270 research outputs found
Computational modeling of sublattice magnetizations of nano-magnetic layered materials
In the present work, we model the salient magnetic properties of the alloy
layered ferrimagnetic nanostructures
between
magnetically ordered cobalt leads. The effective field theory (EFT) Ising spin
method is used to compute reliable and exchange values
for the pure cobalt and gadolinium materials in comparison with experimental
data. Using the combined EFT and mean field theory (MFT) spin methods, the
sublattice magnetizations of the and sites on the individual hcp
basal planes of the layered nanostructures, are calculated and analyzed. The
sublattice magnetizations, effective magnetic moments per site, and
compensation characteristics on the individual hcp atomic planes of the
embedded nanostructures are presented as a function of temperature and the
thicknesses of the layered ferrimagnetic nanostructures, for different stable
eutectic concentrations 0.5. In the absence of first principles
calculations for these basic physical variables for the layered nanostructures
between cobalt leads, the combined EFT and MFT approach, and appropriate
magnetic modeling of the well-defined interfaces of these systems, yield the
only available information for them at present. These magnetic variables are
necessary for spin dynamic computations, and for the ballistic magnon transport
across embedded nanojunctions in magnonics. The model is general, and may
applied directly to other composite magnetic elements and embedded
nanostructures
Nonbreaking wave‐induced mixing in upper ocean during tropical cyclones using coupled hurricane‐ocean‐wave modeling
The effects of turbulence generated by nonbreaking waves have been investigated by testing and evaluating a new nonbreaking wave parameterization in a coupled hurricane‐ocean‐wave model. The MPI version of the Princeton Ocean Model (POM) with hurricane forcing is coupled with the WAVEWATCH‐III (WW3) surface wave model. Hurricane Ivan is chosen as the test case due to its extreme intensity and availability of field data during its passage. The model results are validated against field observations of wave heights and sea surface temperatures (SSTs) from the National Data Buoy Centre (NDBC) during Hurricane Ivan and against limited in situ current and bottom temperature data. A series of numerical experiments is set up to examine the influence of the nonbreaking wave parameterization on the mixing of upper ocean. The SST response from the modeling experiments indicates that the nonbreaking wave‐induced mixing leads to significant cooling of the SST and deepening of the mixed layer. It was found that the nondimensional constant b1 in the nonbreaking wave parameterization has different impacts on the weak and the strong sides of the storm track. A constant value of b1 leads to improved predictions on the strong side of the storm while a steepness‐dependent b1 provides a better agreement with in situ observations on the weak side. A separate simulation of the intense tropical cyclone Olwyn in north‐west Australia revealed the same trend for b1 on the strong side of the tropical cyclone
Calcineurin/NFAT Activation-Dependence of Leptin Synthesis and Vascular Growth in Response to Mechanical Stretch
Background and Aims- Hypertension and obesity are important risk factors of cardiovascular disease. They are both associated with high leptin levels and have been shown to promote vascular hypertrophy, through the RhoA/ROCK and ERK1/2 phosphorylation. Calcineurin/NFAT activation also induces vascular hypertrophy by upregulating various genes. This study aimed to decipher whether a crosstalk exists between the RhoA/ROCK pathway, Ca+2/calcineurin/NFAT pathway, and ERK1/2 phosphorylation in the process of mechanical stretch-induced vascular smooth muscle cell (VSMC) hypertrophy and leptin synthesis. Methods and Results- Rat portal vein (RPV) organ culture was used to investigate the effect of mechanical stretch and exogenous leptin (3.1 nM) on VSMC hypertrophy and leptin synthesis. Results showed that stretching the RPV significantly upregulated leptin secretion, mRNA and protein expression, which were inhibited by the calcium channel blocker nifedipine (10 μM), the selective calcineurin inhibitor FK506 (1 nM) and the ERK1/2 inhibitor PD98059 (1 μM). The transcription inhibitor actinomycin D (0.1M) and the translation inhibitor cycloheximide (1 mM) significantly decreased stretch-induced leptin protein expression. Mechanical stretch or leptin caused an increase in wet weight changes and protein synthesis, considered as hypertrophic markers, while they were inhibited by FK506 (0.1 nM; 1 nM). In addition, stretch or exogenous leptin significantly increased calcineurin activity and MCIP1 expression whereas leptin induced NFAT nuclear translocation in VSMCs. Moreover, in response to stretch or exogenous leptin, the Rho inhibitor C3 exoenzyme (30 ng/mL), the ROCK inhibitor Y-27632 (10 μM), and the actin depolymerization agents Latrunculin B (50 nM) and cytochalasin D (1 μM) reduced calcineurin activation and NFAT nuclear translocation. ERK1/2 phosphorylation was inhibited by FK506 and C3. Conclusions- Mechanical stretch-induced VSMC hypertrophy and leptin synthesis and secretion is mediated by Ca2+/calcineurin/NFAT activation. RhoA/ROCK and ERK1/2 activation are critical for mechanical stretch-induced calcineurin activation
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