7,125 research outputs found
Microbial and biogeochemical responses to projected future nitrate enrichment in the California upwelling system
Coastal California is a dynamic upwelling region where nitrogen (N) and iron (Fe) can both limit productivity and influence biogeochemistry over different spatial and temporal scales. With global change, the flux of nitrate from upwelling is expected to increase over the next century, potentially driving additional oceanic regions toward Fe limitation. In this study we explored the effect of changes in Fe/N ratio on native phytoplankton from five currently Fe-replete sites near the major California upwelling centers at Bodega Bay and Monterey Bay using nutrient addition incubation experiments. Despite the high nitrate levels (13–30 μ M) in the upwelled water, phytoplankton at three of the five sites showed increased growth when 10 μ M nitrate was added. None of the sites showed enhanced growth following addition of 10 nM Fe. Nitrate additions favored slow sinking single-celled diatoms over faster sinking chain-forming diatoms, suggesting that future increases in nitrate flux could affect carbon and silicate export and alter grazer populations. In particular, solitary cells of Cylindrotheca were more abundant than the toxin-producing genus Pseudonitzschia following nitrate addition. These responses suggest the biogeochemistry of coastal California could change in response to future increases in nitrate, and multiple stressors like ocean acidification and hypoxia may further result in ecosystem shifts
Insights on quorum-quenching properties of Lysinibacillus fusiformis strain RB21, a Malaysian municipal solid-waste landfill soil isolate, via complete genome sequence analysis
YesLysinibacillus fusiformis strain RB21 is a quorum-quenching bacterium that is able to degrade quorum-sensing signaling molecules. Here, we present the first complete genome sequence of L. fusiformis strain RB21. The finished genome is 4.8 Mbp in size, and the quorum-quenching gene was identified.University of Malaya for High Impact Research (UM-MOHE HIR) grant UM C/625/1/HIR/MOHE/CHAN/01, no. A000001-50001 and grant UM C/625/1/HIR/MOHE/CHAN/14/1, H-50001-A00002
Separation of Quasiparticle and Phononic Heat Currents in YBCO
Measurements of the transverse (k_{xy}) and longitudinal (k_{xx}) thermal
conductivity in high magnetic fields are used to separate the quasiparticle
thermal conductivity (k_{xx}^{el}) of the CuO_2-planes from the phononic
thermal conductivity in YBa_2Cu_3O_{7-\delta}. k_{xx}^{el} is found to display
a pronounced maximum below T_c. Our data analysis reveals distinct transport
(\tau) and Hall (\tau_H) relaxation times below T_c: Whereas \tau is strongly
enhanced, \tau_H follows the same temperature dependence as above T_c
Non-magnetic impurity scattering in a superconductor near a van Hove point: Zn versus Ni in the cuprates
We consider the effect of non-magnetic impurities in a
superconductor with \ef close to a van Hove singularity. It is shown that the
non-trivial density of states (DOS) allows for resonant scattering already at
intermediate potential strengths eV. The residual DOS at
\ef, and the \tc suppression rate are found to strongly depend on the carrier
concentration. Quantitative agreement with experiments on Zn and Ni doped
cuprates is obtained by adjusting a single parameter, .Comment: 4 pages uuencoded compressed Postscript (Minor changes
Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn
We report on the pressure dependence of the Hall coefficient in
quasi-2D heavy fermion CeCoIn. At ambient pressure, below a temperature
associated with the emergence of non-Fermi liquid properties, is
anomalously enhanced. We found that the restoration of the Fermi liquid state
with applied pressure leads to a gradual suppression of this dramatic
enhancement. Moreover, the enhancement in was found to be confined to an
intermediate temperature window, where inelastic electron-electron scattering
is dominant. Our results strongly support the presence of cold and hot spots on
the Fermi surface probably due to anisotropic scattering by antiferromagnetic
fluctuations, which may also prove relevant for the debate on the anomalous
normal-state properties of high- cuprates.Comment: 9 pages, 5 fiqures, to be published in J. Phys. Soc. Jp
Scaling of the anomalous Hall effect in SrCaRuO
The anomalous Hall effect (AHE) of ferromagnetic thin films of
SrCaRuO (0 0.4) is studied as a function of
and temperature . As increases, both the transition temperature
and the magnetization are reduced and vanish near 0.7. For all
compositions, the transverse resistivity varies non-monotonously
with , and even changes sign, thus violating the conventional expression
( is the magnetic induction, while
and are the ordinary and anomalous Hall coefficients). From the rather
complicated data of , we find a scaling behavior of the transverse
conductivity with , which is well reproduced by the
first-principles band calculation assuming the intrinsic origin of the AHE.Comment: REVTeX 4 style; 5 pages, 3 figures; revised 23/2 and accepted for
publicatio
Quasiparticle thermal Hall angle and magnetoconductance in YBa_2Cu_3O_x
We present a way to extract the quasiparticle (qp) thermal conductivity
Kappa_e and mean-free-path in YBa_2Cu_3O_x, using the thermal Hall effect and
the magnetoconductance of Kappa_e. The results are very consistent with heat
capacity experiments. Moreover, we find a simple relation between the thermal
Hall angle Theta_Q and the H-dependence of Kappa_e, as well as numerical
equality between Theta_Q and the electrical Hall angle. The findings also
reveal an anomalously anisotropic scattering process in the normal state.Comment: 4 pages in Tex, 5 figures in EPS; replaced on 5/12/99, minor change
Archiving scientific data
We present an archiving technique for hierarchical data with key structure. Our approach is based on the notion of timestamps whereby an element appearing in multiple versions of the database is stored only once along with a compact description of versions in which it appears. The basic idea of timestamping was discovered by Driscoll et. al. in the context of persistent data structures where one wishes to track the sequences of changes made to a data structure. We extend this idea to develop an archiving tool for XML data that is capable of providing meaningful change descriptions and can also efficiently support a variety of basic functions concerning the evolution of data such as retrieval of any specific version from the archive and querying the temporal history of any element. This is in contrast to diff-based approaches where such operations may require undoing a large number of changes or significant reasoning with the deltas. Surprisingly, our archiving technique does not incur any significant space overhead when contrasted with other approaches. Our experimental results support this and also show that the compacted archive file interacts well with other compression techniques. Finally, another useful property of our approach is that the resulting archive is also in XML and hence can directly leverage existing XML tools
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