3,005 research outputs found
Spin Coherence and N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR
Pulsed ESR experiments are reported for ensembles of negatively-charged
nitrogen-vacancy centers (NV) in diamonds at X-band magnetic fields
(280-400 mT) and low temperatures (2-70 K). The NV centers in synthetic
type IIb diamonds (nitrogen impurity concentration ~ppm) are prepared with
bulk concentrations of cm to cm
by high-energy electron irradiation and subsequent annealing. We find that a
proper post-radiation anneal (1000C for 60 mins) is critically
important to repair the radiation damage and to recover long electron spin
coherence times for NVs. After the annealing, spin coherence times of T~ms at 5~K are achieved, being only limited by C nuclear spectral
diffusion in natural abundance diamonds. At X-band magnetic fields, strong
electron spin echo envelope modulation (ESEEM) is observed originating from the
central N nucleus. The ESEEM spectral analysis allows for accurate
determination of the N nuclear hypefine and quadrupole tensors. In
addition, the ESEEM effects from two proximal C sites (second-nearest
neighbor and fourth-nearest neighbor) are resolved and the respective C
hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure
Generalized Drude model: Unification of ballistic and diffusive electron transport
For electron transport in parallel-plane semiconducting structures, a model
is developed that unifies ballistic and diffusive transport and thus
generalizes the Drude model. The unified model is valid for arbitrary magnitude
of the mean free path and arbitrary shape of the conduction band edge profile.
Universal formulas are obtained for the current-voltage characteristic in the
nondegenerate case and for the zero-bias conductance in the degenerate case,
which describe in a transparent manner the interplay of ballistic and diffusive
transport. The semiclassical approach is adopted, but quantum corrections
allowing for tunneling are included. Examples are considered, in particular the
case of chains of grains in polycrystalline or microcrystalline semiconductors
with grain size comparable to, or smaller than, the mean free path. Substantial
deviations of the results of the unified model from those of the ballistic
thermionic-emission model and of the drift-diffusion model are found. The
formulation of the model is one-dimensional, but it is argued that its results
should not differ substantially from those of a fully three-dimensional
treatment.Comment: 14 pages, 5 figures, REVTEX file, to appear in J. Phys.: Condens.
Matte
Iron porphyrin molecules on Cu(001): Influence of adlayers and ligands on the magnetic properties
The structural and magnetic properties of Fe octaethylporphyrin (OEP)
molecules on Cu(001) have been investigated by means of density functional
theory (DFT) methods and X-ray absorption spectroscopy. The molecules have been
adsorbed on the bare metal surface and on an oxygen-covered surface, which
shows a reconstruction. In order to allow
for a direct comparison between magnetic moments obtained from sum-rule
analysis and DFT we calculate the dipolar term , which is also
important in view of the magnetic anisotropy of the molecule. The measured
X-ray magnetic circular dichroism shows a strong dependence on the photon
incidence angle, which we could relate to a huge value of , e.g. on
Cu(001) amounts to -2.07\,\mbo{} for normal incidence leading to a
reduction of the effective spin moment . Calculations have also
been performed to study the influence of possible ligands such as Cl and O
atoms on the magnetic properties of the molecule and the interaction between
molecule and surface, because the experimental spectra display a clear
dependence on the ligand, which is used to stabilize the molecule in the gas
phase. Both types of ligands weaken the hybridization between surface and
porphyrin molecule and change the magnetic spin state of the molecule, but the
changes in the X-ray absorption are clearly related to residual Cl ligands.Comment: 17 figures, full articl
Verarbeitung und Vermarktung von ökologischem Schweinefleisch in Baden-Württemberg
Die Zielsetzung dieser Arbeit ist, Qualitätsansprüche an ökologisch erzeugtes Schweinefleisch und dessen Verarbeitungsprodukte aufzuzeigen. Dabei sollen einerseits die Qualitätsansprüche und mögliche Probleme auf der Verbraucherebene erfasst und andererseits auf der Verarbeiterebene auftretende Probleme hinsichtlich des Bezugs, der Verarbeitung und Vermarktung von Ökoschweinefleisch und Ökoschweinefleischerzeugnissen aufgezeigt werden. Um Informationen zur Thematik zu erhalten, wurden Verbraucher und Verarbeiter unabhängig voneinander befragt. Die Befragungen der Verbraucher und Verarbeiter erfolgte im Großraum Stuttgart
Salmonella Degrades the Host Glycocalyx Leading to Altered Infection and Glycan Remodeling.
Complex glycans cover the gut epithelial surface to protect the cell from the environment. Invasive pathogens must breach the glycan layer before initiating infection. While glycan degradation is crucial for infection, this process is inadequately understood. Salmonella contains 47 glycosyl hydrolases (GHs) that may degrade the glycan. We hypothesized that keystone genes from the entire GH complement of Salmonella are required to degrade glycans to change infection. This study determined that GHs recognize the terminal monosaccharides (N-acetylneuraminic acid (Neu5Ac), galactose, mannose, and fucose) and significantly (p < 0.05) alter infection. During infection, Salmonella used its two GHs sialidase nanH and amylase malS for internalization by targeting different glycan structures. The host glycans were altered during Salmonella association via the induction of N-glycan biosynthesis pathways leading to modification of host glycans by increasing fucosylation and mannose content, while decreasing sialylation. Gene expression analysis indicated that the host cell responded by regulating more than 50 genes resulting in remodeled glycans in response to Salmonella treatment. This study established the glycan structures on colonic epithelial cells, determined that Salmonella required two keystone GHs for internalization, and left remodeled host glycans as a result of infection. These data indicate that microbial GHs are undiscovered virulence factors
Large-Scale Release of Campylobacter Draft Genomes: Resources for Food Safety and Public Health from the 100K Pathogen Genome Project.
Campylobacter is a food-associated bacterium and a leading cause of foodborne illness worldwide, being associated with poultry in the food supply. This is the initial public release of 202 Campylobacter genome sequences as part of the 100K Pathogen Genome Project. These isolates represent global genomic diversity in the Campylobacter genus
Reaching the quantum limit of sensitivity in electron spin resonance
We report pulsed electron-spin resonance (ESR) measurements on an ensemble of
Bismuth donors in Silicon cooled at 10mK in a dilution refrigerator. Using a
Josephson parametric microwave amplifier combined with high-quality factor
superconducting micro-resonators cooled at millikelvin temperatures, we improve
the state-of-the-art sensitivity of inductive ESR detection by nearly 4 orders
of magnitude. We demonstrate the detection of 1700 bismuth donor spins in
silicon within a single Hahn echo with unit signal-to-noise (SNR) ratio,
reduced to just 150 spins by averaging a single Carr-Purcell-Meiboom-Gill
sequence. This unprecedented sensitivity reaches the limit set by quantum
fluctuations of the electromagnetic field instead of thermal or technical
noise, which constitutes a novel regime for magnetic resonance.Comment: Main text : 10 pages, 4 figures. Supplementary text : 16 pages, 8
figure
Recommended from our members
Draft Genome Sequences of 1,183 Salmonella Strains from the 100K Pathogen Genome Project.
Salmonella is a common food-associated bacterium that has substantial impact on worldwide human health and the global economy. This is the public release of 1,183 Salmonella draft genome sequences as part of the 100K Pathogen Genome Project. These isolates represent global genomic diversity in the Salmonella genus
The brain’s conversation with itself: neural substrates of dialogic inner speech
Inner speech has been implicated in important aspects of normal and atypical cognition, including the development of auditory hallucinations. Studies to date have focused on covert speech elicited by simple word or sentence repetition, while ignoring richer and arguably more psychologically significant varieties of inner speech. This study compared neural activation for inner speech involving conversations (‘dialogic inner speech’) with single-speaker scenarios (‘monologic inner speech’). Inner speech-related activation differences were then compared with activations relating to Theory-of-Mind (ToM) reasoning and visual perspective-taking in a conjunction design. Generation of dialogic (compared with monologic) scenarios was associated with a widespread bilateral network including left and right superior temporal gyri, precuneus, posterior cingulate and left inferior and medial frontal gyri. Activation associated with dialogic scenarios and ToM reasoning overlapped in areas of right posterior temporal cortex previously linked to mental state representation. Implications for understanding verbal cognition in typical and atypical populations are discussed
- …