription factors and coactivators. The effects of Tax on cellular gene expression have an important impact on HTLV-1-mediated cellular transformation. Expression of the c-
fos
cellular oncogene is regulated by serum response factor (SRF), and Tax is known to induce c-
fos
gene expression by activating SRF-responsive transcription. SRF activates cellular gene expression by binding to a consensus DNA sequence (CArG box) located within a serum response element (SRE). Since SRF activates transcription of many growth regulatory genes, this pathway is likely to have a significant impact on Tax-mediated transformation. Here we demonstrate that Tax interacts with SRF and enhances the binding of SRF to SREs located in the c-
fos
, Nur77, and viral promoters. Also, we establish that in the presence of Tax, SRF selects more divergent CArG box sequences than in the absence of Tax, revealing a novel mechanism for regulating SRF-responsive gene expression. Finally, increased association of SRF with chromatin and specific promoters was observed in Tax-expressing cells, correlating with increased c-
fos
and Nur77 mRNA levels in Tax-expressing cells. These results suggest that Tax activates SRF-responsive transcription by enhancing its binding affinity to multiple different SRE sequences.
A Combination of Naturally Occurring Mutations in North American West Nile Virus Nonstructural Protein Genes and in the 3′ Untranslated Region Alters Virus Phenotype
Authors: Davis C. Todd , Galbraith Sareen E. , Zhang Shuliu , Whiteman Melissa C. , Li Li , Kinney Richard M. , Barrett Alan D. T.
Published: March 2007

We previously reported mutations in North American West Nile viruses (WNVs) with a small-plaque (
sp
), temperature-sensitive (
ts
), and/or mouse-attenuated (
att
) phenotype. Using an infectious clone, site-directed mutations and 3′ untranslated region (3′UTR) exchanges were introduced into the WNV NY99 genome. Characterization of mutants demonstrated that a combination of mutations involving the NS4B protein (E249G) together with either a mutation in the NS5 protein (A804V) or three mutations in the 3′UTR (A10596G, C10774U, A10799G) produced
sp
,
ts
, and/or
att
variants. These results suggested that the discovery of North American WNV-phenotypic variants is rare because of the apparent requirement of concurrent polygenic mutations.
Conformation-Specific Antibodies Targeting the Trimer-of-Hairpins Motif of the Human T-Cell Leukemia Virus Type 1 Transmembrane Glycoprotein Recognize the Viral Envelope but Fail To Neutralize Viral Entry
Authors: Mirsaliotis Antonis , Nurkiyanova Kulpash , Lamb Daniel , Woof Jenny M. , Brighty David W.
Published: March 2007

Human T-cell leukemia virus type 1 (HTLV-1) entry into cells is dependent upon the viral envelope glycoprotein-catalyzed fusion of the viral and cellular membranes. Following receptor activation of the envelope, the transmembrane glycoprotein (TM) is thought to undergo a series of fusogenic conformational transitions through a rod-like prehairpin intermediate to a compact trimer-of-hairpins structure. Importantly, synthetic peptides that interfere with the conformational changes of TM are potent inhibitors of membrane fusion and HTLV-1 entry, suggesting that TM is a valid target for antiviral therapy. To assess the utility of TM as a vaccine target and to explore further the function of TM in HTLV-1 pathogenesis, we have begun to examine the immunological properties of TM. Here we demonstrate that a recombinant trimer-of-hairpins form of the TM ectodomain is strongly immunogenic. Monoclonal antibodies raised against the TM immunogen specifically bind to trimeric forms of TM, including structures thought to be important for membrane fusion. Importantly, these antibodies recognize the envelope on virally infected cells but, surprisingly, fail to neutralize envelope-mediated membrane fusion or infection by pseudotyped viral particles. Our data imply that, even in the absence of overt membrane fusion, there are multiple forms of TM on virally infected cells and that some of these display fusion-associated structures. Finally, we demonstrate that many of the antibodies possess the ability to recruit complement to TM, suggesting that envelope-derived immunogens capable of eliciting a combination of neutralizing and complement-fixing antibodies would be of value as subunit vaccines for intervention in HTLV infections.
Epstein-Barr Virus Inhibits Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication in Primary Effusion Lymphomas
Authors: Xu Dongsheng , Coleman Tricia , Zhang Jun , Fagot Ashley , Kotalik Catherine , Zhao Lingjun , Trivedi Pankaj , Jones Clinton , Zhang Luwen
Published: March 2007

The majority of AIDS-associated primary effusion lymphomas (PEL) are latently infected with both Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV). PELs harboring two viruses have higher oncogenic potential, suggesting functional interactions between EBV and KSHV. The KSHV replication and transcription activator (K-RTA) is necessary and sufficient for induction of KSHV lytic replication. EBV latent membrane protein 1 (LMP-1) is essential for EBV transformation and establishment of latency in vitro. We show EBV inhibits chemically induced KSHV lytic replication, in part because of a regulatory loop in which K-RTA induces EBV LMP-1 and LMP-1 in turn inhibits K-RTA expression and furthermore the lytic gene expression of KSHV. Suppression of LMP-1 expression in dually infected PEL cells enhances the expression of K-RTA and lytic replication of KSHV upon chemical induction. Because LMP-1 is known to inhibit EBV lytic replication, KSHV-mediated induction of LMP-1 would potentiate EBV latency. Moreover, KSHV infection of EBV latency cells induces LMP-1, and K-RTA is involved in the induction. Both LMP-1 and K-RTA are expressed during primary infection by EBV of KSHV latency cells. Our findings provide evidence that an interaction between EBV and KSHV at molecular levels promotes the maintenance and possibly establishment of viral latency, which may contribute to pathogenesis of PELs.
Nature and origin of sediments infilling poorly defined buried bedrock valleys adjacent to the Niagara Escarpment, southern Ontario, Canada
Authors: Meyer Patricia A , Eyles Carolyn H
Published: March 2007

The buried Paleozoic bedrock surface of southern Ontario is dissected by an interconnected system of valleys. These buried valleys are infilled with thick successions of glacial, interglacial, and fluvial sediments that contain a lengthy record of changing environmental conditions during the late Quaternary. Detailed logging of over 500 m of sediment recovered from 11 continuously cored boreholes provides the basis for this study. The boreholes were drilled within two poorly defined bedrock valleys located east of the Niagara Escarpment in southern Ontario as part of a groundwater exploration program. Six distinct facies types were identified within the cores: sand, gravel, fine-grained sediment, and sand-rich, mud-rich, and clast-rich diamict. Textural characteristics of the cored sediments and vertical changes in facies types were used to identify six stratigraphic units (SU I through SU VI) within the valley-infill deposits. These units are interpreted to record fluvial or colluvial (SU I), lacustrine (SU II), fluvial, glaciofluvial or deltaic (SU III), subglacial (SU IV), glaciofluvial (SU V) and subglacial or ice marginal (SU VI) conditions. Sediment characteristics and stratigraphic relationships allow tentative correlation with known surficial deposits. Analysis of the subsurface characteristics and geometries of this stacked succession of coarse- and fine-grained stratigraphic units also allows identification of the geometry of potential aquifers.
Origin, age, and paleoenvironmental significance of carbonate precipitates from a granitic environment, Akshayuk Pass, southern Baffin Island, Canada
Authors: Lacelle Denis , Lauriol Bernard , Clark Ian D
Published: March 2007

This study documents the discovery of calcite crusts on the upper surface of clasts within morainic complexes in Akshayuk Pass, southern Cumberland Peninsula (Baffin Island), a region underlain by granitic and gneissic rocks of the Precambrian Canadian Shield. Strontium isotope ratios (87Sr/86Sr) indicate that the major source of calcium is derived from the local dissolution of fracture-filling calcite and a minor source is derived from silicate weathering. The calcite crusts have δ13C values between 1.6 and 12.0 and δ18O values in the –13.0 and –7.9 range. These values are highly enriched over the predicted isotopic values based on the δ13CDIC and δ18O of the local water and temperature at which calcite precipitation occurred. The isotopic enrichments are attributed to a combination of both equilibrium and kinetic evaporation and were verified experimentally. The series of evaporative experiments indicate that kinetic evaporation produces a far-from-equilibrium isotope effect on both the δ13C and δ18O composition of the precipitating calcite (13CKIE CaCO3–CO2 between 20.2 and 40.5 VPDB; 18OKIE averaging 34.9% ± 3.7% VSMOW). Based on these results, the formation of the calcite crusts is ascribed to the evaporation of stagnating ephemeral lakes and streams following the retreat of valley glaciers. Given the >1500 m difference in heights between the highland and the valley, the katabatic winds originating from the Penny Ice Cap can act as a catalyst to increase the rate of evaporation. In addition, radiocarbon dating of ten of these crusts yielded Holocene ages (7640 cal (calibrated) BP to modern). These results suggest that the maximum expansion of Holocene valley glacier in Akshayuk Pass, previously thought to have occurred during the Little Ice Age, is probably much older.
Tracking seasonal migrations of redfish (Sebastes spp.) in and around the Gulf of St. Lawrence using otolith elemental fingerprints
Authors: Campana Steven E , Valentin Alexandra , Sévigny Jean-Marie , Power Don
Published: March 2007

Large concentrations of beaked redfish (Sebastes mentella and Sebastes fasciatus) overwinter in the Cabot Strait and the approaches of the Gulf of St. Lawrence each year. Synoptic research vessel surveys indicate that redfish are distributed more widely in the summer than in the winter, particularly within the Gulf. Significant differences in the trace element composition of the otolith ("otolith elemental fingerprint") were observed among summer aggregations, indicating that the aggregations maintained some degree of separation while in the Gulf. Sebastes mentella and S. fasciatus were readily distinguished based on otolith elemental fingerprints. Using the elemental fingerprints of the summer samples as a natural tag, we found that S. mentella tended to move out of the Gulf in the winter. Aggregations of S. mentella found in the east during the summer were not found in our winter collections. The elemental fingerprints of S. mentella from the Saguenay Fjord were clearly distinct from redfish further east in the Gulf of St. Lawrence, indicating that this group had been separated from other redfish for much of their life. The implications of our findings extend not only to the fisheries management of redfish, but also to the extent of movement expected of deepwater fish species.
Environmental implications of stratification and turbulent mixing in a shallow lake basin
Authors: Loewen Mark R , Ackerman Josef Daniel , Hamblin Paul F
Published: March 2007

The extent of stratification and vertical mixing in the water column (7–11 m deep) was investigated over an offshore reef in the western basin of Lake Erie. Measurements reveal that the vertical transport of oxygen and heat is controlled by the complex interaction of several physical mechanisms. Generally, when the wind speed (W) was >7 m·s–1 and the air was cooler than the water (Tair< Tw), the water column was well mixed due to turbulent mixing. However, when W < 7 m·s–1 (~65% of the summer), turbulence was too weak to overcome the stratification and mix the water column. An analysis of 25 years of meteorological data revealed that a period of 4.5 ± 1.9 days of calm, warm weather (W < 7 m·s–1 and Tair > Tw) occurs every year. Results indicate that there is strong probability of hypoxia due to stratification (i.e., when diffusivities < 10–6 m2·s–1) and sediment oxygen demand (i.e., 0.1–1.0 g·m–2·day–1) during these periods. The environmental implications of stratification to water quality and its effects on benthic organisms, such as the burrowing mayfly (Hexagenia spp.), require further considerations in large temperate lakes and basins that are sufficiently shallow that there is no permanent seasonal stratification.
Changes in baseline growth and maturation parameters of Northwest Atlantic porbeagle, Lamna nasus, following heavy exploitation
Authors: Cassoff Rachel M , Campana Steven E , Myklevoll Sigmund
Published: March 2007

We tested for density-dependent changes in growth and maturation of Northwest Atlantic porbeagle (Lamna nasus) after the population declined by 75%–80% from fishing. Vertebrae and reproductive data collected from the virgin (1961–1966) and exploited (1993–2004) populations were analysed to test for differences in growth rate and age and length at maturity between the time periods. We detected significant differences between reparameterized von Bertalanffy growth models for each period, using likelihood ratio tests. Beyond an age of 7 years, mean length at age was greater during 1993–2004 than during 1961–1966. Between 1961–1963 and 1999–2001, length at maturity decreased in males (from 179 to 174 cm curved fork length (CFL)) and was invariant in females (216 cm CFL), whereas age at maturity declined in both males (from 8 to 7 years) and females (from 19 to 14 years). An analysis of porbeagle temperature associations indicated that sharks occupied comparable temperature conditions during the mid-1960s and 1990s, ruling out the possibility of temperature-induced growth changes. The observed increase in growth rate and decrease in age at maturity following exploitation support the hypothesis of a compensatory density-dependent growth response.
The role of seasonally altering photoperiod in regulating physiology in Atlantic cod (Gadus morhua). Part I. Sexual maturation
Authors: Davie Andrew , Porter Mark JR , Bromage Niall R , Migaud Herve
Published: March 2007

While the Atlantic cod (Gadus morhua) displays clear seasonality in its reproductive cycle, the exact photic signal that entrains this rhythm is yet undefined. This present work developed a model to describe the photic regulation of reproduction in the species in comparison with other commercially important temperate teleosts. This was achieved through the strategic masking of the natural photoperiod cycle during the first 2 years of life with the application of continuous illumination. The results demonstrated that it is the falling autumnal photoperiod signal after the summer solstice, more specifically after October, that is responsible for recruiting individuals to enter the sexual maturation cycle. Furthermore, in all treatments where this signal was masked through the application of continuous illumination, there was no significant reproductive activity and growth was improved by up to 60% at 27 months posthatch. This information is of particular value to the developing cod aquaculture industry in which the management of reproduction using artificial photoperiod manipulation will be of vital economic importance.
The role of seasonally altering photoperiod in regulating physiology in Atlantic cod (Gadus morhua). Part II. Somatic growth
Authors: Davie Andrew , Porter Mark JR , Bromage Niall R , Migaud Herve
Published: March 2007

Research to date has not clearly defined the role of photoperiod in regulating somatic growth in Atlantic cod (Gadus morhua). The present study followed individual growth performance, plasma insulin-like growth factor-I, and relative liver size in response to a range of experimental photoperiod treatments where populations were transferred from an ambient photoperiod regime to continuous illumination at strategic times during the first 2 years of life. While this work demonstrated that application of continuous illumination could directly stimulate somatic growth, this growth stimulation is transitory with no accumulative effect of prolonged exposure to continuous illumination. Importantly, it was apparent that the photic inhibition of maturation realized a far more significant growth stimulation, and in populations where this occurred, sexually dimorphic growth patterns became apparent. Plasma insulin-like growth factor-I displays a seasonal rhythm correlated with ambient temperature under natural photic conditions and in certain circumstances could be used as an accurate predictor of growth rate. Overall, this work further refines the guidelines on photoperiod management during commercial ongrowing of the species to help realize the maximum economic potential of cod aquaculture.
Nonrandom mating in a broadcast spawner: mate size influences reproductive success in Atlantic cod (Gadus morhua)
Authors: Rowe Sherrylynn , Hutchings Jeffrey A , Skjæraasen Jon Egil
Published: March 2007

We tested the hypothesis that reproductive success in Atlantic cod (Gadus morhua) is random with respect to similarity in body size between mates. Immediately prior to their natural breeding periods, groups of 52–93 cod from three Northwest Atlantic populations were transported to a large (15 m diameter, 4 m deep) tank where they spawned undisturbed at densities similar to those in nature. Based on microsatellite DNA-parentage assignment of 8913 offspring from four spawning groups, females and males achieved their highest reproductive success when breeding with mates that were larger than themselves. Our observations are consistent with the hypothesis that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that this can have an important influence on individual fitness. Our results further suggest that reductions in the mean and variance in body size of commercially exploited marine fishes concomitant with size-selective harvesting may have greater negative consequences for population recovery than previously thought.
Interaction between temperature and photoperiod on growth and feeding of Atlantic cod (Gadus morhua): possible secondary effects
Authors: Imsland Albert Kjartansson , Foss Atle , Alvseike Thomas , Folkvord Arild , Stefansson Sigurd Olav , Jonassen Thor Magne
Published: March 2007

Interactions between temperature and photoperiod on growth of Atlantic cod (Gadus morhua) juveniles (initial weight 9.1 g) were studied by rearing juvenile cod 3 months under simulated natural photoperiod (LDN) and continuous light (LD24:0) at 7, 10, and 13 °C. Juvenile Atlantic cod exposed to LD24:0 had higher growth rate and better feed conversion efficiency compared with cod reared under LDN. Optimal temperature for growth of juvenile Atlantic cod in the size range 5–50 g was influenced by photoperiod and was estimated to be 12.3 °C under LD24:0 and 15.7 °C under LDN. After termination of the laboratory study, the fish were reared in sea pens at ambient conditions for 17 months. The growth-enhancing effect of LD24:0 could be traced far beyond the duration of the laboratory trial, as the final mean weights in June 2005 of the fish reared at LD24:0 and 13 and 10 °C in the laboratory trial were 8% and 13% higher than those of the respective LDN groups. Our study indicates a physiological mechanism that might be linked to cod migrations, as maximal growth and feeding efficiency will be attained in areas during a season with extended day length or continuous light.
Multifrequency backscattering properties of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii)
Authors: Fässler Sascha M.M. , Santos Rita , García-Núñez Norma , Fernandes Paul G
Published: March 2007

The multifrequency backscattering characteristics of echotraces of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii) are described. These fish cohabit similar areas of the North Sea in summer and echotraces of their schools are difficult to distinguish. Mean volume backscattering strengths at 18, 38, 120, and 200 kHz were taken from the International North Sea Herring Acoustic Surveys along with coincident pelagic trawl samples. The results indicate that echotraces of these fish species cannot be distinguished on the basis of differences in backscattering at discrete frequencies typically used in fish surveys and on fishing vessels. However, some discrimination between herring size-classes was evident. The empirical data for herring were then compared with a backscattering model for herring combining fish flesh, the swimbladder, and the effect of increased pressure at depth. Both the empirical data and model data indicate that, compared with large herring, progressively smaller herring generally have higher backscattering at the lowest frequency (18 kHz), although variability was high. According to the model, this frequency-specific signature is due to the progressively more significant contribution made by the fish body compared with the swimbladder, as the latter diminishes owing to an increase in ambient pressure in deeper water.
Three-dimensional photogrammetry as a tool for estimating morphometrics and body mass of Steller sea lions (Eumetopias jubatus)
Authors: Waite Jason N , Schrader Wendy J , Mellish Jo-Ann E , Horning Markus
Published: March 2007

A technique was developed to estimate morphometrics and body mass of Steller sea lions (Eumetopias jubatus) using three-dimensional (3D) photogrammetry. 3D photogrammetry reduces many of the problems associated with camera and body position encountered with two-dimensional photogrammetric techniques, allowing body mass estimation of free-ranging, active sea lions, without sedation, heavy weighing equipment, and disturbance. 3D computer wireframes of 53 Steller sea lions of various age classes were generated from multiple time-synchronous digital photos and used to estimate length, girth, and volume. Average estimates of standard length and axillary girth were within ±2.5% and ±4.0% of physically measured dimensions, respectively. Average estimates of standard length and axillary girth using only wireframes based on ideal body postures were within ±1.7% and ±3.1% of physically measured dimensions, respectively. Regressions of physically measured mass on photogrammetrically estimated body volume yielded a predictive model. Body mass estimates using this model were on average within 9.0% (95% confidence interval = ±1.7%) of the physically measured mass. This technique was also successfully applied to reptiles and fish.
General variable separation solution and new localized excitations for the (2 + 1)-dimensional nonlinear Schrödinger equation
Authors: Bai Cheng -Lin , Hu Hai -Quan , Wang Wen -Jun , Zhao Hong
Published: March 2007

By applying a special Bäcklund transformation, a general variable separation solution for the (2 + 1)-dimensional nonlinear Schrödinger equation is derived. In addition to some types of the usual localized excitations, such as dromions, lumps, ring solitons, oscillated dromions, and breathers, soliton structures can be easily constructed by selecting arbitrary functions appropriately. A new class of localized excitations, like fractal-dromions, fractal-lumps, peakons, compactons, and folded excitations of this system is found by selecting appropriate functions. Some interesting novel features of these structures are revealed.PACS Nos.: 05.45.–a, 02.30.Jr
The Pioneer anomaly: seeking an explanation in newly recovered data
Authors: Toth Viktor T , Turyshev Slava G
Published: March 2007

The Pioneer 10 and 11 spacecraft yielded very accurate navigation in deep space that was, however, limited by a small, anomalous frequency drift of their carrier signals received by the radio-tracking stations of the NASA Deep Space Network (DSN). This drift signifies a discrepancy between the frequency of the Doppler signals observed by the DSN and that frequency modeled using modern-day deep space navigational codes. This discrepancy, evident in the data for both spacecraft, was interpreted as an approximately constant acceleration. This acceleration has become known as the Pioneer anomaly. The origin of this anomaly is yet unknown. Recent efforts to explain the effect included a search for independent confirmation, analyses of conventional mechanisms, even ideas rooted in new physics, and proposals for a dedicated mission. We assert that to determine the origin of the Pioneer anomaly, and especially before any discussion of new physics and (or) a dedicated mission can take place, one must analyze the entire set of radiometric Doppler data received from Pioneer 10 and 11. In this paper, we report on our efforts to recover and utilize the complete set of radio Doppler and telemetry records of the Pioneer 10 and 11 spacecraft. The collection of radio Doppler data for both missions is now complete; we are ready to begin its evaluation. We also make progress utilizing the recently recovered Pioneer telemetry data in the development of a complete engineering profile of the spacecraft. We present a strategy for studying the effect of on-board-generated small forces with this newly recovered information on the performance of thermal, electrical, power, communication, and other subsystems, in conjunction with the analysis of the entire set of the Pioneer Doppler data. We report on the preparations for the upcoming analysis of the newly recovered data with the ultimate goal of determining the origin of the Pioneer anomaly. Finally, we discuss implications of our on-going research of the Pioneer anomaly for other missions, most notably for New Horizons, NASA's recently launched mission to Pluto. PACS Nos.: 95.10.Ce, 95.10.Eg, 95.30.Sf, 95.55.Pe
Reduced surface integral equations for Laplacian fields in the presence of layered bodies
Authors: Ciric I R
Published: March 2007

Laplacian potential fields in stratified media are usually analyzed using an integral equation for an unknown function over the union of all the interfaces between regions with different homogeneous materials. In this paper, the field problem is solved using a reduced integral equation involving a single unknown function over only the boundary of the source region. The new integral equation is derived by introducing surface operators to express the potential and its normal derivative on each interface in terms of a single unknown function over the same interface. These operators and the corresponding single functions are obtained recursively, from one interface to the next. Thus, a substantial decrease in the amount of necessary numerical computation and computer memory is achieved especially for systems containing identical layered bodies where the reduction operators are only constructed for one of the bodies. The purpose of this paper is to derive reduced integral equations by directly applying the interface conditions and to show their high computational efficiency for systems of layered bodies.PACS Nos.: 02.30.Rz, 02.70.Pt, 41.20.Cv
A heat transfer model of crown scorch in forest fires
Authors: Michaletz S T , Johnson E A
Published: March 2007

The Van Wagner crown scorch model is widely used to estimate crown component necroses in surface fires. The model is based on buoyant plume theory but accounts for crown heat transfer processes using an empirical proportionality factor k. Crown scorch estimates have used k values for foliage, but k varies with heat transfer characteristics, and branch and bud necroses are more relevant to tree mortality. This paper derives and validates a more physically complete model of crown scorch in surface fires (I ≤ 2500 kW·m–1). The model links a buoyant plume model with a lumped capacitance heat transfer analysis applicable to branches, buds, and foliage (~1 cm maximum diameter). The lumped capacitance analysis is validated with vegetative-bud heating experiments, and the entire heat transfer model of crown scorch is validated with fireline intensity and foliage necrosis data. The model is more general than the Van Wagner model and is independent of experimental fire data. Predictions require measurements of fireline intensity, residence time, ambient temperature, and five thermophysical properties of crown components. The model predicts differences between bud and foliage necrosis heights, and illustrates why heat transfer processes should be considered in crown scorch models.
Rating the susceptibility of forests to mountain pine beetle infestations: the impact of data
Authors: Nelson T , Boots B , Wulder M A , Shore T , Safranyik L , Ebata T
Published: March 2007

British Columbia is currently experiencing the largest mountain pine beetle (Dendroctonus ponderosae Hopkins) epidemic on record. The spatial extent of this infestation highlights the need for large-area forest management. We explore the use of three large-area data sets for implementing a stand-scale model of forest susceptibility that quantifies the probability of loss of pine basal area because of attack by the mountain pine beetle. Using these data sets, we investigate the impact of surrogate variables, which is necessary when variables required for the susceptibility model are not present in a data set. The impact of the source data information content on the susceptibility model output is also analyzed. Results indicate that the susceptibility model is sensitive to both surrogate variables and data sources and suggest that landscape level application of the susceptibility model, which was developed using stand-scale relationships, is problematic. Of particular concern is the use of photointerpreted data sets for model parameterization. The information content in photointerpreted data sets is much different than data on similar forest characteristics collected in the field and provides an inadequate substitute for implementing the forest susceptibility model.
Evaluating a model for predicting active crown fire rate of spread using wildfire observations
Authors: Alexander Martin E , Cruz Miguel G
Published: March 2007

We evaluated the predictive capacity of a rate of spread model for active crown fires (M.G. Cruz, M.E. Alexander, and R.H. Wakimoto. 2005. Can. J. For. Res. 35: 1626–1639) using a relatively large (n = 57) independent data set originating from wildfire observations undertaken in Canada and the United States. The assembled wildfire data were characterized by more severe burning conditions and fire behavior in terms of rate of spread and the degree of crowning activity than the data set used to parameterize the crown fire rate of spread model. The statistics used to evaluate model adequacy showed good fit and a level of uncertainty considered acceptable for a wide variety of fire management and fire research applications. The crown fire rate of spread model predicted 42% of the data with an error lower then ±25%. Mean absolute percent errors of 51% and 60% were obtained for Canadian and American wildfires, respectively. The characteristics of the data set did not allow us to determine where model performance was weaker and consequently identify its shortcomings and areas of future improvement. The level of uncertainty observed suggests that the model can be readily utilized in support of operational fire management decision making and for simulations in fire research studies.