1,781 research outputs found
New exact solution of the one dimensional Dirac Equation for the Woods-Saxon potential within the effective mass case
We study the one-dimensional Dirac equation in the framework of a position
dependent mass under the action of a Woods-Saxon external potential. We find
that constraining appropriately the mass function it is possible to obtain a
solution of the problem in terms of the hypergeometric function. The mass
function for which this turns out to be possible is continuous. In particular
we study the scattering problem and derive exact expressions for the reflection
and transmission coefficients which are compared to those of the constant mass
case. For the very same mass function the bound state problem is also solved,
providing a transcendental equation for the energy eigenvalues which is solved
numerically.Comment: Version to match the one which has been accepted for publication by
J. Phys. A: Math. Theor. Added one figure, several comments and few
references. (24 pages and 7 figures
SHIFTED 1/N EXPANSION FOR THE KLEIN-GORDON EQUATION WITH VECTOR AND SCALAR POTENTIALS
The shifted 1/N expansion method has been extended to solve the Klein-Gordon equation with both scalar and vector potentials. The calculations are carried out to the third-order correction in the energy series. The analytical results are applied to a linear scalar potential to obtain the relativistic energy eigenvalues. Our numerical results are compared with those obtained by Gunion and Li [Phys. Rev. D 12, 3583 (1975)]
"Double-trace" Deformations, Boundary Conditions and Spacetime Singularities
Double-trace deformations of the AdS/CFT duality result in a new perturbation
expansion for string theory, based on a non-local worldsheet. We discuss some
aspects of the deformation in the low energy gravity approximation, where it
appears as a change in the boundary condition of fields. We relate unique
features of the boundary of AdS to the worldsheet becoming non-local, and
conjecture that non-local worldsheet actions may be generic in other classes of
backgrounds.Comment: 21 pages, 2 figures, harvmac. v2: minor changes, references added,
version sent to JHEP. v3 minor correction
Tenascin-C Mimetic Peptide Nanofibers Direct Stem Cell Differentiation to Osteogenic Lineage
Cataloged from PDF version of article.Extracellular matrix contains various signals for cell surface receptors that regulate cell fate through modulation of cellular activities such as proliferation and differentiation. Cues from extracellular matrix components can be used for development of new materials to control the stem cell fate. In this study, we achieved control of stem cell fate toward osteogenic commitment by using a single extracellular matrix element despite the contradictory effect of mechanical stiffness. For this purpose, we mimicked bone extracellular matrix by incorporating functional sequence of fibronectin type III domain from native tenascin-C on self-assembled peptide nanofibers. When rat mesenchymal stem cells (rMSCs) were cultured on these peptide nanofibers, alkaline phosphatase (ALP) activity and alizarin red staining indicated osteogenic differentiation even in the absence of osteogenic supplements. Moreover, expression levels of osteogenic marker genes were significantly enhanced revealed by quantitative real-time polymerase chain reaction (qRT-PCR), which showed the remarkable bioactive role of this nanofiber system on osteogenic differentiation. Overall, these results showed that tenascin-C mimetic peptides significantly enhanced the attachment, proliferation, and osteogenic differentiation of rMSCs even in the absence of any external bioactive factors and regardless of the suitable stiff mechanical properties normally required for osteogenic differentiation. Thus, these peptide nanofibers provide a promising new platform for bone regeneratio
Scattering states of a particle, with position-dependent mass, in a symmetric heterojunction
The study of a particle with position-dependent effective mass (pdem), within
a double heterojunction is extended into the complex domain --- when the region
within the heterojunctions is described by a non Hermitian
symmetric potential. After obtaining the exact analytical solutions, the
reflection and transmission coefficients are calculated, and plotted as a
function of the energy. It is observed that at least two of the characteristic
features of non Hermitian symmetric systems --- viz., left / right
asymmetry and anomalous behaviour at spectral singularity, are preserved even
in the presence of pdem. The possibility of charge conservation is also
discussed.Comment: 12 pages, including 6 figures; Journal of Physics A : Math. Theor.
(2012
Temporal evolution of carbon stocks, fluxes and carbon balance in pedunculate oak chronosequence under close-to-nature forest management
Under current environmental changes, forest management is challenged to foster contrasting benefits from forests, such as continuous wood supply while preserving biomass production, biodiversity conservation, and contribution to climate change mitigation through atmospheric carbon sequestration. Although being found as globally important, estimates of long-term forest C balance are still highly uncertain. In this context, the chronosequence experiments (space-for-time substitution) might fill this gap in even-aged forests, as they represent an approach that enables the assessment of forest net C balance in the long term. In this research, we explored the dynamics of C stocks and fluxes in different forest pools throughout the rotation period (140 years) of a Pedunculate oak (Quercus robur L.) forest in Croatia. For this purpose, we selected a chronosequence that was made up of seven forest stands with different age (5, 13, 38, 53, 68, 108, and 138 years). To address the issues of uncertainty in C balance estimates, we compared net ecosystem carbon balance (NECB) estimated while using two different approaches, which we name pool-change (from C stocks) approach and component-flux (from C fluxes) approach. Overall, the pool-change approach showed higher NECB estimate, with the greatest difference being observed in younger stands (<50 years). Component-flux approach showed significantly higher uncertainty. Throughout the rotation period, managed pedunculate oak stands become a C sink early in their development phase, between the age of 13 and 35 years according to pool-change and component-flux approach, respectively. During the 140 years, oak forest provided 187.2 Mg C ha−1 (604 m3 ha−1) through thinnings and 147.9 Mg C ha−1 (477 m3 ha−1) in the final cut, while preserving, on average, 88.9 Mg C ha−1 in mineral soil down to 40 cm, 18.2 Mg C ha−1 in dead wood, and 6.0 Mg C ha−1 in the forest floor. Soil C stocks in our chronosequence did not show any age-related trend, indicating that current management practice has no negative effect on soil C stocks. Finally, under current close-to-nature forest management, Pedunculate oak forest showed to be sustainable in providing both economic and ecological ecosystem services
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