855 research outputs found
On the dynamics of vortex modes within magnetic islands
Recent work investigating the interaction of magnetic islands with
micro-turbulence has uncovered the striking observation of large scale vortex
modes forming within the island structure [W.A. Hornsby {\it et al.}, Phys.
Plasmas {\bf 17} 092301 (2010)]. These electrostatic vortices are found to be
the size of the island and are oscillatory. It is this oscillatory behaviour
and the presence of turbulence that leads us to believe that the dynamics are
related to the Geodesic Acoustic Mode (GAM), and it is this link that is
investigated in this paper.
Here we derive an equation for the GAM in the MHD limit, in the presence of a
magnetic island modified three-dimensional axisymmetric geometry. The
eigenvalues and eigenfunctions are calculated numerically and then utilised to
analyse the dynamics of oscillatory large-scale electrostatic potential
structures seen in both linear and non-linear gyro-kinetic simulations
Heterogeneity of Human Gingival Fibroblasts in Tobaccostimulated Collagen Degradation
poster abstractMatrix metalloproteinases (MMPs) are a large family of zinc-dependent endopeptidases and their activity is modulated by tissue inhibitors of metalloproteinases (TIMPs). Smoking is a risk factor for periodontal disease. Cigarette smoke condensate (CSC) is the particulate matter of cigarette smoke. Human gingival fibroblasts (HGFs) are one of major cellular components in periodontal tissue. CSC can increase collagen degradation of HGFs by enhancing and altering the localization of MMPs. Previous clinical studies also showed that some smoking people even with very high dental plaque index still had good periodontal status and did not develop periodontal disease. Objectives: The aim of this study was to investigate the heterogeneity of HGFs to CSC-stimulated collagen degradation and to start examining its mechanisms. Methods: Eleven HGF cell lines were established from healthy gingival tissue from patients undergoing crown-lengthening surgery. HGFs were seeded as single colony (75,000 cells/well) in 6-well Type I collagen coated plates and exposed to 100 µg/ml CSC (Murty Pharmaceuticals,
Lexington, KY) diluted in serum-free media with/without a MMPs inhibitor (GM6001, 100 nM, Chemicon, Temecla, CA) for 3 days. HGFs were seeded with serum free media alone as controls. The mRNA levels of multiple MMPs/TIMPs were measured by reverse transcriptionpolymerase chain reaction. Results: CSC increased collagen degradation in 7 HGF cell lines (CSC-susceptible HGFs), but not in 4 HGF cell lines (CSC-unsusceptible HGFs). GM6001 inhibited CSC-stimulated collagen degradation in all of CSC-susceptible HGFs. The mRNA levels of MMP-1, MMP-2, MMP-3, MMP-14, TIMP-1, and TIMP-2 increased 2.5, 1.3, 3.9, 2.0, 1.6, and 1.3 fold, respectively, in the CSC-susceptible HGFs. However, expression of MMPs/TIMPs basically didn’t change in the CSC-unsusceptible HGFs, except for MMP-3 which increased 1.4 fold. Conclusions: Heterogeneity of HGFs existed in regard to the CSC-stimulated collagen degradation and the altered expression of the MMPs/TIMPs may be responsible for this heterogeneity. This project was supported by the IUPUI Tobacco Cessation and Biobehavioral Center
Picosecond detection of an intermediate in the photochemical reaction of bacterial photosynthesis.
Crystal Symmetry Lowering in Chiral Multiferroic BaTaFeSiO observed by X-Ray Magnetic Scattering
Chiral multiferroic langasites have attracted attention due to their
doubly-chiral magnetic ground state within an enantiomorphic crystal. We report
on a detailed resonant soft X-ray diffraction study of the multiferroic
BaTaFeSiO at the Fe and oxygen edges. Below
() we observe the satellite reflections ,
, and where . The dependence of the scattering intensity on X-ray polarization and
azimuthal angle indicate that the odd harmonics are dominated by the
out-of-plane (-axis) magnetic dipole while the
originates from the electron density distortions accompanying magnetic order.
We observe dissimilar energy dependences of the diffraction intensity of the
purely magnetic odd-harmonic satellites at the Fe edge. Utilizing
first-principles calculations, we show that this is a consequence of the loss
of threefold crystal symmetry in the multiferroic phase
Multiple magnetic ordering phenomena in multiferroic o-HoMnO3
Orthorhombic HoMnO3 is a multiferroic in which Mn antiferromagnetic order
induces ferroelectricity. A second transition occurs within the multiferroic
phase, in which a strong enhancement of the ferroelectric polarization occurs
concomitantly to antiferromagnetic ordering of Ho 4f magnetic moments. Using
the element selectivity of resonant X-ray diffraction, we study the magnetic
order of the Mn 3d and Ho 4f moments. We explicitly show that the Mn magnetic
order is affected by the Ho 4f magnetic ordering transition. Based on the
azimuthal dependence of the (0 q 0) and (0 1-q 0) magnetic reflections, we
suggest that the Ho 4f order is similar to that previously observed for Tb 4f
in TbMnO3, which resembles an ac-cycloid. This is unlike the Mn order, which
has already been shown to be different for the two materials. Using
non-resonant diffraction, we show that the magnetically-induced ferroelectric
lattice distortion is unaffected by the Ho ordering, suggesting a mechanism
through which the Ho order affects polarization without affecting the lattice
in the same manner as the Mn order
Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3
We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray
diffraction probe measurements to investigate the coupling between the
photoexcited electronic system and the spin cycloid magnetic order in
multiferroic TbMnO3 at low temperatures. We observe melting of the long range
antiferromagnetic order at low excitation fluences with a decay time constant
of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously
observed in other systems. To explain the data we propose a simple model of the
melting process where the pump laser pulse directly excites the electronic
system, which then leads to an increase in the effective temperature of the
spin system via a slower relaxation mechanism. Despite this apparent increase
in the effective spin temperature, we do not observe changes in the wavevector
q of the antiferromagnetic spin order that would typically correlate with an
increase in temperature under equilibrium conditions. We suggest that this
behavior results from the extremely low magnon group velocity that hinders a
change in the spin-spiral wavevector on these time scales.Comment: 9 pages, 4 figure
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