bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple and Interconnected Pathways for
l
-Lysine Catabolism in
Pseudomonas putida
KT2440
Authors: Revelles Olga , Espinosa-Urgel Manuel , Fuhrer Tobias , Sauer Uwe , Ramos Juan L.
Published: October 2005

l
-Lysine catabolism in
Pseudomonas putida
KT2440 was generally thought to occur via the aminovalerate pathway. In this study we demonstrate the operation of the alternative aminoadipate pathway with the intermediates
d
-lysine,
l
-pipecolate, and aminoadipate. The simultaneous operation of both pathways for the use of
l
-lysine as the sole carbon and nitrogen source was confirmed genetically. Mutants with mutations in either pathway failed to use
l
-lysine as the sole carbon and nitrogen source, although they still used
l
-lysine as the nitrogen source, albeit at reduced growth rates. New genes were identified in both pathways, including the
davB
and
davA
genes that encode the enzymes involved in the oxidation of
l
-lysine to δ-aminovaleramide and the hydrolysis of the latter to δ-aminovalerate, respectively. The
amaA
,
dkpA
, and
amaB
genes, in contrast, encode proteins involved in the transformation of Δ
1
-piperidine-2-carboxylate into aminoadipate. Based on
l
-[U-
13
C, U-
15
N]lysine experiments, we quantified the relative use of pathways in the wild type and its isogenic mutants. The fate of
13
C label of
l
-lysine indicates that in addition to the existing connection between the
d
- and
l
-lysine pathways at the early steps of the catabolism of
l
-lysine mediated by a lysine racemase, there is yet another interconnection at the lower end of the pathways in which aminoadipate is channeled to yield glutarate. This study establishes an unequivocal relationship between gene and pathway enzymes in the metabolism of
l
-lysine, which is of crucial importance for the successful colonization of the rhizosphere of plants by this microorganism.
Characterization of Bacterial Drug Antiporters Homologous to Mammalian Neurotransmitter Transporters
Authors: Vardy Eyal , Steiner-Mordoch Sonia , Schuldiner Shimon
Published: October 2005

Multidrug transporters are ubiquitous proteins, and, based on amino acid sequence similarities, they have been classified into several families. Here we characterize a cluster of archaeal and bacterial proteins from the major facilitator superfamily (MFS). One member of this family, the vesicular monoamine transporter (VMAT) was previously shown to remove both neurotransmitters and toxic compounds from the cytoplasm, thereby conferring resistance to their effects. A BLAST search of the available microbial genomes against the VMAT sequence yielded sequences of novel putative multidrug transporters. The new sequences along with VMAT form a distinct cluster within the dendrogram of the MFS, drug-proton antiporters. A comparison with other proteins in the family suggests the existence of a potential ion pair in the membrane domain. Three of these genes, from
Mycobacterium smegmatis
,
Corynebacterium glutamicum
, and
Halobacterium salinarum
, were cloned and functionally expressed in
Escherichia coli
. The proteins conferred resistance to fluoroquinolones and chloramphenicol (at concentrations two to four times greater than that of the control). Measurement of antibiotic accumulation in cells revealed proton motive force-dependent transport of those compounds.
Tol-Dependent Macromolecule Import through theEscherichia coliCell Envelope Requires the Presence of an Exposed TolA Binding Motif
Authors: Pommier Stéphanie , Gavioli Marthe , Cascales Eric , Lloubès Roland
Published: October 2005

The Tol-Pal proteins of the cell envelope ofEscherichia coliare required for maintaining outer membrane integrity. This system forms protein complexes in which TolA plays a central role by providing a bridge between the inner and outer membranes via its interaction with the Pal lipoprotein. The Tol proteins are parasitized by filamentous bacteriophages and group A colicins. The N-terminal domain of the Ff phage g3p protein and the translocation domains of colicins interact directly with TolA during the processes of import through the cell envelope. Recently, a four-amino-acid sequence in Pal has been shown to be involved in Pal's interaction with TolA. A similar motif is also present in the sequence of two TolA partners, g3p and colicin A. Here, a mutational study was conducted to define the function of these motifs in the binding activity and import process of TolA. The various domains were produced and exported to the bacterial periplasm, and their cellular effects were analyzed. Cells producing the g3p domain were tolerant to colicins and filamentous phages and had destabilized outer membranes, while g3p deleted of three residues in the motif was affected in TolA binding and had no effect on cell integrity or colicin or phage import. A conserved Tyr residue in the colicin A translocation domain was involved in TolA binding and colicin A import. Furthermore, in vivo and in vitro coprecipitation analyses demonstrated that colicin A and g3p N-terminal domains compete for binding to TolA.
Replacement of Tyrosine 181 by Phenylalanine in Gentisate 1,2-Dioxygenase I from
Pseudomonas alcaligenes
NCIMB 9867 Enhances Catalytic Activities
Authors: Tan Chew Ling , Yeo Chew Chieng , Khoo Hoon Eng , Poh Chit Laa
Published: October 2005

xlnE
, encoding gentisate 1,2-dioxygenase (EC 1.13.11.4), from
Pseudomonas alcaligenes
(P25X) was mutagenized by site-directed mutagenesis. The mutant enzyme, Y181F, demonstrated 4-, 3-, 6-, and 16-fold increases in relative activity towards gentisate and 3-fluoro-, 4-methyl-, and 3-methylgentisate, respectively. The specific mutation conferred a 13-fold higher catalytic efficiency (
k
cat
/

K
m

) on Y181F towards 3-methylgentisate than that of the wild-type enzyme.
Truffle abundance in riparian and upland mixed-conifer forest of California's southern Sierra Nevada
Authors: Meyer Marc D , North Malcolm P
Published: October 2005

We compared the abundance, diversity, and composition of truffles in riparian and upland areas within a mixed-conifer forest of the Sierra Nevada of California. We sampled for truffles in a single watershed over two seasons (spring and summer) and 4 years to determine whether truffles were more abundant and diverse in riparian than upland sites in old-growth, mixed-conifer forest. Truffle frequency, biomass, and species richness were greater in riparian sites than in upland sites in both spring and summer samples. Species composition of truffles also was different between sites, with nine and one species found exclusively in riparian and upland sites, respectively. Distance between the center of truffle plots to logs and trees was lower and soil moisture was greater in riparian sites compared with upland sites, suggesting that log density, tree proximity, and soil moisture may influence truffle production in these habitats. Our study underscores the importance of riparian areas for truffles, a primary food source for northern flying squirrels (Glaucomys sabrinus) in the Sierra Nevada of California.Key words: truffles, riparian, Sierra Nevada.
Germination characteristics of Artemisia ordosica (Asteraceae) in relation to ecological restoration in northern China
Authors: Zheng Yuanrun , Rimmington Glyn M , Gao Yong , Jiang Lianhe , Xing Xuerong , An Ping , El-Sidding Kamal , Shimizu Hideyuki
Published: October 2005

Artemisia ordosica Krasch. (Asteraceae) is the dominant psammophytic shrub species on the Ordos Plateau of northern China and is used for revegetation of semi-arid areas. Experiments were conducted to determine the effects of light intensity, constant temperature, alternating temperatures, and water potential on germination to determine why air-dispersed achenes fail to germinate well in the field. Achenes germinated within a wide alternating temperature window, except under the 5:15 °C (night:day) temperature regime in darkness. Final percent germination (FPG) was higher in darkness than in light at alternating temperature regimes, except under the 20:30 °C (night:day) temperature regime. Achenes subjected to a range of constant temperatures in the dark had high FPG over 76.8% except at 30 °C (8%). Photosynthetic photon flux densities (PPFD) of 100 and 400 µmol·m2·s1 significantly lowered FPG under a 10:20 °C (night:day) regime, while at 025 µmol·m2·s1 PPFD, the FPG was over 92%. Few achenes germinated at 1.4 MPa. The most suitable temperature for germination of achenes placed under water stress was 20 °C. The best timing for air dispersal is mid-May, so seeds would become covered with sand at a time when temperature and soil moisture conditions were optimal for germination.Key words: air dispersal, Artemisia ordosica, hydrothermal time, psammophytes, semi-arid regions, temperature.
Lichens from the Hudson Bay Lowlands: northeastern coastal regions of Wapusk National Park in Manitoba
Authors: Piercey-Normore Michele D
Published: October 2005

Lichens are an important component of most terrestrial ecosystems including the subarctic tundra. A narrow band of raised calcareous beach ridges on the Hudson Bay Lowlands supports subarctic tundra alternating with incipient wetlands. This is the first extensive study of lichens on these beach ridges providing valuable noteworthy additions to the flora of Manitoba and baseline data for a developing national park. This study reports 134 species of lichens and seven habitats containing lichen communities; three of the lichens are new reports for Manitoba. Trends in the data were explored among 932 specimens (134 species) and three characters, method of reproduction, growth form, and substratum. The sexually reproducing crustose lichens were found mainly in exposed microenvironments such as on rocks and driftwood. The vegetatively reproducing fruticose lichens grew in the more stable microenvironments such as among moss on the ground. The sexually and vegetatively reproducing foliose lichens, occurring in a wide range of microenvironments and substrata, were more suited to the exposed beach ridge habitats than were either the crustose or fruticose lichens alone. Genetically and symbiotically diverse populations of both algal and fungal partners, resulting from sexual reproduction, would be better equipped than vegetative populations to adapt to changing environments in these exposed habitats.Key words: distribution, floristic survey, growth form, life history strategies, raised beach ridge, reproduction.
Seismicity in the vicinity of the SNORCLE corridors of the northern Canadian Cordillera
Authors: Cassidy John F , Rogers Garry C , Ristau J
Published: October 2005

The Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) corridors of the northern Cordillera sample some of the most, and least, seismically active regions of Canada. The earthquake history of this region is short. Precise determination of earthquake locations and depths is not possible even today. Nonetheless, significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earthquakes, microseismicity studies, and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes. This article summarizes our current knowledge of the seismicity and seismic hazards across the region. These detailed analyses have shown that (i) the largest historical earthquakes have occurred in regions of ongoing microseismicity; (ii) the largest earthquakes have occurred in pairs or in swarms, suggesting that stress triggering is important in this region; (iii) the active faults are concentrated in the offshore region; (iv) there is a concentration of seismicity in the Fold and Thrust belt, several hundred kilometres from the active plate margin; and (v) there is no seismicity associated with the Quaternary volcanic zone in northern British Columbia. Potentially damaging (magnitude M ≥ 5) earthquakes can be expected every few years in the vicinity of the northern Cordillera. The Mw = 7.9 Denali, Alaska, earthquake (where Mwis the moment magnitude) was a good reminder that the effects of a large earthquake can be substantial, even hundreds of kilometres from the epicentre. Detailed studies of seismicity, earth structure, and tectonics, with the latter made possible in large part by the SNORCLE transect, will allow for informed decision-making for resource development and the design of safe structures and infrastructure in the northern Canadian Cordillera.
The Archean deep-marine environment: turbidite architecture of the Burwash Formation, Slave Province, Northwest Territories
Authors: Ferguson Mark E , Waldron John WF , Bleeker Wouter
Published: October 2005

The Slave Province is an Archean craton that contains an unusually large proportion of preserved sedimentary rock, including thick turbidite successions. The Burwash Formation is exposed in the southern Slave Province between the Anton and Sleepy Dragon basement massifs. At the base of the succession, volcanics and clastic metasedimentary rocks of the Raquette Lake Formation record initiation of the basin in a rifted arc environment. These are overlain by thin black slates representing a transgression, followed by well over 5 km of Burwash Formation metamorphosed turbiditic sandstones and slates interspersed with thin felsic tuff layers. Lateral correlation within the formation is possible using airphotos and recognizable tuff units. Burwash Formation sandstones include thinly bedded units displaying Bouma sequences and thicker bedded units with scour-and-fill structures and stratification bands, characteristic of dense sediment gravity flows. The sedimentary rocks are organized in architectural elements that include channel-fill sandstones and conglomerates, muddy levees, interchannel sandstones resembling high-amplitude reflection packages (HARPs) described from modern fans, and possible depositional lobes. The overall sedimentary architecture was probably controlled by events in the tectonically active source area or areas. The Archean turbidites resemble their Phanerozoic and modern analogues, although they show less voluminous levees, and are generally less organized, than large modern passive-margin fans, which probably have no equivalents in the Archean.
MesozoicCenozoic paleomagnetism of the Intermontane and YukonTanana terranes, Canadian Cordillera
Authors: Symons D TA , Harris M J , McCausland P JA , Blackburn W H , Hart C JR
Published: October 2005

Lithoprobe Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) transect support enabled 24 paleomagnetic collections (536 sites, 6547 specimens) to be made in the northern Cordillera. Paleopoles from 16 studies are integrated with other published paleopoles to present a tectonic synthesis for the Intermontane Belt (IMB) and YukonTanana (YT) terranes since 215 Ma. It shows that the YT terrane has been parautochthonous with the North American craton at least since the Early Jurassic. Since 54 Ma the IMB terranes have rotated steadily clockwise at 0.29° ± 0.11°/Ma on top of the YT terrane and craton or by 16° ± 6° clockwise. Between 102 ± 14 and 54 Ma, the IMB terranes rotated another 35° ± 14° clockwise, probably during Paleocene collision with the craton, and were translated 8.3° ± 7.0° (2σ) (915 ± 775 km) northward, probably during the Late Cretaceous on the Kula plate. The 915 km estimate is much less than most paleomagnetic estimates for "Baja BC" but agrees with the geological evidence. These post-Jurassic estimates are used to reconstruct the position of the Late Triassic  Jurassic cratonic apparent polar wander path for the IMB. The resulting IMB path is found to be concordant with the Cache Creek and Quesnellia terrane poles, indicating that these terranes were together and close to the craton in the Early Jurassic. These results place the IMB terranes close to the Pacific coastline of the northern USA and southern Canada but rotated 35° ± 14° counterclockwise, in the Jurassic and Early Cretaceous.
Origin of Recent alkaline lavas by lithospheric thinning beneath the northern Canadian Cordillera
Authors: Abraham Anne-Claude , Francis Don , Polvé Mireille
Published: October 2005

Recent alkaline lavas that have erupted across the disparate terranes of the northern Canadian Cordillera provide natural probes with which to interrogate the underlying lithosphere. The lavas range between two compositional end members, olivine nephelinite (NEPH) and hypersthene-normative olivine (Hy-NORM) basalt. The chemical signature of amphibole in the incompatible element enriched NEPH end member indicates that it is derived in the lithospheric mantle. The Hy-NORM end member is characterized by lower incompatible trace element contents but is still relatively enriched relative to primitive mantle. Although the Hy-NORM end member is always more radiogenic in Pb and Sr isotopes and less radiogenic in Nd isotopes than the NEPH end member, its isotopic signature varies with tectonic belt. In particular, Hy-NORM basalts in the Omineca Belt are strikingly more radiogenic in Sr and Pb isotopes and less radiogenic in Nd isotopes than otherwise equivalent Hy-NORM basalts in the adjacent Intermontane Belt, indicating the existence of a major lithospheric boundary between the two belts. Cordilleran and other continental Hy-NORM basalts have distinctly low Ca and high Na contents compared with their equivalents in oceanic hot spots or at mid-ocean ridges. A comparison with experimental melts of mantle peridotite indicates that these characteristics reflect smaller degrees of partial melting (<10%) in the stability field of garnet in the lower lithospheric mantle beneath the northern Cordillera. Contrary to the conclusion commonly drawn from experimental results, the Cordilleran NEPH lavas may be derived from similar or shallower depths than coeval Hy-NORM basalts.
Crustal structure across the northern Cordillera, Yukon Territory, from seismic wide-angle studies: Omineca Belt to Intermontane Belt
Authors: Creaser Brian , Spence George
Published: October 2005

A seismic refraction  wide-angle reflection experiment shot in 1997 in the southern Yukon Territory crosses the Omineca Belt, which includes the strike-slip Tintina Fault, and terminates within the Intermontane Belt of the northern Canadian Cordillera. Lithospheric structure is interpreted from two-dimensional forward and inverse modelling of traveltimes, combined with forward-amplitude modelling, and from 2.5-dimensional modelling of gravity data. Beneath the Cassiar terrane and the North America miogeocline, average velocities in the upper 20 km of crust are < 6.1 km/s. In the west beneath the accreted Cache Creek, Slide Mountain, and YukonTanana terranes, average velocities increase to ∼6.3 km/s. In the upper crust, the velocity model beneath these terranes thus correlates with more mafic accreted material and not with a subsurface extension of the Cassiar terrane. The Tintina Fault is a crustal-scale structure across which significant structural differences occur. A mid-crustal reflector terminates to the east of the Tintina Fault. The crust immediately west of the fault is thicker (∼37 km) than the crust to the east (∼34 km); the thick crust may suggest movement along the fault from a region of thicker crust to the south. Lower crustal velocities range from 6.4 to 6.7 km/s, with the lowest velocities located 2550 km west of the Tintina Fault, coincident with the location of the thickest crust. A reflector at 28 km depth may correspond to the top of Proterozoic cratonic basement in the lowermost crust. Upper mantle velocities just below the Moho range from 7.8 to 7.9 km/s, consistent with the high heat flow in the region.
105 Million years of igneous activity, Wrangell, Alaska, to Prince Rupert, British Columbia
Authors: Crawford Maria Luisa , Crawford William A , Lindline Jennifer
Published: October 2005

The Coast Mountains orogen, which lies along coastal British Columbia and southeastern Alaska, records extensive Mesozoic and Cenozoic igneous activity. Here we focus on the two youngest periods: 10550 Ma and 30 Ma  present. The history of subduction, orogen uplift, and, finally, extension associated with this magmatic activity can be related to plate motion since the mid-Cretaceous. The 10550 Ma period is related to terrane accretion and subduction. The northwestsoutheast-trending Coast shear zone divides the resulting Coast Mountains calc-alkaline continental margin batholith into a western (10590 Ma) and an eastern (8050 Ma) arc. Melting of hydrous mantle overlying a dehydrating slab generated the plutons of the western arc. The plutons of the eastern arc show a wider range of compositions. Their origin consists of mantle melts modified by melts from lower crustal rocks of continental affinity and possibly amphibolitic hydrated basalt. In both parts of the arc, igneous bodies also resulted from crustal melting; these are very abundant in the eastern arc. During the younger period bi-modal igneous suites consisting of mantle-derived mafic magmas and coeval crustal melts are associated with crustal extension and block faulting.
Current tectonics of the northern Canadian Cordillera
Authors: Hyndman Roy D , Flück Paul , Mazzotti Stephane , Lewis Trevor J , Ristau John , Leonard Lucinda
Published: October 2005

The northern Canadian Cordillera is remarkably tectonically and seismically active, extending from a terrane collision zone on the continental margin to an active fold and thrust belt at the eastern mountain front. The source and distribution of the deformation are constrained by (i) precision global positioning system (GPS) measurements; (ii) the seismicity distribution, mechanisms, and rates; (iii) the thermal regime; (iv) estimates of lithosphere thickness and strength; and (v) topography and gravity. The ongoing oblique collision of the Yakutat block in the northeast corner of the Gulf of Alaska has produced large deformation and uplift in the adjacent Saint Elias and Chugach mountains and appears to be responsible for the current deformation 800 km to the northeast. Northern Cordillera GPS velocities are ∼5 mm/year northeast relative to the North American Craton. Deformation rates across the eastern mountain front from earthquake statistics are similar, i.e., ∼4 mm/year of thrust shortening across the Mackenzie Mountains and right-lateral strike-slip in the Richardson Mountains. This large-scale motion is explained by a quasi-rigid displacement of the upper crust over a lower crust detachment. The detachment zone is a consequence of the high temperature of the northern Cordillera lithosphere and a weak eastern Cordillera deformation front. Regional Moho temperatures of 800950 °C are indicated by very high heat flow and other indicators of deep temperature and by the thin lithosphere effective thickness (Te). The northern Cordillera model may have application in other areas, such as the earlier thrusting in the southern Canadian Rocky Mountains driven by terrane collision along the Pacific margin.
Tectonic significance of potential-field anomalies in western Canada: results from the Lithoprobe SNORCLE transect
Authors: Lynn C Elissa , Cook Frederick A , Hall Kevin W
Published: October 2005

Potential-field anomalies within the Lithoprobe SNORCLE (Slave  Northern Cordillera Lithospheric Evolution) transect area provide geometrical constraints for regional crustal and lithospheric structures, as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles. Areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections, and forward modelling provides tests of different interpretations of deep (crustal and upper mantle) density structures. In a key result from modelling, a Paleoproterozoic subduction zone beneath the Wopmay orogen probably consists of high-density rocks, such as eclogite, within the upper mantle. This result supports the concept of moderate- to low-angle intra-lithospheric sutures. On an even larger scale, applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus provide means to track patterns across structural grain. For example, gravity and magnetic trends that are associated with Precambrian rocks of the Canadian Shield can, in some cases, be followed across much of the Cordillera. This result is consistent with North American Precambrian rocks composing much of the crust in the Cordillera and thus that the addition of "new" lithosphere during Mesozoic  early Tertiary accretion has been relatively minor.
The edge of northwestern North America at ∼1.8 Ga
Authors: Cook Frederick A , Hall Kevin W , Lynn C Elissa
Published: October 2005

The ∼1.80 Ga edge of the northwestern North American craton is buried beneath Phanerozoic and Proterozoic rocks of the Western Canada Sedimentary Basin and the adjacent Cordillera. It is visible in more than eight deep seismic reflection profiles that have images of west-facing crustal-scale monoclines with up to 1520 km of vertical relief, and it produces regional isostatic gravity anomalies that can be followed for more than 1500 km along strike. The deep reflection profiles include two major transects of Lithoprobe (southern Canadian Cordillera transect and Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) transect) and industry profiles that are strategically located to provide depth and geometry constraints on the monoclines. The isostatic anomalies mark the density transition from Paleoproterozoic and older crystalline rocks of the Canadian Shield to less dense supracrustal rocks of westward-thickening late Paleo proterozoic and younger strata. These gravity anomaly patterns thus provide areal geometry of crustal structure variations along strike away from the depth control provided by the seismic data. Although many of the monoclines follow the Fort Simpson geophysical trend along the Cordilleran deformation front, isostatic anomalies near Great Bear Lake delineate a northeast-striking region of low values that may coincide with a failed rift arm or the southern margin of a large basin. The monoclines are interpreted as a series of en echelon structures that probably formed as a result of lithospheric extension at about 1.801.70 Ga following terminal accretion of the Paleoproterozoic Wopmay Orogen.
Geoelectric structure of the Proterozoic Wopmay Orogen and adjacent terranes, Northwest Territories, Canada
Authors: Wu Xianghong , Ferguson Ian J , Jones Alan G
Published: October 2005

Magnetotelluric (MT) soundings were made along a transect in northern Canada crossing the Proterozoic Wopmay Orogen, Fort Simpson basin, and adjacent parts of the Slave craton and the Nahanni terrane. The results are used to define the geoelectric structure and constrain the crustal and lithospheric structure and evolution. Across the Wopmay Orogen, geoelectric strikes at crustal depths average N34°E and are interpreted to be related to transcurrent faulting that occurred during late distal collisions at the western margin of the orogen. Weak two-dimensionality in the Fort Simpson basin is interpreted to be due to the sedimentary rocks in the basin. At longer periods, geoelectric strikes across the Wopmay Orogen rotate from ∼N43°E at uppermost mantle penetration to ∼N62°E at a depth of 100 km. The uppermost mantle strikes are interpreted to be due to ductile shearing linked to the transcurrent faulting in the overlying crust. The deeper strikes may be caused by shearing at the base of the present-day lithosphere. Within the Wopmay Orogen, the MT results image a conductor at the margin of the Fort Simpson and Hottah terranes interpreted to be related to the collision of these terranes. Conductive crust beneath the western margin of the Great Bear magmatic arc suggests correlative rocks of the Coronation margin extend south of the Slave craton. Lastly, decreased resistivity in the Hottah terrane at mantle depths is interpreted to be caused by the introduction of graphitic or sulphidic rocks during subduction prior to the HottahSlave and Fort Simpson  Hottah collisions.
Neoarchean decoupling of upper- and mid-crustal tectonothermal domains in the southeast Slave Province: evidence from the Walmsley Lake area
Authors: Cairns S , Relf C , MacLachlan K , Davis W J
Published: October 2005

The Walmsley Lake area of the southeastern Slave Province, Northwest Territories, exposes a crustal transect from greenschist through to upper amphibolite facies. Two tectonothermal crustal domains are proposed based on disparate tectonic histories and rock types. Within the upper tectonothermal domain, D1 deformation reached lower amphibolite facies prior to 2614 Ma and associated M1 metamorphic conditions outlasted D1. Peak M2 conditions reached middle amphibolite facies prior to 2603 Ma and outlasted D2 deformation. Deformation style and metamorphic sequencing during these two pre-2600 Ma events are consistent with regional crustal shortening and thickening in the upper tectonothermal domain. At mid-crustal levels in the lower tectonothermal domain, a third tectonothermal event (D3M3) produced uppermost amphibolite-facies peak metamorphic conditions, transposed preexisting fabrics to shallow dips, and produced a subhorizontal foliation and recumbent folds at ca. 2583 Ma. D3 structures are not present in the upper tectono thermal domain, however, evidence of M3 heating is locally displayed in rocks at the base of the upper tectonothermal domain. Upper and lower domains were structurally decoupled during the D3M3 event. In rare places where the zone between the two domains outcrops, it comprises a narrow high-strain zone. The metamorphic and structural topology of the Walmsley Lake area is consistent with the topology predicted from thermomechanical modeling and modern observations of gravitational accommodation in structurally thickened crust.
The electrical resistivity structure of Archean to Tertiary lithosphere along 3200 km of SNORCLE profiles, northwestern Canada
Authors: Jones Alan G , Ledo Juanjo , Ferguson Ian J , Farquharson Colin , Garcia Xavier , Grant Nick , McNeice Gary , Roberts Brian , Spratt Jessica , Wennberg Grant , Wolynec Lisa , Wu Xianghong
Published: October 2005

Magnetotelluric (MT) measurements to image the three-dimensional resistivity structure of the North American continent from an Archean core to a region of Tertiary assembly were recorded at almost 300 sites along 3200 km of profiles on the Lithoprobe Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) transect in northwestern Canada. At the largest scale, the MT results indicate significant lithospheric thickness variation, from 260 km at the southwest margin of the Slave craton to significantly < 100 km at the southwestern end of the SNORCLE transect in the Cordillera. At intermediate scale, the resistivity results allow broad terrane subdivisions to be made. Several anomalously conductive zones along the SNORCLE transect, in rocks ranging in age from Archean to Tertiary, are attributed to the introduction of either water or carbon into the crust and mantle during subduction processes. At the local scale, the MT data image two major faults crossing the study area, the Great Slave Lake shear zone and the Tintina Fault. The resistivity images show that both the Tintina Fault and Great Slave Lake shear zone form crustal-scale features, and that the Tintina Fault has a remarkably uniform resistivity signature over a 400 km strike length in the study area. Arguably the most controversial conclusion reached is that the MT data do not support the western extension of North American autochthonous basement suggested from interpretation of the seismic reflection data.
Studying the spatiotemporal variation of the littoral fish community in a large prealpine lake, using self-organizing mapping
Authors: Reyjol Yorick , Fischer Philipp , Lek Sovan , Rösch Roland , Eckmann Reiner
Published: October 2005

One of the most fundamental feature of freshwater systems is the spatiotemporal structure of their communities. In the present study, we used an artificial neural network model, i.e., self-organizing mapping, together with a likelihood ratio χ2statistic for proportions to investigate the influence of each factor of a complex sampling scheme (i.e., site, year, month, and time of day) on the littoral fish community of Lake Constance (south Germany). Based on self-organizing mapping, four clusters of samples were defined characterized by distinct fish communities. The samples gathered in clusters 1 and 2 were significantly related to the factors month and time of the day, while those in cluster 3 were related to the factors month and site and those in cluster 4 to each of the four factors. The results are discussed with regard to the temporal patterns of species succession in lakes and their similarities with the spatial patterns observable in streams, the importance of plasticity with regard to the fish nycthemeral preferences, the partitioning of habitat at a large spatial scale and its importance for the coexistence of species, and the effects of the reoligotro phica tion process in lakes.
When fish meet a trawling vessel: examining the behaviour of gadoids using a free-floating buoy and acoustic split-beam tracking
Authors: Handegard N O , Tjøstheim D
Published: October 2005

The reaction of individual gadoids to a bottom-trawling vessel has been observed in situ in the Barents Sea using a free-floating buoy and acoustic target-tracking methods. More than 20 000 tracks were analysed in terms of velocity changes in vertical, athwarthship, and alongship direction relative to the vessel, the warps, and the trawl, respectively. The fish starts diving about 15 min before vessel passing. This coincides with the time the trawl is running and not with the gradual increase in vessel noise caused by the approaching vessel. The change in horizontal movement is more gradual and is directed away from the vessel in the alongship direction, but towards the vessel in the athwarthship direction. The strongest and sharpest response is related to the trawl warps. A strong herding in front of the warps is seen. Closer to the bottom, an athwarthship herding reaction is seen away from the trawl doors or possibly the lower parts of the warps. There were only minor differences when grouping the tracks according to light level, fish size, and fish density.
Reach-scale effects of riparian forest cover on urban stream ecosystems
Authors: Roy Allison H , Faust Christina L , Freeman Mary C , Meyer Judith L
Published: October 2005

We compared habitat and biota between paired open and forested reaches within five small streams (basin area 1020 km2) in suburban catchments (9%49% urban land cover) in the Piedmont of Georgia, USA. Stream reaches with open canopies were narrower than forested reaches (4.1 versus 5.0 m, respectively). There were no differences in habitat diversity (variation in velocity, depth, or bed particle size) between open and forested reaches. However, absence of local forest cover corresponded to decreased large wood and increased algal chlorophyll a standing crop biomass. These differences in basal food resources translated into higher densities of fishes in open (9.0 individuals·m2) versus forested (4.9 individuals·m2) reaches, primarily attributed to higher densities of the herbivore Campostoma oligolepis. Densities of terrestrial invertebrate inputs were higher in open reaches; however, trends suggested higher biomass of terrestrial inputs in forested reaches and a corresponding higher density of terrestrial prey consumed by water column feeding fishes. Reach-scale biotic integrity (macroinvertebrates, salamanders, and fishes) was largely unaffected by differences in canopy cover. In urbanizing areas where catchment land cover drives habitat and biotic quality, management practices that rely exclusively on forested riparian areas for stream protection are unlikely to be effective at maintaining ecosystem integrity.
Retention of juveniles within a hybrid zone between North Sea and Baltic Sea Atlantic cod (Gadus morhua)
Authors: Nielsen Einar E , Grønkjær Peter , Meldrup Dorte , Paulsen Helge
Published: October 2005

Elucidating the relative roles of dispersal and retention of juvenile stages is an important issue for understanding population structure and evolution in marine organisms. We investigated the genetic population structure of juvenile Atlantic cod (Gadus morhua) within the transition zone between the North Sea and the Baltic Sea, employing nine microsatellite loci, and compared our data with adult cod data from the same area. Small but statistically significant overall differentiation (Fst = 0.003) was found among juvenile samples. Samples of juveniles grouped genetically with adult samples from the same geographical regions. Individual admixture analysis of a large sample of juveniles taken within the transition zone showed that the patterns of genetic differentiation could not be explained by mixing of pure North Sea and Baltic Sea individuals. Instead, the high number of juveniles with intermediate genotypes was compatible with a scenario of exclusive local (transition zone) origin. The results support the hypothesis that population structure in marine fishes is maintained by the retention of juveniles.
Using tree-ring crossdating techniques to validate annual growth increments in long-lived fishes
Authors: Black Bryan A , Boehlert George W , Yoklavich Mary M
Published: October 2005

We applied crossdating, a dendrochronology (tree-ring analysis) age validation technique, to growth increment widths of 50 Sebastes diploproa otoliths ranging from 30 to 84 years in age. Synchronous growth patterns were matched by the following: (i) checking the dates of conspicuously narrow growth increments for agreement among samples and (ii) statistically verifying that growth patterns correlated among samples. To statistically verify pattern matching, we fit each time series of otolith measurements with a spline, and all measurements were divided by the values predicted by the curve. This standardized each time series to a mean of 1, removing the effects of age on growth and homogenizing variance. Each time series was then correlated with the average growth patterns of all other series, yielding an average correlation coefficient (r) of 0.53. Average growth of all 50 samples was significantly correlated with an upwelling index (r = 0.40, p = 0.002), the Pacific Decadal Oscillation (r = 0.29, p = 0.007), and the Northern Oscillation Index (r = 0.51, p = 0.0001), corroborating accuracy. We believe this approach to age validation will be applicable to a wide range of long-lived marine and freshwater species.
Species separation and zoogeography of redfish and rockfish (genus Sebastes) by otolith shape analysis
Authors: Stransky Christoph , MacLellan Shayne E
Published: October 2005

Interspecific otolith shape variation was investigated within the species-rich genus Sebastes (redfish, rockfish) as a tool for species separation, since morphological distinction has proven to be difficult. Otolith samples from all four North Atlantic redfish species, six commercially important rockfish species from the North Pacific, and Sebastes capensis from the South Atlantic were compared for differences in linear otolith measurements and elliptical Fourier-shape descriptors. A clear distinction between the North Atlantic and North Pacific / South Atlantic species (97% correct jackknifed classification) was achieved by univariate measurements and discriminant analysis of size-corrected Fourier descriptors. Overall species classification success was 91%, 94% within the North Pacific species and 88% within the North Atlantic samples. From the Pacific rockfish, Sebastes alutus otoliths showed the strongest affinity to the North Atlantic Sebastes. High similarity of otolith shapes of S. capensis to the North Pacific Sebastes and clear discrimination from North Atlantic species coincide with current zoogeographical and speciation theories, as well as with recently reported genetic results.
Modelling the invasion risk of diapausing organisms transported in ballast sediments
Authors: Wonham Marjorie J , Bailey Sarah A , MacIsaac Hugh J , Lewis Mark A
Published: October 2005

Biological invasions via ship ballast are a major driver of biodiversity change in aquatic systems. In the Laurentian Great Lakes basin, unique shipping operations pose a particular invasion risk. The majority (>90%) of incoming vessels are not fully loaded with ballast water but carry ballast sediments and residual water. Ballast sediments contain viable diapause organisms that could hatch and be released during routine ballast operations. To assess invasion risk and control of this pathway, we constructed and parameterized a dynamic hatching model for three representative groups of freshwater organisms that undergo diapause: rotifers, cladocerans, and copepods. Numerical model simulations show that ballast sediment is a plausible invasion pathway for all three groups. The model also illustrates that postuptake ballast treatment to remove or kill potential invaders should be applied as late as possible prior to deballasting to minimize the number of live organisms released. Simulations show that the ability of taxa to reproduce parthenogenetically inside a ballast tank greatly influences quantitative predictions of both risk and control.
Foraging by a young-of-the-year piscivore: the role of predator size, prey type, and density
Authors: Galarowicz Tracy L , Wahl David H
Published: October 2005

Young-of-the-year piscivores undergo ontogenetic diet shifts, but mechanisms influencing prey selection and implications for growth are unclear. We examined foraging and growth of 20- to 150-mm walleye (Sander vitreus) fed either zooplankton, benthic invertebrates, or fish over a range of prey densities in the laboratory. The number of each prey type consumed was influenced by walleye size and prey density. Walleye exhibited type II functional responses on each prey type; attack coefficients were constant across zooplankton and fish densities but decreased with benthic invertebrate densities. Handling time estimates were greater for fish than for other prey types but similar for zooplankton and benthos. Foraging efficiencies on zooplankton and benthic invertebrates increased with walleye size but were variable for fish prey. The smallest walleye size class (20 mm) had similar energy return (J·min1) and growth (g·day1) on zooplankton, benthic invertebrates, and fish. For larger walleye, both energy return and growth were highest on fish, intermediate on benthic invertebrates, and lowest on zooplankton. Diet shifts of juvenile piscivores and, consequently, growth can be explained by ontogenetic changes in foraging abilities and prey densities.
Interaction and dynamical binding of spin waves or excitons in quantum Hall systems
Authors: Wójs A , Gładysiewicz A , Wodziński D , Quinn J J
Published: October 2005

Interaction between spin waves (or excitons) moving in the lowest Landau level is studied using numerical diagonalization. Because of complicated statistics obeyed by these composite particles, their effective interaction is completely different from the dipoledipole interaction predicted in the model of independent (bosonic) waves. In particular, spin waves moving in the same direction attract one another, which leads to their dynamical binding. Effective interaction pseudopotentials V↑↑(k) and V↑↓(k) for two spin waves with equal wave vectors k and moving in the same or opposite directions are calculated and shown to obey power laws V(k) ∝ kα at small k. A high value of α↑↑ ≈ 4 explains the occurrence of linear bands in spin excitation spectra of quantum Hall droplets. PACS Nos.: 71.10.Pm, 71.35.y, 75.30.Ds
Nonplanar graphs and anomalies in chiral noncommutative gaugetheories
Authors: Gagne-Portelance Marie , McKeon D.G.C.
Published: October 2005

The AV (n) one-loop graphs are examined in a 2n-dimensional massless noncommutative gauge model in which both a U(1) axial gauge field A and a U(1) vector gauge field V have adjoint couplings to a Fermion field. A possible anomaly in the divergence of the n + 1 vertices is examined by considering the surface term that can possibly arise when shifting the loop momentum variable of integration. It is shown that despite the fact that the graphs are nonplanar, surface terms do arise in individual graphs, but that in 4n dimensions, a cancellation between the surface term contribution coming from pairs of graphs eliminates all anomalies, while in 4n + 2 dimensions such a cancellation cannot occur and an anomaly necessarily arises.PACS No.: 11.30.Rd
Effect of the modulation duty cycle on the amplitude of photoreflectance
Authors: Al-Arfaj Esam , Glosser R , Alavi Kambiz , Beam III E A
Published: October 2005

We have observed the behavior of photoreflectance (PR) spectra from a set of a molecular-beam-epitaxy-grown heterostructures as a function of the modulation duty cycle. This was done over a range of frequencies extending from 101000 Hz. By varying the duty cycle of the pump beam at different frequencies, we are able to find the duty cycle that gave the largest amplitude. While standard PR techniques use a 50% duty cycle, we have found that at low frequencies (1030 Hz) the optimal value is between 3040% in these particular sets of experiments resulting in as much as a 33% increase in amplitude. The change in the optimal values of the duty cycle from sample to sample was qualitatively correlated to the deep levels sample. PACS Nos.: 78.20.Ci, 78.40., 78.40.Fy
An historical overview of cavity-enhanced methods
Authors: Paldus Barbara A , Kachanov Alexander A
Published: October 2005

An historical overview of laser-based, spectroscopic methods that employ high-finesse optical resonators is presented. The overview begins with the early work in atomic absorption (1962) and optical cavities (1974) that led to the first mirror reflectivity measurements in 1980. This paper concludes with very recent extensions of cavity-enhanced methods for the study of condensed-phase media and biological systems. Methods described here include cavity ring-down spectroscopy, integrated cavity output spectroscopy, and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Given the explosive growth of the field over the past decade, this review does not attempt to present a comprehensive bibliography of all work published in cavity-enhanced spectroscopy, but rather strives to illustrate the rich history, creative diversity, and broad applications potential of these methods. PACS No.: 39.30.+w
Thin-layer effects on the CPT qc measurement
Authors: Ahmadi M M , Robertson P K
Published: October 2005

A numerical analysis is presented to model the cone penetration test (CPT) tip resistance in layered soil. Analyses are performed for two-layer soils composed of either sands with different relative densities or different materials (sand and clay). Parametric numerical modeling is used to determine the distance that a cone senses a new upcoming soil layer interface or a layer interface behind. Analyses are also carried out for a thin sand layer embedded in soft clay. It is seen that the full tip resistance may not be reached in thin stiff layers. This is especially true for penetration in thin dense sand layers interbedded in softer clay. A correction factor is suggested to correct the cone tip resistance in thin sand layers. The higher the stiffness and the thinner the layer, the larger the correction factor. The numerical results obtained in this paper are in good agreement with experimental observations. Some limitations of a previously proposed correction factor are discussed.Key words: cone tip resistance, modeling, sand, clay, interface influence distance, layering.