A time-dependent Casimir–Polder force is shown to arise during the time evolution of a partially dressed two-level atom. The partially dressed atom is obtained by a rapid change of an atomic ...parameter such as its transition frequency, due to the action of some external agent. The electromagnetic field fluctuations around the atom, averaged over the solid angle for simplicity, are calculated as a function of time, and it is shown that the interaction energy with a second atom yields a dynamical Casimir–Polder potential between the two atoms.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We calculate the Casimir–Polder intermolecular potential using an effective Hamiltonian recently introduced. We show that the potential can be expressed in terms of the dynamical polarizabilities of ...the two atoms and the equal-time spatial correlation of the electric field in the vacuum state. This gives support to an interesting physical model recently proposed in the literature, where the potential is obtained from the classical interaction between the instantaneous atomic dipoles induced and correlated by the vacuum fluctuations. Also, the results obtained suggest a more general validity of this intuitive model, for example, when external boundaries or thermal fields are present.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Background The frequency of small-bowel mucosal changes in patients with portal hypertension is not known. The objective of the study is to better define the mucosal abnormalities of portal ...hypertensive enteropathy (PHE) and to determine whether these findings are associated with the severity of liver disease, esophageal varices, portal gastropathy, portal colonopathy, or other clinical characteristics. Methods We compared the medical records of 37 patients with cirrhosis and portal hypertension with 34 control patients who underwent capsule endoscopy over a 3-year period. Results Mucosal changes were found to be significantly more common in the cirrhotic patients than in the control patients (67.5% vs. 0, p < 0.001). The lesions included telangiectasias or angiodysplastic-like lesions in 9 (24.3%) patients, red spots in 23 (62.2%), and varices in 3 (8.1%). Active bleeding was seen during endoscopic examinations in 4 (10.8%) patients. A comparison of patients with and those without PHE showed that 2+ or larger esophageal varices, portal gastropathy, portal colonopathy, and Child-Pugh class C cirrhosis were all significantly associated with PHE. There were no differences between these two groups of patients with regard to the etiology of cirrhosis, gender, or history of esophageal variceal bleeding Conclusions Mucosal abnormalities in portal jejunopathy include edema, erythema, and vascular lesions findings. A standardized grading system to classify the endoscopic appearance and the severity of portal enteropathy is proposed. The clinical import of these changes remains to be explained.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The three-body Casimir-Polder potential between one excited and two ground-state atoms is evaluated. A physical model based on the dressed field correlations of vacuum fluctuations is used, ...generalizing a model previously introduced for three ground-state atoms. Although the three-body potential with one excited atom is already known in the literature, our model gives new insights on the nature of non-additive Casimir-Polder forces with one or more excited atoms.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
We show that it is possible to use a piecewise constant Hamiltonian to describe the main features of the dynamics of an atom interacting with a laser field. In particular we show that using this ...approximation we are able to give a good description of the ionization signal, of the HHG spectra and of the attosecond pulses generated by the radiating electron. Finally, we give an explicit formula to evaluate the ionization rate in the time dependent laser field. This formula, which is a generalization of the Landau formula for the ionization rate of an atom in a static electric field, fairly well reproduces the numerical ionization rates for a broad range of laser frequency and intensity. The main advantage of this formula is that it can be used well beyond the limits of the quasi-static formula for the ionization rate of an atom.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
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