1,029 research outputs found
Spontaneous separation of two-component Fermi gases in a double-well trap
The two-component Fermi gas in a double-well trap is studied using the
density functional theory and the density profile of each component is
calculated within the Thomas-Fermi approximation. We show that the two
components are spatially separate in the two wells once the repulsive
interaction exceeds the Stoner point, signaling the occurrence of the
ferromagnetic transition. Therefore, the double-well trap helps to explore
itinerant ferromagnetism in atomic Fermi gases, since the spontaneous
separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep
Emergence of magnetism in graphene materials and nanostructures
Magnetic materials and nanostructures based on carbon offer unique
opportunities for future technological applications such as spintronics. This
article reviews graphene-derived systems in which magnetic correlations emerge
as a result of reduced dimensions, disorder and other possible scenarios. In
particular, zero-dimensional graphene nanofragments, one-dimensional graphene
nanoribbons, and defect-induced magnetism in graphene and graphite are covered.
Possible physical mechanisms of the emergence of magnetism in these systems are
illustrated with the help of computational examples based on simple model
Hamiltonians. In addition, this review covers spin transport properties,
proposed designs of graphene-based spintronic devices, magnetic ordering at
finite temperatures as well as the most recent experimental achievements.Comment: tutorial-style review article -- 18 pages, 19 figure
Performance of a 229 Thorium solid-state nuclear clock
The 7.8 eV nuclear isomer transition in 229 Thorium has been suggested as an
etalon transition in a new type of optical frequency standard. Here we discuss
the construction of a "solid-state nuclear clock" from Thorium nuclei implanted
into single crystals transparent in the vacuum ultraviolet range. We
investigate crystal-induced line shifts and broadening effects for the specific
system of Calcium fluoride. At liquid Nitrogen temperatures, the clock
performance will be limited by decoherence due to magnetic coupling of the
Thorium nucleus to neighboring nuclear moments, ruling out the commonly used
Rabi or Ramsey interrogation schemes. We propose a clock stabilization based on
counting of flourescence photons and present optimized operation parameters.
Taking advantage of the high number of quantum oscillators under continuous
interrogation, a fractional instability level of 10^{-19} might be reached
within the solid-state approach.Comment: 28 pages, 9 figure
Novel laser spectroscopic technique for continuous analysis of N2O isotopomers - application and intercomparison with isotope ratio mass spectrometry
RATIONALE Nitrous oxide (N2O), a highly climate-relevant trace gas, is mainly derived from microbial denitrification and nitrification processes in soils. Apportioning N2O to these source processes is a challenging task, but better understanding of the processes is required to improve mitigation strategies. The N2O site-specific 15?N signatures from denitrification and nitrification have been shown to be clearly different, making this signature a potential tool for N2O source identification. We have applied for the first time quantum cascade laser absorption spectroscopy (QCLAS) for the continuous analysis of the intramolecular 15?N distribution of soil-derived N2O and compared this with state-of-the-art isotope ratio mass spectrometry (IRMS). METHODS Soil was amended with nitrate and sucrose and incubated in a laboratory setup. The N2O release was quantified by FTIR spectroscopy, while the N2O intramolecular 15?N distribution was continuously analyzed by online QCLAS at 1?Hz resolution. The QCLAS results on time-integrating flask samples were compared with those from the IRMS analysis. RESULTS The analytical precision (2 sigma) of QCLAS was around 0.3 parts per thousand for the delta 15Nbulk and the 15?N site preference (SP) for 1-min average values. Comparing the two techniques on flask samples, excellent agreement (R2?=?0.99; offset of 1.2 parts per thousand) was observed for the delta 15Nbulk values while for the SP values the correlation was less good (R2?=?0.76; offset of 0.9 parts per thousand), presumably due to the lower precision of the IRMS SP measurements. CONCLUSIONS These findings validate QCLAS as a viable alternative technique with even higher precision than state-of-the-art IRMS. Thus, laser spectroscopy has the potential to contribute significantly to a better understanding of N turnover in soils, which is crucial for advancing strategies to mitigate emissions of this efficient greenhouse gas. Copyright (c) 2012 John Wiley & Sons, Ltd
Pauli's Principle in Probe Microscopy
Exceptionally clear images of intramolecular structure can be attained in
dynamic force microscopy through the combination of a passivated tip apex and
operation in what has become known as the "Pauli exclusion regime" of the
tip-sample interaction. We discuss, from an experimentalist's perspective, a
number of aspects of the exclusion principle which underpin this ability to
achieve submolecular resolution. Our particular focus is on the origins,
history, and interpretation of Pauli's principle in the context of interatomic
and intermolecular interactions.Comment: This is a chapter from "Imaging and Manipulation of Adsorbates using
Dynamic Force Microscopy", a book which is part of the "Advances in Atom and
Single Molecule Machines" series published by Springer
[http://www.springer.com/series/10425]. To be published late 201
The Echinococcus canadensis (G7) genome: A key knowledge of parasitic platyhelminth human diseases
Background: The parasite Echinococcus canadensis (G7) (phylum Platyhelminthes, class Cestoda) is one of the causative agents of echinococcosis. Echinococcosis is a worldwide chronic zoonosis affecting humans as well as domestic and wild mammals, which has been reported as a prioritized neglected disease by the World Health Organisation. No genomic data, comparative genomic analyses or efficient therapeutic and diagnostic tools are available for this severe disease. The information presented in this study will help to understand the peculiar biological characters and to design species-specific control tools. Results: We sequenced, assembled and annotated the 115-Mb genome of E. canadensis (G7). Comparative genomic analyses using whole genome data of three Echinococcus species not only confirmed the status of E. canadensis (G7) as a separate species but also demonstrated a high nucleotide sequences divergence in relation to E. granulosus (G1). The E. canadensis (G7) genome contains 11,449 genes with a core set of 881 orthologs shared among five cestode species. Comparative genomics revealed that there are more single nucleotide polymorphisms (SNPs) between E. canadensis (G7) and E. granulosus (G1) than between E. canadensis (G7) and E. multilocularis. This result was unexpected since E. canadensis (G7) and E. granulosus (G1) were considered to belong to the species complex E. granulosus sensu lato. We described SNPs in known drug targets and metabolism genes in the E. canadensis (G7) genome. Regarding gene regulation, we analysed three particular features: CpG island distribution along the three Echinococcus genomes, DNA methylation system and small RNA pathway. The results suggest the occurrence of yet unknown gene regulation mechanisms in Echinococcus. Conclusions: This is the first work that addresses Echinococcus comparative genomics. The resources presented here will promote the study of mechanisms of parasite development as well as new tools for drug discovery. The availability of a high-quality genome assembly is critical for fully exploring the biology of a pathogenic organism. The E. canadensis (G7) genome presented in this study provides a unique opportunity to address the genetic diversity among the genus Echinococcus and its particular developmental features. At present, there is no unequivocal taxonomic classification of Echinococcus species; however, the genome-wide SNPs analysis performed here revealed the phylogenetic distance among these three Echinococcus species. Additional cestode genomes need to be sequenced to be able to resolve their phylogeny.Fil: Maldonado, Lucas Luciano. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Assis, Juliana. FundaciĂłn Oswaldo Cruz; BrasilFil: Gomes AraĂşjo, FlĂĄvio M.. FundaciĂłn Oswaldo Cruz; BrasilFil: Salim, Anna C. M.. FundaciĂłn Oswaldo Cruz; BrasilFil: Macchiaroli, Natalia. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Cucher, Marcela Alejandra. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Camicia, Federico. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Fox, Adolfo. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Rosenzvit, Mara Cecilia. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; ArgentinaFil: Oliveira, Guilherme. Instituto TecnolĂłgico Vale; Brasil. FundaciĂłn Oswaldo Cruz; BrasilFil: Kamenetzky, Laura. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂŠdica; Argentin
Genomic Prevalence of Heterochromatic H3K9me2 and Transcription Do Not Discriminate Pluripotent from Terminally Differentiated Cells
Cellular differentiation entails reprogramming of the transcriptome from a
pluripotent to a unipotent fate. This process was suggested to coincide with a
global increase of repressive heterochromatin, which results in a reduction of
transcriptional plasticity and potential. Here we report the dynamics of the
transcriptome and an abundant heterochromatic histone modification,
dimethylation of histone H3 at lysine 9 (H3K9me2), during neuronal
differentiation of embryonic stem cells. In contrast to the prevailing model, we
find H3K9me2 to occupy over 50% of chromosomal regions already in stem
cells. Marked are most genomic regions that are devoid of transcription and a
subgroup of histone modifications. Importantly, no global increase occurs during
differentiation, but discrete local changes of H3K9me2 particularly at genic
regions can be detected. Mirroring the cell fate change, many genes show altered
expression upon differentiation. Quantitative sequencing of transcripts
demonstrates however that the total number of active genes is equal between stem
cells and several tested differentiated cell types. Together, these findings
reveal high prevalence of a heterochromatic mark in stem cells and challenge the
model of low abundance of epigenetic repression and resulting global basal level
transcription in stem cells. This suggests that cellular differentiation entails
local rather than global changes in epigenetic repression and transcriptional
activity
Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics
A detailed study is presented of the expected performance of the ATLAS
detector. The reconstruction of tracks, leptons, photons, missing energy and
jets is investigated, together with the performance of b-tagging and the
trigger. The physics potential for a variety of interesting physics processes,
within the Standard Model and beyond, is examined. The study comprises a series
of notes based on simulations of the detector and physics processes, with
particular emphasis given to the data expected from the first years of
operation of the LHC at CERN
Low NO and variable CH fluxes from tropical forest soils of the Congo Basin
Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (NO) and sink for methane (CH). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ NO and CH flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (nâ=â1558) and riverine dissolved gas concentration (nâ=â332) measurements spanning montane, swamp, and lowland forests. Each forest type core monitoring site was sampled at least for one hydrological year between 2016 - 2020 at a frequency of 7-14 days. We estimate a terrestrial CH uptake (in kg CH-C ha yr) for montane (â4.28) and lowland forests (â3.52) and a massive CH release from swamp forests (non-inundated 2.68; inundated 341). All investigated forest types were a NO source (except for inundated swamp forest) with 0.93, 1.56, 3.5, and â0.19âkg NO-N ha yr for montane, lowland, non-inundated swamp, and inundated swamp forests, respectively
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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