650 research outputs found
Synthesis of N-Heterocylic Carbene-Containing Metal Complexes from 2-(Pentafluorophenyl)imidazolidines
N-Heterocyclic carbene (NHC)-containing metal complexes are prepared through a simple, base-free method involving the decomposition of 2-(pentafluorophenyl)imidazolidines under mild thermolytic conditions. Ruthenium, iridium, and rhodium complexes containing NHC ligands with different electronic and steric parameters are reported
The Genome Sequence of the Metal-Mobilizing, Extremely Thermoacidophilic Archaeon \u3ci\u3eMetallosphaera sedula\u3c/i\u3e Provides Insights into Bioleaching-Associated Metabolism
Despite their taxonomic description, not all members of the order Sulfolobales are capable of oxidizing
reduced sulfur species, which, in addition to iron oxidation, is a desirable trait of biomining microorganisms.
However, the complete genome sequence of the extremely thermoacidophilic archaeon Metallosphaera sedula
DSM 5348 (2.2 Mb, _2,300 open reading frames [ORFs]) provides insights into biologically catalyzed metal
sulfide oxidation. Comparative genomics was used to identify pathways and proteins involved (directly or
indirectly) with bioleaching. As expected, the M. sedula genome contains genes related to autotrophic carbon
fixation, metal tolerance, and adhesion. Also, terminal oxidase cluster organization indicates the presence of
hybrid quinol-cytochrome oxidase complexes. Comparisons with the mesophilic biomining bacterium Acidithiobacillus
ferrooxidans ATCC 23270 indicate that the M. sedula genome encodes at least one putative rusticyanin,
involved in iron oxidation, and a putative tetrathionate hydrolase, implicated in sulfur oxidation. The
fox gene cluster, involved in iron oxidation in the thermoacidophilic archaeon Sulfolobus metallicus, was also
identified. These iron- and sulfur-oxidizing components are missing from genomes of nonleaching members of
the Sulfolobales, such as Sulfolobus solfataricus P2 and Sulfolobus acidocaldarius DSM 639. Whole-genome
transcriptional response analysis showed that 88 ORFs were up-regulated twofold or more in M. sedula upon
addition of ferrous sulfate to yeast extract-based medium; these included genes for components of terminal
oxidase clusters predicted to be involved with iron oxidation, as well as genes predicted to be involved with
sulfur metabolism. Many hypothetical proteins were also differentially transcribed, indicating that aspects of
the iron and sulfur metabolism of M. sedula remain to be identified and characterized
High-Resolution Infrared Spectroscopy of the Brown Dwarf Epsilon Indi Ba
We report on the analysis of high-resolution infrared spectra of the newly
discovered brown dwarf Epsilon Indi Ba. This is the closest known brown dwarf
to the solar system, with a distance of 3.626 pc. Spectra covering the ranges
of 2.308-2.317 microns and 1.553-1.559 microns were observed at a spectral
resolution of R=50,000 with the Phoenix spectrometer on the Gemini South
telescope. The physical paramters of effective temperature and surface gravity
are derived by comparison to model spectra calculated from atmospheres computed
using unified cloudy models. An accurate projected rotational velocity is also
derived.Comment: 9 pages, 3 figures. Astrophysical Journal Letters, in pres
Role of \u3ci\u3evapBC\u3c/i\u3e toxin–antitoxin loci in the thermal stress response of \u3ci\u3eSulfolobus solfataricus\u3c/i\u3e
TA (toxin–antitoxin) loci are ubiquitous in prokaryotic microorganisms, including archaea, yet
their physiological function is largely unknown. For example, preliminary reports have suggested
that TA loci are microbial stress-response elements, although it was recently shown that knocking
out all known chromosomally located TA loci in Escherichia coli did not have an impact on
survival under certain types of stress. The hyperthermophilic crenarchaeon Sulfolobus solfataricus
encodes at least 26 vapBC (where vap is virulence-associated protein) family TA loci in its
genome. VapCs are PIN (PilT N-terminus) domain proteins with putative ribonuclease activity,
while VapBs are proteolytically labile proteins, which purportedly function to silence VapCs when
associated as a cognate pair. Global transcriptional analysis of S. solfataricus heat-shock-response
dynamics (temperature shift from 80 to 90°C) revealed that several vapBC genes were triggered
by the thermal shift, suggesting a role in heat-shock-response. Indeed, knocking out a specific
vapBC locus in S. solfataricus substantially changed the transcriptome and, in one case, rendered
the crenarchaeon heat-shock-labile. These findings indicate that more work needs to be done to
determine the role of VapBCs in S. solfataricus and other thermophilic archaea, especially with
respect to post-transcriptional regulation
Role of \u3ci\u3evapBC\u3c/i\u3e toxin–antitoxin loci in the thermal stress response of \u3ci\u3eSulfolobus solfataricus\u3c/i\u3e
TA (toxin–antitoxin) loci are ubiquitous in prokaryotic microorganisms, including archaea, yet
their physiological function is largely unknown. For example, preliminary reports have suggested
that TA loci are microbial stress-response elements, although it was recently shown that knocking
out all known chromosomally located TA loci in Escherichia coli did not have an impact on
survival under certain types of stress. The hyperthermophilic crenarchaeon Sulfolobus solfataricus
encodes at least 26 vapBC (where vap is virulence-associated protein) family TA loci in its
genome. VapCs are PIN (PilT N-terminus) domain proteins with putative ribonuclease activity,
while VapBs are proteolytically labile proteins, which purportedly function to silence VapCs when
associated as a cognate pair. Global transcriptional analysis of S. solfataricus heat-shock-response
dynamics (temperature shift from 80 to 90°C) revealed that several vapBC genes were triggered
by the thermal shift, suggesting a role in heat-shock-response. Indeed, knocking out a specific
vapBC locus in S. solfataricus substantially changed the transcriptome and, in one case, rendered
the crenarchaeon heat-shock-labile. These findings indicate that more work needs to be done to
determine the role of VapBCs in S. solfataricus and other thermophilic archaea, especially with
respect to post-transcriptional regulation
Role of an Archaeal PitA Transporter in the Copper and Arsenic Resistance of \u3ci\u3eMetallosphaera sedula\u3c/i\u3e, an Extreme Thermoacidophile
Thermoacidophilic archaea, such as Metallosphaera sedula, are lithoautotrophs that occupy metal-rich environments. In previous studies, an M. sedula mutant lacking the primary copper efflux transporter, CopA, became copper sensitive. In contrast, the basis for supranormal copper resistance remained unclear in the spontaneous M. sedula mutant, CuR1. Here, transcriptomic
analysis of copper-shocked cultures indicated that CuR1 had a unique regulatory response to metal challenge corresponding to the upregulation of 55 genes. Genome resequencing identified 17 confirmed mutations unique to CuR1 that were likely to change gene function. Of these, 12 mapped to genes with annotated function associated with transcription, metabolism, or transport.
These mutations included 7 nonsynonymous substitutions, 4 insertions, and 1 deletion. One of the insertion mutations mapped to pseudogene Msed_1517 and extended its reading frame an additional 209 amino acids. The extended mutant allele was identified as a homolog of Pho4, a family of phosphate symporters that includes the bacterial PitA proteins. Orthologs of this allele
were apparent in related extremely thermoacidophilic species, suggesting M. sedula naturally lacked this gene. Phosphate transport studies combined with physiologic analysis demonstrated M. sedula PitA was a low-affinity, high-velocity secondary transporter implicated in copper resistance and arsenate sensitivity. Genetic analysis demonstrated that spontaneous arsenate-resistant mutants derived from CuR1 all underwent mutation in pitA and nonselectively became copper sensitive. Taken together, these results point to archaeal PitA as a key requirement for the increased metal resistance of strain CuR1 and its accelerated capacity for copper bioleaching
Domain Wall Fermions with Exact Chiral Symmetry
We show how the standard domain wall action can be simply modified to allow
arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note
that the method can be used for both quenched and dynamical calculations. We
test the method using smooth and thermalized gauge field configurations. We
also make comparisons of the performance (cost) of the domain wall operator for
spectroscopy compared to other methods such as the overlap-Dirac operator and
find both methods are comparable in cost.Comment: revtex, 37 pages, 11 color postscript figure
Status of light weight cassette design of SOFC
Lightweight SOFC stacks are currently being developed especially for automotive applications such as APU and for portable devices. Within the EU funded project MMLCR=SOFC the Jülich lightweight so-called CS-design was improved concerning better suitability for glass sealing, reduced manufacturing effort and increased power. Based on modelling in combination with manufacturing experience, test results, and post-test analysis substantial changes of the previous CS-design were made. The manufacturing of single parts, particularly due to the improved design of sheet metal interconnects, as well as the assembling processes are suitable for low-cost mass manufacturing. The novel decal concept of glass-ceramic sealant screen printed on foil in order to produce green tapes is used for joining the stack layers offering an enormous potential for cost savings in industrial assembly process. First stack tests with the new CSV–design showed a comparable electrochemical performance to the previous CSIV design having at the same time a better thermo-mechanical behavior.</jats:p
Stellar Iron Abundances at the Galactic Center
We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.Comment: 41 pages, 9 figures, ApJ, in pres
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Protecting Adolescents from Harm: Findings from the National Longitudinal Study on Adolescent Health.
Some children who are at highrisk for health-compromising behaviors successfully negotiate adolescence, avoiding the behaviors that predispose them to negative health outcomes; while others, relatively advantaged socially and economically, sustain significant morbidity as a consequence of their behaviors. These issues of vulnerability and resilience have stimulated an interest in the identification of protective factors in the lives of young people—factors that,if present, diminish the likelihood of negative health and social outcomes.20"26 Of the constellation of forces that influence adolescent health-risk behavior, the most fundamental are the social contexts in which adolescents are embed¬ded20;the family and school contexts are among the most critical. Yet, how adolescents' connections to these contexts shape their health-risk behaviors is poorly understood
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