1,146 research outputs found
Diffusion-controlled phase growth on dislocations
We treat the problem of diffusion of solute atoms around screw dislocations.
In particular, we express and solve the diffusion equation, in radial symmetry,
in an elastic field of a screw dislocation subject to the flux conservation
boundary condition at the interface of a new phase. We consider an incoherent
second-phase precipitate growing under the action of the stress field of a
screw dislocation. The second-phase growth rate as a function of the
supersaturation and a strain energy parameter is evaluated in spatial
dimensions d=2 and d=3. Our calculations show that an increase in the amplitude
of dislocation force, e.g. the magnitude of the Burgers vector, enhances the
second-phase growth in an alloy. Moreover, a relationship linking the
supersaturation to the precipitate size in the presence of the elastic field of
dislocation is calculated.Comment: 10 pages, 4 figures, a revised version of the paper presented in
MS&T'08, October 5-9, 2008, Pittsburg
Power Spectrum in Krein Space Quantization
The power spectrum of scalar field and space-time metric perturbations
produced in the process of inflation of universe, have been presented in this
paper by an alternative approach to field quantization namely, Krein space
quantization [1,2]. Auxiliary negative norm states, the modes of which do not
interact with the physical world, have been utilized in this method. Presence
of negative norm states play the role of an automatic renormalization device
for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy
Clusters of Galaxies: New Results from the CLEF Hydrodynamics Simulation
Preliminary results are presented from the CLEF hydrodynamics simulation, a
large (N=2(428)^3 particles within a 200 Mpc/h comoving box) simulation of the
LCDM cosmology that includes both radiative cooling and a simple model for
galactic feedback. Specifically, we focus on the X-ray properties of the
simulated clusters at z=0 and demonstrate a reasonable level of agreement
between simulated and observed cluster scaling relations.Comment: 7 pages, 4 figures, accepted for publication in Advances in Space
Research (proceedings of the COSPAR 2004 Assembly, Paris
Comment on "Quantum diffusion of 3-He impurities in solid 4- He"
In this comment I show that the experimental data on quantum diffusion of
3-He impurities in solid 4-He can be explained using the adopted quasiparticle
theory. The contention by E.G. Kisvarsanyi and N.S. Sullivan (KS) in Phys.Rev.B
v. 48, 16557 (1993) as well as in their Reply (ibid. v. 55, 3989 (1997)) to the
Grigor'ev's Comment (Phys.Rev. B v. 55, 3987 (1997)) that "Pushkarov's theory
of phonon scattering fails to fit the data by very large factors" is groundless
and may result from their bad arithmetical error. This means that the
phonon-impurity scattering mechanism of diffusion is consistent with experiment
and its neglecting by KS makes their results questionable.Comment: RevTex, 5 pages, no figures, to be published in Phys.Rev.
Inhibition of osteocyte apoptosis prevents the increase in osteocytic receptor activator of nuclear factor κB ligand (RANKL) but does not stop bone resorption or the loss of bone induced by unloading
"This research was originally published in Journal of Biological Chemistry. Lilian I. Plotkin, Arancha R. Gortazar, Hannah M. Davis, Keith W. Condon, Hugo Gabilondo, Marta Maycas, Matthew R. Allen, and Teresita Bellido. Inhibition of Osteocyte Apoptosis Prevents the Increase in Osteocytic Receptor Activator of Nuclear Factor κB Ligand (RANKL) but Does Not Stop Bone Resorption or the Loss of Bone Induced by Unloading*. Journal of Biological Chemistry. 2015; 290:18934-18942. © the American Society for Biochemistry and Molecular Biology."Apoptosis of osteocytes and osteoblasts precedes bone resorption and bone loss with reduced mechanical stimulation, and receptor activator of NF-κB ligand (RANKL) expression is increased with unloading in mice. Because osteocytes are major RANKL producers, we hypothesized that apoptotic osteocytes signal to neighboring osteocytes to increase RANKL expression, which, in turn, increases osteoclastogenesis and bone resorption. The traditional bisphosphonate (BP) alendronate (Aln) or IG9402, a BP analog that does not inhibit resorption, prevented the increase in osteocyte apoptosis and osteocytic RANKL expression. The BPs also inhibited osteoblast apoptosis but did not prevent the increase in osteoblastic RANKL. Unloaded mice exhibited high serum levels of the bone resorption marker C-telopeptide fragments of type I collagen (CTX), elevated osteoclastogenesis, and increased osteoclasts in bone. Aln, but not IG9402, prevented all of these effects. In addition, Aln prevented the reduction in spinal and femoral bone mineral density, spinal bone volume/tissue volume, trabecular thickness, mechanical strength, and material strength induced by unloading. Although IG9402 did not prevent the loss of bone mass, it partially prevented the loss of strength, suggesting a contribution of osteocyte viability to strength independent of bone mass. These results demonstrate that osteocyte apoptosis leads to increased osteocytic RANKL. However, blockade of these events is not sufficient to restrain osteoclast formation, inhibit resorption, or stop bone loss induced by skeletal unloadingThis work was supported, in whole or in part, by National Institutes of Health Grants R01DK076007 and ARRA supplement S10-RR023710 (to T. B.) and R01AR053643 (to L. I. P.). This work was also supported by Veterans Affairs Merit Award I01BX002104 (to T. B.) and an IUSM Biomedical Research grant (to L. I. P.) and by scholarships from the Conchita Rábago Foundation (to A. R. G. and M. M.), the European Molecular Biology Organization (to M. M.), and Universidad Autónoma de Madrid (to H. G
Nkx2.1-derived astrocytes and neurons together with Slit2 are indispensable for anterior commissure formation.
Guidepost cells present at and surrounding the midline provide guidance cues that orient the growing axons through commissures. Here we show that the transcription factor Nkx2.1 known to control the specification of GABAergic interneurons also regulates the differentiation of astroglia and polydendrocytes within the mouse anterior commissure (AC). Nkx2.1-positive glia were found to originate from three germinal regions of the ventral telencephalon. Nkx2.1-derived glia were observed in and around the AC region by E14.5. Thereafter, a selective cell ablation strategy showed a synergistic role of Nkx2.1-derived cells, both GABAergic interneurons and astroglia, towards the proper formation of the AC. Finally, our results reveal that the Nkx2.1-regulated cells mediate AC axon guidance through the expression of the repellent cue, Slit2. These results bring forth interesting insights about the spatial and temporal origin of midline telencephalic glia, and highlight the importance of neurons and astroglia towards the formation of midline commissures
Stable Heterogeneity for the Production of Diffusible Factors in Cell Populations
The production of diffusible molecules that promote survival and growth is common in bacterial and eukaryotic cell populations, and can be considered a form of cooperation between cells. While evolutionary game theory shows that producers and non-producers can coexist in well-mixed populations, there is no consensus on the possibility of a stable polymorphism in spatially structured populations where the effect of the diffusible molecule extends beyond one-step neighbours. I study the dynamics of biological public goods using an evolutionary game on a lattice, taking into account two assumptions that have not been considered simultaneously in existing models: that the benefit of the diffusible molecule is a non-linear function of its concentration, and that the molecule diffuses according to a decreasing gradient. Stable coexistence of producers and non-producers is observed when the benefit of the molecule is a sigmoid function of its concentration, while strictly diminishing returns lead to coexistence only for very specific parameters and linear benefits never lead to coexistence. The shape of the diffusion gradient is largely irrelevant and can be approximated by a step function. Since the effect of a biological molecule is generally a sigmoid function of its concentration (as described by the Hill equation), linear benefits or strictly diminishing returns are not an appropriate approximations for the study of biological public goods. A stable polymorphism of producers and non-producers is in line with the predictions of evolutionary game theory and likely to be common in cell populations
Parametric analysis of energy harvesting pavements operated by air convection
In this paper, an energy harvesting pavement prototype using air as the operating fluid is described and analysed. The prototype harvests the thermal energy available in the pavement through pipes embedded in its structure, where air flows thanks to natural convection. The air is able to exit the system through an updraft chimney. A parametric analysis of the controllable parameters of interest is performed in this work in order to evaluate the variation in the performance of the energy harvesting prototype in different experimental setups.
This study shows that there exists a maximum value for the air speed in each configuration and that the energy harvesting efficiency depends on the height and the diameter of the chimney. Moreover, there is a minimum value of the chimney diameter that does not allow air movement and makes the whole system behave as if no pipes were embedded in the pavement structure
Fast Diffusion Process in Quenched hcp Dilute Solid He-He Mixture
The study of phase structure of dilute He - He solid mixture of
different quality is performed by spin echo NMR technique. The diffusion
coefficient is determined for each coexistent phase. Two diffusion processes
are observed in rapidly quenched (non-equilibrium) hcp samples: the first
process has a diffusion coefficient corresponding to hcp phase, the second one
has huge diffusion coefficient corresponding to liquid phase. That is evidence
of liquid-like inclusions formation during fast crystal growing. It is
established that these inclusions disappear in equilibrium crystals after
careful annealing.Comment: 7 pages, 3 figures, QFS200
- …