1,558 research outputs found
Local Nature of Coset Models
The local algebras of the maximal Coset model C_max associated with a chiral
conformal subtheory A\subset B are shown to coincide with the local relative
commutants of A in B, provided A contains a stress energy tensor.
Making the same assumption, the adjoint action of the unique
inner-implementing representation U^A associated with A\subset B on the local
observables in B is found to define net-endomorphisms of B. This property is
exploited for constructing from B a conformally covariant holographic image in
1+1 dimensions which proves useful as a geometric picture for the joint
inclusion A\vee C_max \subset B.
Immediate applications to the analysis of current subalgebras are given and
the relation to normal canonical tensor product subfactors is clarified. A
natural converse of Borchers' theorem on half-sided translations is made
accessible.Comment: 33 pages, no figures; typos, minor improvement
Structure of self-assembled Mn atom chains on Si(001)
Mn has been found to self-assemble into atomic chains running perpendicular
to the surface dimer reconstruction on Si(001). They differ from other atomic
chains by a striking asymmetric appearance in filled state scanning tunneling
microscopy (STM) images. This has prompted complicated structural models
involving up to three Mn atoms per chain unit. Combining STM, atomic force
microscopy and density functional theory we find that a simple necklace-like
chain of single Mn atoms reproduces all their prominent features, including
their asymmetry not captured by current models. The upshot is a remarkably
simpler structure for modelling the electronic and magnetic properties of Mn
atom chains on Si(001).Comment: 5 pages, 4 figure
Myosin II filament dynamics in actin networks revealed with interferometric scattering microscopy
The plasma membrane and the underlying cytoskeletal cortex constitute active platforms for a variety of cellular processes. Recent work has shown that the remodeling acto-myosin network modifies local membrane organization, but the molecular details are only partly understood due to difficulties with experimentally accessing the relevant time and length scales. Here, we use interferometric scattering (iSCAT) microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer membrane. Using the magnitude of the interferometric contrast, which is proportional to molecular mass, and fast acquisition rates, we detect, and image individual membrane attached actin filaments diffusing within the acto-myosin network and follow individual myosin II filament dynamics. We quantify myosin II filament dwell times and processivity as functions of ATP concentration, providing experimental evidence for the predicted ensemble behavior of myosin head domains. Our results show how decreasing ATP concentrations lead to both increasing dwell times of individual myosin II filaments and a global change from a remodeling to a contractile state of the acto-myosin network
Endotaxial Si nanolines in Si(001):H
We present a detailed study of the structural and electronic properties of a
self-assembled silicon nanoline embedded in the H-terminated silicon (001)
surface, known as the Haiku stripe. The nanoline is a perfectly straight and
defect free endotaxial structure of huge aspect ratio; it can grow micrometre
long at a constant width of exactly four Si dimers (1.54nm). Another remarkable
property is its capacity to be exposed to air without suffering any
degradation. The nanoline grows independently of any step edges at tunable
densities, from isolated nanolines to a dense array of nanolines. In addition
to these unique structural characteristics, scanning tunnelling microscopy and
density functional theory reveal a one-dimensional state confined along the
Haiku core. This nanoline is a promising candidate for the long sought after
electronic solid-state one-dimensional model system to explore the fascinating
quantum properties emerging in such reduced dimensionality.Comment: 8 pages, 6 figure
One dimensional Si-in-Si(001) template for single-atom wire growth
Single atom metallic wires of arbitrary length are of immense technological
and scientific interest. We describe a novel silicon-only template enabling the
self-organised growth of isolated micrometer long surface and subsurface
single-atom chains. It consists of a one dimensional, defect-free
reconstruction - the Haiku core, here revealed for the first time in details -
self-assembled on hydrogenated Si(001) terraces, independent of any step edges.
We discuss the potential of this Si-in-Si template as an appealing alternative
to vicinal surfaces for nanoscale patterning.Comment: 3 pages, 2 figure
Effect of the Salmonella Pathogenicity Island 2 Type III Secretion System on Salmonella Survival in Activated Chicken Macrophage-Like HD11 Cells
In order to better identify the role of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (T3SS) in chickens, we used the well-known gentamicin protection assay with activated HD11 cells. HD11 cells are a macrophage-like chicken cell line that can be stimulated with phorbol 12-myristate 13-acetate (PMA) to exhibit more macrophage-like morphology and greater production of reactive oxygen species (ROS). Activated HD11 cells were infected with a wild-type Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) strain, a SPI-2 mutant S. Typhimurium strain, a wild-type Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) strain, a SPI-2 mutant S. Enteritidis strain, or a non-pathogenic Escherichia coli (E. coli) strain. SPI-2 mutant strains were found to survive as well as their parent strain at all time points post-uptake (PU) by the HD11 cells, up to 24 h PU, while the E. coli strain was no longer recoverable by 3 h PU. We can conclude from these observations that the SPI-2 T3SS of S. Typhimurium and S. Enteritidis is not important for survival of Salmonella in the activated macrophage-like HD11 cell line, and that Salmonella must employ other mechanisms for survival in this environment, as E. coli is effectively eliminated
Structural changes of Pd-13 upon charging and oxidation/reduction
First-principle generalized gradient corrected density functional calculations have been performed to study the stability of cationic and anionic Pd13 +/−, and neutral Pd13O2 clusters. It is found that while cationic Pd13 + favors a C s geometry similar to the neutral Pd13, both anionic Pd13 − and neutral Pd13O2 favor a compact ∼I h structure. A detailed analysis of the electronic structure shows that the stabilization of the delocalized 1P and 2P cluster orbitals, and the hybridization of the 1D orbitals with the oxygen atomic p orbitals play an important role in the energetic ordering of C s and ∼I h isomers. A structural oscillation is predicted during an oxidation/reduction cycle of Pd13 in which small energy barriers between 0.3 and 0.4 eV are involved
Measurement of the -asymmetry parameter of Cu in search for tensor type currents in the weak interaction
Precision measurements at low energy search for physics beyond the Standard
Model in a way complementary to searches for new particles at colliders. In the
weak sector the most general decay Hamiltonian contains, besides vector
and axial-vector terms, also scalar, tensor and pseudoscalar terms. Current
limits on the scalar and tensor coupling constants from neutron and nuclear
decay are on the level of several percent.
The goal of this paper is extracting new information on tensor coupling
constants by measuring the -asymmetry parameter in the pure Gamow-Teller
decay of Cu, thereby testing the V-A structure of the weak interaction.
An iron sample foil into which the radioactive nuclei were implanted was cooled
down to milliKelvin temperatures in a He-He dilution refrigerator. An
external magnetic field of 0.1 T, in combination with the internal hyperfine
magnetic field, oriented the nuclei. The anisotropic radiation was
observed with planar high purity germanium detectors operating at a temperature
of about 10\,K. An on-line measurement of the asymmetry of Cu
was performed as well for normalization purposes. Systematic effects were
investigated using Geant4 simulations.
The experimental value, = 0.587(14), is in agreement with the
Standard Model value of 0.5991(2) and is interpreted in terms of physics beyond
the Standard Model. The limits obtained on possible tensor type charged
currents in the weak interaction hamiltonian are -0.045
0.159 (90\% C.L.). The obtained limits are comparable to limits from other
correlation measurements in nuclear decay and contribute to further
constraining tensor coupling constants
Directed Rh(I)-Catalyzed Asymmetric Hydroboration of Prochiral 1-Arylcycloprop-2-ene-1-carboxylic Acid Derivatives
This is the peer reviewed version of the following article: A. Edwards, M. Rubina, M. Rubin, Chem. Eur. J. 2018, 24, 1394., which has been published in final form at http://doi.org/10.1002/chem.201704443. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.A full account on rhodium-catalyzed asymmetric, directed hydroboration of functionalized prochiral cyclopropenes affording enantiomerically enriched cyclopropylboronates is reported. The scope and limitations of two alternate directing groups, ester and carboxamide, are evaluated. It was found that hydroboration of esters appeared to be more sensitive to substitution in the aromatic ring of the substrates. Specifically, ortho-halogens were detrimental for diastereo- and enantioselectivity, possibly because of additional coordination with rhodium. In contrast, more Lewis-basic amide directing groups allowed for stronger chelation to the transition metal, leading to consistently high diastereo- and enantioselectivity in hydroboration across a broader range of substrates
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