162 research outputs found
Diagrammatic approach to coherent backscattering of laser light by cold atoms: Double scattering revisited
We present a diagrammatic derivation of the coherent backscattering spectrum
from two two-level atoms using the pump-probe approach, wherein the multiple
scattering signal is deduced from single-atom responses, and provide a physical
interpretation of the single-atom building blocks.Comment: 16 pages, 7 figure
Interference pattern with a dark center from two atoms driven by a coherent laser field
In a recent paper Meyer and Yeoman [Phys. Rev. Lett. 79, 2650 (1997)] have shown that the resonance fluorescence from two atoms placed in a cavity and driven by an incoherent field can produce an interference pattern with a dark center. We study the fluorescence from two coherently driven atoms in free space and show that this system can also produce an interference pattern with a dark center. This happens when the atoms are in nonequivalent positions in the driving: field, i.e., the atoms experience different intensities and phases of the driving field. We discuss the role of the interatomic interactions in this process and find that the interference pattern with a dark center results from the participation of the antisymmetric state in the dynamics of the driven two-atom system
Resonant Energy Exchange between Atoms in Dispersing and Absorbing Surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, a master equation describing both the resonant dipole-dipole interaction
(RDDI) and the resonant atom-field interaction (RAFI) in the presence of
dispersing and absorbing macroscopic bodies is derived, with the relevant
couplings being expressed in terms of the surroundings-assisted Green tensor.
It is shown that under certain conditions the RDDI can be regarded as being
governed by an effective Hamiltonian. The theory, which applies to both weak
and strong atom-field coupling, is used to study the resonant energy exchange
between two (two-level) atoms sharing initially a single excitation. In
particular, it is shown that in the regime of weak atom-field coupling there is
a time window, where the energy transfer follows a transfer-rate law of the
type obtained by ordinary second-order perturbation theory. Finally, the
spectrum of the light emitted during the energy transfer is studied and the
line splittings are discussed.Comment: 9 pages, 5 figs, Proceedings of ICQO'2002, Raubichi, to appear in
Optics and Spectroscop
Comparison of sitting position vs. non sitting position the resection of brain metastases in the posterior fossa: surgical and functional outcome in a contemporary cohort [Abstract]
Non-equilibrium entangled steady state of two independent two-level systems
We determine and study the steady state of two independent two-level systems
weakly coupled to a stationary non-equilibrium environment. Whereas this
bipartite state is necessarily uncorrelated if the splitting energies of the
two-level systems are different from each other, it can be entangled if they
are equal. For identical two-level systems interacting with two bosonic heat
baths at different temperatures, we discuss the influence of the baths
temperatures and coupling parameters on their entanglement. Geometric
properties, such as the baths dimensionalities and the distance between the
two-level systems, are relevant. A regime is found where the steady state is a
statistical mixture of the product ground state and of the entangled singlet
state with respective weights 2/3 and 1/3
Cathedral engagement with young people
The Archbishops’ Commission on Cathedrals (1994) identified education as among the crucial purposes of cathedrals. This chapter analyzes the websites of fifteen cathedrals within the most urban dioceses of the Church of England and the Church in Wales in order to ascertain the variety of ways in which cathedrals are advancing the educational work of the Church in urban areas. The analysis distinguishes between four primary areas of activity, characterized as concerning school-related education, faith-related education, visitor-related education, and music-related education. Each of these four areas is illustrated by a case study profiling current practice
Spontaneous emission of an atom in front of a mirror
Motivated by a recent experiment [J. Eschner {\it et al.}, Nature {\bf 413},
495 (2001)], we now present a theoretical study on the fluorescence of an atom
in front of a mirror. On the assumption that the presence of the distant mirror
and a lens imposes boundary conditions on the electric field in a plane close
to the atom, we derive the intensities of the emitted light as a function of an
effective atom-mirror distance. The results obtained are in good agreement with
the experimental findings.Comment: 8 pages, 6 figures, revised version, references adde
Prospective Multicenter Trial of Cervical Arthroplasty with the ROTAIO® Cervical Disc Prosthesis.
STUDY DESIGN
Clinical observational study.
OBJECTIVE
The ROTAIO® cervical disc prosthesis is a novel unconstrained implant with a variable center of rotation aiming at physiological motion. The objective of this multicenter prospective trial was to evaluate clinical outcome and complications within 2 years.
MATERIAL AND METHODS
120 patients (72 females and 48 males with median age of 43.0 years [23-60 yrs] underwent ACDA (ROTAIO®, SIGNUS Medical, Alzenau, Germany) and were prospectively followed for 24 months. Preoperative complaints were mainly associated with radiculopathy (n = 104) or myelopathy (n=16). There were 108 monosegmental and 12 bisegmental procedures including 6 hybrid constructs. Clinical outcome was evaluated at 3, 12 and 24 months in 100%, 96% and 77% of the cohort by VAS, NDI, WL-26, Patient`s Satisfaction Index (PSI), SF-36, Nurick Score, mJOA, Composite Success Rate, complications, patient`s overall satisfaction and analgesics use.
RESULTS
Highly significant clinical improvements were observed according to NDI and VAS (P < .0001 (arm); P < .001 (neck); P = .002 (head)) at all time points. Analgetic use could be reduced in 87.1 to 95.2%. Doctor`s visits have been reduced in 93.8% after 24Â months. Patient`s overall satisfaction was high with 78.4 to 83.5% of patients. The composite success rate was 77.5% after 12Â months and 76.9% after 24Â months. There were no major complications in this series. Slight subsidence of the prosthesis was observed in 2 patients and 3 patients demonstrated fusion after 24Â months. 2 patients developed symptomatic foraminal stenosis, so that implant removal and fusion was performed resulting in a revision rate of 1.7% in 2Â years.
CONCLUSION
The ROTAIO® cervical disc prosthesis is a safe and efficient treatment option for symptomatic degenerative disc disease demonstrating highly significant clinical improvement and high patient`s overall satisfaction with very low revision rates at 2 years
Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, equations of motion and an effective Hamiltonian for treating both the
resonant dipole-dipole interaction between two-level atoms and the resonant
atom-field interaction are derived, which can suitably be used for studying the
influence of arbitrary dispersing and absorbing material surroundings on these
interactions. The theory is applied to the study of the transient behavior of
two atoms that initially share a single excitation, with special emphasis on
the role of the two competing processes of virtual and real photon exchange in
the energy transfer between the atoms. In particular, it is shown that for weak
atom-field interaction there is a time window, where the energy transfer
follows a rate regime of the type obtained by ordinary second-order
perturbation theory. Finally, the resonant dipole-dipole interaction is shown
to give rise to a doublet spectrum of the emitted light for weak atom-field
interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE
Prospective Multicenter Trial of Cervical Arthroplasty With the ROTAIO® Cervical Disc Prosthesis
Objective
Anterior Cervical Discectomy and Arthroplasty (ACDA) is an established treatment for degenerative cervical disc disease and seems to be an alternative to fusion in minimizing the risk of Adjacent Segment Disease (ASD). The ROTAIO® cervical disc prosthesis is a novel unconstrained implant with a variable center of rotation aiming at physiological motion. The objective of this multicenter prospective trial was to evaluate clinical outcome and complications within 2 years.
Material and Methods
120 patients (72 females and 48 males with a median age of 43.0 years; range: 23 to 60 years) underwent ACDA (ROTAIO®, SIGNUS Medical, Alzenau, Germany) and were prospectively followed for 24 months. Preoperative complaints were mainly associated with radiculopathy (n=104) or myelopathy (n=16). There were 108 monosegmental and 12 bisegmental procedures including 6 hybrid constructs.
Clinical outcome was evaluated at 3, 12 and 24 months by the Visual Analogue Scale (VAS) for head, neck and arm pain, the Neck Disability Index (NDI), the Work Limitation Questionnaire (WL-26), the Patient`s Satisfaction Index (PSI) and a Quality of Life Questionnaire (SF-36). The Nurick Score, the Modified Japanese Orthopaedic Association Score (mJOA) plus a Composite Success Rate have been additionally applied. Finally, complications, the patient`s overall satisfaction and the amount of analgesics were assessed.
Results
Highly significant clinical improvements were observed according to NDI and VAS (p<0.0001 (arm); p<0.001 (neck); p=0.002 (head)) at all postoperative time points. Analgetic medication could be reduced after 3 months in 91.3%, after 12 months in 87.1% and after 24 months in 95.2% of patients. Doctor`s visits for cervical spine problems have been reduced in 93.8% after 24 months.
Patient`s overall satisfaction was high after 3, 12 and 24 months with 83.5%, 78.4% and 79.1% of patients, while 4.1%, 6.8% and 7.0% respectively were not satisfied. The composite success rate was 77.5% after 12 months and 76.9% after 24 months. There were no major complications in this series. Slight subsidence of the prosthesis was observed in 2 patients and 3 patients demonstrated fusion after 24 months. 2 patients developed symptomatic foraminal stenosis, so that implant removal and fusion was performed.
Conclusion
The ROTAIO® cervical disc prosthesis is a safe and efficient treatment option for symptomatic degenerative disc disease demonstrating excellent clinical results at 2 years. Outcome proves to be stable over time with very low revision rates
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