940 research outputs found
Evidence for anthropogenic <sup>14</sup>C-enrichment in estuarine waters adjacent to the North Sea
[1] The isotopic composition (d13C and D14C) of high
molecular weight dissolved organic carbon (HMW DOC)
was studied in the Tyne and Tweed estuaries, NE England.
Despite significant removal of terrigenous HMW DOC in
the low salinity regions (S < 15), D14C remained modern
with little variation around 115%. This lack of apparent age
discrimination was attributed to either non-oxidative
removal or the absence of a significant proportion of old
refractory C in the HMW DOC pool. At S < 15, we
observed seaward increases in d13C and D14C. With no
documented local 14C inputs, we attributed non-bomb
related 14C-enrichment at S < 15 to a possible âlingering
effectâ of distal anthropogenic sources in near-coastal North
Sea HMW DOC. Given the global distribution of potential
sources, we propose that anthropogenic 14C should be
considered in assigning ages of DOC pools in near-coastal
waters and suggest its possible use as a tracer for DOC
transformations
Effects of Fish Populations on Pacific Loon (Gavia pacifica) and Yellow-billed Loon (G. adamsii) Lake Occupancy and Chick Production in Northern Alaska
Predator populations are vulnerable to changes in prey distribution or availability. With warming temperatures, lake ecosystems in the Arctic are predicted to change in terms of hydrologic flow, water levels, and connectivity with other lakes. We surveyed lakes in northern Alaska to understand how shifts in the distribution or availability of fish may affect the occupancy and breeding success of Pacific (Gavia pacifica) and Yellow-billed Loons (G. adamsii). We then modeled the influence of the presence and abundance of five fish species and the physical characteristics of lakes (e.g., hydrologic connectivity) on loon lake occupancy and chick production. The presence of Alaska blackfish (Dallia pectoralis) had a positive influence on Pacific Loon occupancy and chick production, which suggests that small-bodied fish species provide important prey for loon chicks. No characteristics of fish species abundance affected Yellow-billed Loon lake occupancy. Instead, Yellow-billed Loon occupancy was influenced by the physical characteristics of lakes that contribute to persistent fish populations, such as the size of the lake and the proportion of the lake that remained unfrozen over winter. Neither of these variables, however, influenced chick production. The probability of an unoccupied territory becoming occupied in a subsequent year by Yellow-billed Loons was low, and no loon chicks were successfully raised in territories that were previously unoccupied. In contrast, unoccupied territories had a much higher probability of becoming occupied by Pacific Loons, which suggests that Yellow-billed Loons have strict habitat requirements and suitable breeding lakes may be limited. Territories that were occupied had high probabilities of remaining occupied for both loon species.
Les populations de prĂ©dateurs sont vulnĂ©rables aux changements de rĂ©partition ou de disponibilitĂ© des proies. En raison du rĂ©chauffement des tempĂ©ratures, on prĂ©voit que les Ă©cosystĂšmes lacustres de lâArctique changeront pour ce qui est du rĂ©gime hydrologique, des niveaux dâeau et de la connectivitĂ© avec dâautres lacs. Nous avons examinĂ© des lacs du nord de lâAlaska pour comprendre comment les changements en matiĂšre de rĂ©partition ou de disponibilitĂ© des poissons peuvent avoir des incidences sur le taux dâoccupation et sur le succĂšs de reproduction du huart du Pacifique (Gavia pacifica) et du huart Ă bec blanc (G. adamsii). Ensuite, nous avons modĂ©lisĂ© lâinfluence de la prĂ©sence et de lâabondance de cinq espĂšces de poissons de mĂȘme que les caractĂ©ristiques physiques de lacs (comme la connectivitĂ© hydrologique) par rapport au taux dâoccupation lacustre des huarts et Ă la production dâoisillons. La prĂ©sence du dallia (Dallia pectoralis) avait une influence positive sur lâoccupation et la production dâoisillons chez le huart du Pacifique, ce qui suggĂšre que les espĂšces de poissons au petit corps constituent une proie importante pour les oisillons. Aucune caractĂ©ristique de lâabondance des espĂšces de poissons nâa eu dâinfluence sur lâoccupation lacustre du huart Ă bec blanc. Lâoccupation du huart Ă bec blanc a plutĂŽt Ă©tĂ© influencĂ©e par les caractĂ©ristiques physiques des lacs qui contribuent aux populations de poissons persistantes, comme la taille du lac et la proportion du lac qui ne gelait pas en hiver. Toutefois, aucune de ces variables nâa exercĂ© dâinfluence sur la production dâoisillons. La probabilitĂ© quâun territoire inoccupĂ© devienne occupĂ© par le huart au bec blanc au cours dâune annĂ©e subsĂ©quente Ă©tait faible, et aucun oisillon huart nâa Ă©tĂ© Ă©levĂ© avec succĂšs dans des territoires dâoisillons anciennement inoccupĂ©s. En revanche, les territoires inoccupĂ©s avaient une beaucoup plus grande probabilitĂ© de devenir occupĂ©s par les huarts du Pacifique, ce qui suggĂšre que les huarts Ă bec blanc ont des exigences strictes en matiĂšre dâhabitat et que le nombre de lacs convenant Ă la reproduction risque dâĂȘtre limitĂ©. Les territoires qui Ă©taient occupĂ©s avaient de fortes probabilitĂ©s de rester occupĂ©s par les deux espĂšces de huarts
âDynamics of chromophoric dissolved organic matter in the Atlantic Ocean: unravelling province-dependent relationships, optical complexity, and environmental influencesâ
Copyright \ua9 2024 Sabbaghzadeh, Uher and Upstill-Goddard.We report on the spatial distributions and optical characteristics of chromophoric dissolved organic matter (CDOM) in the sea surface microlayer (SML), subsurface seawater (SSW), and water column profiles down to 500 m across a range of Atlantic Ocean biogeochemical provinces during two cruises of the UK Atlantic Meridional Transect program (AMT24 and AMT25). We measured the CDOM absorption coefficient at 300 nm, aCDOM(300), and determined CDOM spectral slopes across two UV wavelength ranges: S1 (275-295 nm) and S2 (350-400 nm). We used spectral slope ratios (SR: S1/S2) to infer CDOM source characteristics and transformation history. During both cruises, SML aCDOM(300) was highest in the Northern Hemisphere, particularly in the North Atlantic Drift Region (NADR). CDOM was always enriched in the SML, with enrichment factors (SML aCDOM(300) / SSW aCDOM(300)) ranging from 1.03 to 2.00, reflecting preferential accumulation of CDOM in the SML. We also found a significant inverse correlation between aCDOM(300) and S1 in both the SML (Spearmanâs rank correlation coefficient, r2 = -0.75, p < 0.001, n = 114) and water column profiles (r2 = -0.74, p < 0.001, n = 845). Biogeochemical province-dependent variations in the relationships between CDOM and chlorophyll a were also observed. In high-latitude regions, elevated aCDOM(300) and low SR values indicated a dominance of terrestrially-derived CDOM, whereas oligotrophic subtropical areas showed lower aCDOM(300) and higher SR values, suggestive of aged, refractory, and photodegraded biologically-derived CDOM. Taken together, these findings reveal a complexity of drivers affecting CDOM distributions and spectral properties, which may limit the use of CDOM in predictive relationships in the oceans. However, the potential use of chlorophyll a as a CDOM proxy may prove most successful in open ocean regions devoid of terrestrial inputs, where biological production predominates
Concept for a Time-of-Flight Small Angle Neutron Scattering Instrument at the European Spallation Source
A new Small Angle Neutron Scattering instrument is proposed for the European
Spallation Source. The pulsed source requires a time-of-flight analysis of the
gathered neutrons at the detector. The optimal instrument length is found to be
rather large, which allows for a polarizer and a versatile collimation. The
polarizer allows for studying magnetic samples and incoherent background
subtraction. The wide collimation will host VSANS and SESANS options that
increase the resolution of the instrument towards um and tens of um,
respectively. Two 1m2 area detectors will cover a large solid angle
simultaneously. The expected gains for this new instrument will lie in the
range between 20 and 36, depending on the assessment criteria, when compared to
up-to-date reactor based instruments. This will open new perspectives for fast
kinetics, weakly scattering samples, and multi-dimensional contrast variation
studies.Comment: 18 pages, 10 figure
Superconductivity in novel Ge-based skutterudites: {Sr,Ba}Pt_4Ge_{12}
Combining experiments and ab initio models we report on
and as members of a novel class of superconducting
skutterudites, where Sr or Ba atoms stabilize a framework entirely formed by
Ge-atoms. Below K, and 5.10 K for and , respectively, electron-phonon coupled superconductivity
emerges, ascribed to intrinsic features of the Pt-Ge framework, where Ge-
states dominate the electronic structure at the Fermi energy.Comment: 4 pages, 4 figures, accepted for publication in PR
The impact of phenotypic and genetic heterogeneity on results of genome wide association studies of complex diseases
Phenotypic misclassification (between cases) has been shown to reduce the power to detect association in genetic studies. However, it is conceivable that complex traits are heterogeneous with respect to individual genetic susceptibility and disease pathophysiology, and that the effect of heterogeneity has a larger magnitude than the effect of phenotyping errors. Although an intuitively clear concept, the effect of heterogeneity on genetic studies of common diseases has received little attention. Here we investigate the impact of phenotypic and genetic heterogeneity on the statistical power of genome wide association studies (GWAS). We first performed a study of simulated genotypic and phenotypic data. Next, we analyzed the Wellcome Trust Case-Control Consortium (WTCCC) data for diabetes mellitus (DM) type 1 (T1D) and type 2 (T2D), using varying proportions of each type of diabetes in order to examine the impact of heterogeneity on the strength and statistical significance of association previously found in the WTCCC data. In both simulated and real data, heterogeneity (presence of "non-cases") reduced the statistical power to detect genetic association and greatly decreased the estimates of risk attributed to genetic variation. This finding was also supported by the analysis of loci validated in subsequent large-scale meta-analyses. For example, heterogeneity of 50% increases the required sample size by approximately three times. These results suggest that accurate phenotype delineation may be more important for detecting true genetic associations than increase in sample size
Effects of partial substitution of Ni by Pd on the thermoelectric properties of ZrNiSn-based half-Heusler compounds
We report on the effects of partial substitution of nickel by palladium on the thermoelectric properties of ZrNiSn-based half-Heusler compounds. It is shown that the substitution of palladium for nickel results in a significant, beneficial reduction of the thermal conductivity. The Seebeck coefficient also decreases, but only by a small amount. In the Hf0.5Zr0.5Ni0.8Pd0.2Sn0.99Sb0.01Hf0.5Zr0.5Ni0.8Pd0.2Sn0.99Sb0.01 compound, a power factor of 22.1 ÎŒWâKâ2âcmâ1 and a thermal conductivity as low as 4.5 W/mâK are measured at room temperature. The dimensionless figure of merit ZT increases with increasing temperature and reaches a maximum value of 0.7 at about 800 K. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70206/2/APPLAB-79-25-4165-1.pd
Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting Films
We report observations of spontaneous formation of magnetic flux lines during
a rapid quench of YBaCuO films through T. This
effect is predicted according to the Kibble-Zurek mechanism of creation of
topological defects of the order parameter during a symmetry-breaking phase
transition. Our previous experiment, at a quench rate of 20K/sec, gave null
results. In the present experiment, the quench rate was increased to
\TEXTsymbol{>} 10 K/sec. Within experimental resolution, the dependence
of the measured flux on the cooling rate is consistent with the prediction
Impulsive light-scattering by coherent phonons in LaAlO3: Disorder and boundary effects
Pump-probe measurements of coherent-phonon-induced changes of refractive index in LaAlO3 are dominated by normally weak boundary effects. Atomic displacements in the range 50â500 Ό⫠were generated and probed by femtosecond laser pulses through impulsive Raman scattering. The absence of a bulk contribution is ascribed to phase mismatch due to domain disorder. Selection rules are consistent with a Raman model considering reflection and transmission at interfaces. Intensities and phonon parameters as a function of temperature agree well with incoherent Raman data
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