9,242 research outputs found
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
Integrin α2β1 Expression Regulates Matrix Metalloproteinase-1-Dependent Bronchial Epithelial Repair in Pulmonary Tuberculosis.
Pulmonary tuberculosis (TB) is caused by inhalation of Mycobacterium tuberculosis, which damages the bronchial epithelial barrier to establish local infection. Matrix metalloproteinase-1 plays a crucial role in the immunopathology of TB, causing breakdown of type I collagen and cavitation, but this collagenase is also potentially involved in bronchial epithelial repair. We hypothesized that the extracellular matrix (ECM) modulates M. tuberculosis-driven matrix metalloproteinase-1 expression by human bronchial epithelial cells (HBECs), regulating respiratory epithelial cell migration and repair. Medium from monocytes stimulated with M. tuberculosis induced collagenase activity in bronchial epithelial cells, which was reduced by ~87% when cells were cultured on a type I collagen matrix. Matrix metalloproteinase-1 had a focal localization, which is consistent with cell migration, and overall secretion decreased by 32% on type I collagen. There were no associated changes in the specific tissue inhibitors of metalloproteinases. Decreased matrix metalloproteinase-1 secretion was due to ligand-binding to the α2β1 integrin and was dependent on the actin cytoskeleton. In lung biopsies, samples from patients with pulmonary TB, integrin α2β1 is highly expressed on the bronchial epithelium. Areas of lung with disrupted collagen matrix showed an increase in matrix metalloproteinases-1 expression compared with areas where collagen was comparable to control lung. Type I collagen matrix increased respiratory epithelial cell migration in a wound-healing assay, and this too was matrix metalloproteinase-dependent, since it was blocked by the matrix metalloproteinase inhibitor GM6001. In summary, we report a novel mechanism by which α2β1-mediated signals from the ECM modulate matrix metalloproteinase-1 secretion by HBECs, regulating their migration and epithelial repair in TB
Optical transitions in highly-charged californium ions with high sensitivity to variation of the fine-structure constant
We study electronic transitions in highly-charged Cf ions that are within the
frequency range of optical lasers and have very high sensitivity to potential
variations in the fine-structure constant, alpha. The transitions are in the
optical despite the large ionisation energies because they lie on the
level-crossing of the 5f and 6p valence orbitals in the thallium isoelectronic
sequence. Cf16+ is a particularly rich ion, having several narrow lines with
properties that minimize certain systematic effects. Cf16+ has very large
nuclear charge and large ionisation energy, resulting in the largest
alpha-sensitivity seen in atomic systems. The lines include positive and
negative shifters
Heat capacity anomaly at the quantum critical point of the Transverse Ising Magnet CoNb_2O_6
The transverse Ising magnet Hamiltonian describing the Ising chain in a
transverse magnetic field is the archetypal example of a system that undergoes
a transition at a quantum critical point (QCP). The columbite CoNbO is
the closest realization of the transverse Ising magnet found to date. At low
temperatures, neutron diffraction has observed a set of discrete collective
spin modes near the QCP. We ask if there are low-lying spin excitations
distinct from these relatively high energy modes. Using the heat capacity, we
show that a significant band of gapless spin excitations exists. At the QCP,
their spin entropy rises to a prominent peak that accounts for 30 of the
total spin degrees of freedom. In a narrow field interval below the QCP, the
gapless excitations display a fermion-like, temperature-linear heat capacity
below 1 K. These novel gapless modes are the main spin excitations
participating in, and affected, by the quantum transition.Comment: 14 pages total, 8 figure
Empires and Percolation: Stochastic Merging of Adjacent Regions
We introduce a stochastic model in which adjacent planar regions merge
stochastically at some rate , and observe analogies with the
well-studied topics of mean-field coagulation and of bond percolation. Do
infinite regions appear in finite time? We give a simple condition on
for this {\em hegemony} property to hold, and another simple condition for it
to not hold, but there is a large gap between these conditions, which includes
the case . For this case, a non-rigorous analytic
argument and simulations suggest hegemony.Comment: 13 page
Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)
The phase diagram of non-hydrated Na(x)CoO(2) has been determined by changing
the Na content x using a series of chemical reactions. As x increases from 0.3,
the ground state goes from a paramagnetic metal to a charge-ordered insulator
(at x=1/2) to a `Curie-Weiss metal' (around 0.70), and finally to a weak-moment
magnetically ordered state (x>0.75). The unusual properties of the state at 1/2
(including particle-hole symmetry at low T and enhanced thermal conductivity)
are described. The strong coupling between the Na ions and the holes is
emphasized.Comment: 4 pages with 3 figures, changed conten
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