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O Keller

Publications and source records attributed to O Keller.

At least 19 recordsLinked to original sources
PubMed2003

Near-field optics and quantum optics: an assignation arranged by four kinds of photons.

In the process of emergence a photon emitted from an atom (or a molecule) is usually no better localized in space than to the near-field zone of the source. Near-field optics therefore is of central importance for understanding fundamental statistical aspects related to single-photon tunnelling, the space-time description of photon dynamics, and the photon position-operator problem. In the present work an attempt is made to study the microscopic near-field optical interaction from a quantum statistical point of view. In near-field quantum electrodynamics (QED) scalar and longitudinal photons always are involved and this makes the covariant formulation of QED attractive also in the low-energy regime. We show that the Lorenz gauge condition on the global state vector relates to the near-field electrodynamics of the d-photons. The gauge photon is shown to be of no importance in near-field interactions. To understand the role of the lack of photon localizability we finally study near-field quantum optical correlations in a new so-called propagator gauge.

Lasers↗
PubMed2003

Electrodynamic interaction between two atoms in near-field contact.

A theoretical study of elements of the quantum electrodynamic interaction between two single-electron atoms in near-field contact is presented. The framework of the study is an electromagnetic propagator formalism that allows one to describe the near-field space-time interaction in such a manner that the Einstein causality and lack of photon localizability are manifest. First we set up the atom-field Hamiltonian in the so-called G-gauge, starting from the Coulomb Hamiltonian, and thereafter we show that this leads to a correct propagator description for the retarded part of the transverse electromagnetic field (operator). In the G-gauge approach, renormalization of the two-particle energy level structure stemming from the transverse self-field occurs. The intraparticle renormalization is calculated for a three-level atom (it is trivial for a two-level atom), and the interparticle renormalization, which depends on the atomic separation, is determined for two two-level atoms. The magnitude of the energy renormalization is always finite in our theory because we do not consider the atoms to be point-like objects from an electromagnetic point of view. Throughout, we relate our G-gauge formalism to the multipole theory often used in studies of interatomic electrodynamics.

Journal Article↗
PubMed2001

On the quantum physical relation between photon tunnelling and near-field optics.

The standard theory of optical tunnelling based on a mathematical analogy between the time-independent one-particle Schrödinger equation describing electron tunnelling and the Helmholtz equation for the macroscopic electric field is criticized. In a classical perspective photons are related to the dynamics of the transverse part of the electromagnetic field, and with the assumption that the electrons in a coupled photon-atom system are driven in a linear fashion by the field, a rigorous integro-differential equation for the transverse field is established. In the near-field zone of matter a transverse self-field exists and this may cause the appearance of superluminality in optical tunnelling. In the wake of a brief review of the space-time dynamics of free photons, a first-quantized description of the birth process of a single polychromatic photon in the near-field region of an active atom (molecule, mesoscopic particle) is presented, and afterwards the link between photon localizability, Einstein causality and near-field photon tunnelling is discussed. On the basis of a new one-photon quantum theory of near-field scattering from a microscopic (or mesoscopic) object, it is shown that photon tunnelling always appears in photon-atom scattering. A first-order Born approximation cannot capture the phenomenon, however. The emergence of the energy wave function of the scattered photon is followed in space and time.

Journal Article↗
PubMed2001

Superluminal interactions in near-field optics.

The fact that photons emitted from an electric-dipole active atom cannot be spatially localized better than to the near-field zone of the atom is seen as the origin of genuine superluminality. By means of a simple model dipole current density the general theory is used to demonstrate numerically how superluminality enters the near-field dynamics, and how from a measurement one could be tempted to believe that superluminal propagation effects occur. Furthermore, it is shown how for source-detector distances larger than a pulse length one should be able to divide the pulse into two separate parts: one purely superluminal part arising solely in the non-local generation process of the field, and another part seemingly propagating with superluminal speed. We comment on different velocity analyses, and we argue that the only fundamental velocity entering the problem is the vacuum velocity of light, which in a measurement would appear as the velocity of the trailing edge of the pulse.

Journal Article↗
PubMed1998

[Diagnostic costs for ambulatory care patients].

Few analyses of the costs of diagnostic plans have been published. We have determined and analyzed the diagnostic costs of 1000 consecutively evaluated patients at the medical outpatient clinic. A data base was developed for this purpose. Based on the itemized tarif the total costs amounted to 622,553.25 SFR. Medical services (consultations) required 20 per cent of this sum, laboratory services and technical investigations 40 per cent each. The average number of consultations per patient was 2.83 +/- 1.85. As expected the first consultation was the most expensive. It amounted on the average to 350.-SFR, 54% of which were used for laboratory and 27% for technical procedures. Chest X-ray, ECG, abdominal ultrasound and upper gastrointestinal endoscopy caused about 20% of the total diagnostic costs. Cost reduction could probably be achieved by using more stringent indications for laboratory and technical services.

Adolescent↗
PubMed1998

[Reduced visual capacity increases the risk of accidents in street traffic].

BACKGROUND: This study was carried out to investigate the relationship between the frequency of traffic accidents and impaired vision. MATERIALS AND METHODS: Seven hundred and fifty-four drivers involved in accidents were recruited, in addition to 250 accident-free drivers similar in age and driving experience as an control group. The age distribution of the persons involved in traffic accidents (mean 56.3 years) was similar to that of the control group (mean 57.7 years), the difference was not statistically significant. Both groups underwent a complete ophthalmological examination. RESULTS: All three types of accidents (night-time accidents, violations of right of way, accidents during an overtaking manoeuvre) had a statistically significantly higher incidence of reduced photopic visual acuity, mesopic vision and an increased sensitivity to glare. Some other visual functions were also abnormal, with differences according to the type of accident. In particular, there were noticeable differences between the control group and those who were involved in night-time accidents regarding mesopic vision and sensitivity to glare. Concerning mesopic vision, 15% of the 261 persons involved in night-time accidents did not reach the contrast limit of 1:5; with glare, 20.7% failed. In comparison 4% of the control group reached this critical limit without glare and 7.6% with glare. These differences are highly statistically significant. In contrast to these findings, many of the drivers involved in accidents assessed their own visual capability as "excellent". CONCLUSIONS: The results of this study show that reduced mesopic vision and increased sensitivity to glare are accompanied by an increased risk of night-time accidents (for example, collisions with a non-illuminated obstacle). This emphasizes the importance of regular ophthalmological check-ups including visual functions such as mesopic vision and sensitivity to glare, which currently are not required by the traffic laws in Germany.

Accidents, Traffic↗
PubMed1996

[Colorectal carcinoma. Which factors are decisive for development of postoperative complications?].

This retrospective study analyses the prognostic effect of different factors on morbidity and lethality based on selected, primarily resecting colon carcinoma operations (n = 222). In all, 12.2% of our operations were performed under emergency conditions. The total complication rate was 31.5%, the lethality rate 7.7%. The left hemicolectomy cases showed the highest morbidity (48.4%), the rectum amputation the highest lethality (11.8%). Tumour staging tumour differentiation and the sex of the patient showed no significant influence on the postoperative morbidity and lethality. However, a correlation was proved between the age of the patient, tumour localisation, co-morbidity, duration of operation and the conditions under which the operation was performed (emergency or elective), on the one hand, and morbidity and lethality on the other.

Adult↗
PubMed1995

Recovery from rhabdomyolysis after allogeneic BMT: report of a case with speculation on causation.

A case of fulminant rhabdomyolysis occurring 4 months after allogeneic BMT for CML is reported. The patient developed rhabdomyolysis following the empiric institution of antibacterial and anti-tuberculous medication. His inpatient course was complicated by the development of acute anuric renal failure and a severe myopathy. With aggressive supportive care, both of these complications resolved, making this patient the only reported survivor of rhabdomyolysis occurring after BMT.

Bone Marrow Transplantation↗