24 research outputs found
Casimir-Polder interaction of fullerene molecules with surfaces
We calculate the thermal Casimir--Polder potential of C60 and C70 fullerene
molecules near gold and silicon nitride surfaces, motivated by their relevance
for molecular matter wave interference experiments. We obtain the coefficients
governing the asymptotic power laws of the interaction in the thermal, retarded
and nonretarded distance regimes and evaluate the full potential numerically.
The interaction is found to be dominated by electronic transitions, and hence
independent of the internal temperature of the molecules. The contributions
from phonon transitions, which are affected by the molecular temperature, give
rise to only a small correction. Moreover, we find that the sizeable molecular
line widths of thermal fullerenes may modify the nonretarded interaction,
depending on the model used. Detailed measurements of the nonretarded potential
of fullerene thus allow one to distinguish between different theories of
incorporating damping.Comment: 9 pages, 8 figures, 9 table
Thermal Casimir vs Casimir-Polder forces: Equilibrium and non-equilibrium forces
We critically discuss the common belief that the thermal Casimir-Polder force
can always be represented as a Matsubara sum, as it is true for the Casimir
force. On the contrary, an exact treatment of the atom-field coupling reveals
that for a ground-state atom, terms associated with virtual-photon absorption
contribute to the force which are identified as a signature of non-equilibrium
dynamics. Even the equilibrium force on a thermalized atom or molecule may be
overestimated when using the ground-state polarizability instead of its thermal
counterpart.Comment: 5 pages, 0 figures, minor addition
Local-field correction to one- and two-atom van der Waals interactions
Based on macroscopic quantum electrodynamics in linearly and causally
responding media, we study the local-field corrected van der Waals potentials
and forces for unpolarized ground-state atoms placed within a magnetoelectric
medium of arbitrary size and shape. We start from general expressions for the
van der Waals potentials in terms of the (classical) Green tensor of the
electromagnetic field and the atomic polarizability and incorporate the
local-field correction by means of the real-cavity model. In this context,
special emphasis is given to the decomposition of the Green tensor into a
medium part multiplied by a global local-field correction factor and, in the
single-atom case, a part that only depends on the cavity characteristics. The
result is used to derive general formulas for the local-field corrected van der
Waals potentials and forces. As an application, we calculate the van der Waals
potential between two ground-state atoms placed within magnetoelectric bulk
material.Comment: 9 pages, 2 figures, corrections according to erratu
Image method in the calculation of the van der Waals force between an atom and a conducting surface
Initially, we make a detailed historical survey of van der Waals forces,
collecting the main references on the subject. Then, we review a method
recently proposed by Eberlein and Zietal to compute the dispersion van der
Waals interaction between a neutral but polarizable atom and a perfectly
conducting surface of arbitrary shape. This method has the advantage of
relating the quantum problem to a corresponding classical one in electrostatics
so that all one needs is to compute an appropriate Green function. We show how
the image method of electrostatics can be conveniently used together with the
Eberlein and Zietal mehtod (when the problem admits an image solution). We then
illustrate this method in a couple of simple but important cases, including the
atom-sphere system. Particularly, in our last example, we present an original
result, namely, the van der Waals force between an atom and a boss hat made of
a grounded conducting material.Comment: This is a pedagogical and introductory paper on van der Waals forces
between an atom and a conducting surfac
Local-field corrected van der Waals potentials in magnetodielectric multilayer systems
Within the framework of macroscopic quantum electrodynamics in linear, causal
media, we study the van der Waals potentials of ground-state atoms in planar
magnetodielectric host media. Our investigation extends earlier ones in two
aspects: It allows for the atom to be embedded in a medium, thus covers many
more realistic systems; and it takes account of the local-field correction.
Two- and three-layer configurations are treated in detail both analytically and
numerically. It is shown that an interplay of electric and magnetic properties
in neighbouring media may give rise to potential wells or walls. Local-field
corrections as high as 80% are found. By calculating the full potential
including the translationally invariant and variant parts, we propose a way to
estimate the (finite) value of the dispersion potential at the surface between
two media. Connection with earlier work intended for biological applications is
established.Comment: 12 pages, 5 figure
Local erythropoietin and endothelial progenitor cells improve regional cardiac function in acute myocardial infarction
<p>Abstract</p> <p>Background</p> <p>Expanded endothelial progenitor cells (eEPC) improve global left ventricular function in experimental myocardial infarction (MI). Erythropoietin beta (EPO) applied together with eEPC may improve regional myocardial function even further by anti-apoptotic and cardioprotective effects. Aim of this study was to evaluate intramyocardial application of eEPCs and EPO as compared to eEPCs or EPO alone in experimental MI.</p> <p>Methods and Results</p> <p>In vitro experiments revealed that EPO dosed-dependently decreased eEPC and leukocyte apoptosis. Moreover, in the presence of EPO mRNA expression in eEPC of proangiogenic and proinflammatory mediators measured by TaqMan PCR was enhanced. Experimental MI was induced by ligation and reperfusion of the left anterior descending coronary artery of nude rats (n = 8-9). After myocardial transplantation of eEPC and EPO CD68+ leukocyte count and vessel density were enhanced in the border zone of the infarct area. Moreover, apoptosis of transplanted CD31 + TUNEL + eEPC was decreased as compared to transplantation of eEPCs alone. Regional wall motion of the left ventricle was measured using Magnetic Resonance Imaging. After injection of eEPC in the presence of EPO regional wall motion significantly improved as compared to injection of eEPCs or EPO alone.</p> <p>Conclusion</p> <p>Intramyocardial transplantation of eEPC in the presence of EPO during experimental MI improves regional wall motion. This was associated with an increased local inflammation, vasculogenesis and survival of the transplanted cells. Local application of EPO in addition to cell therapy may prove beneficial in myocardial remodeling.</p