The bright and the dark sides of brachytherapy: mechanisms of stenosis reduction and findings of intracoronary β-radiation therapy revealed by IVUS-3D and QCA

Sincethe first percutaneous coronary intervention, 24 years ago, the field of interventional cardiology has continued to grow rapidly. Although PTCA has demonstrated superiority to medical therapy in alleviating angina, restenosis and acute closure of the treated vessel remained major limitations. Stent has improved both problems by preventing residual dissection, elastic recoil and negative remodeling. However, the occurrence of restenosis after stenting remains unresolved. Furthermore, in-stent restenosis has become a new enemy in the field of interventional cardiology, since the conventional treatment of in-stent restenosis is rather disappointing with high restenosis rates (around 30 - 70%). Therefore, the holy grail to overcome this immense enemy went unabated. Intracoronary brachytherapy is a powerful therapy to prevent restenosis after percutaneous transluminal coronary intervention. The purpose of this thesis is to explore the mechanism of action of intracoronary radiation and the problems related to this procedure. For this purpose, three-dimensional intravascular ultrasound (IVUS) and quantitative coronary angiography (QCA) were applied as investigational tools. This thesis consists of 2 parts; the first part deals with the positive aspect of intracoronary brachytherapy which explains its increasing application (Chapter 2) and its mechanistic interpretation (Chapters 3-7). The second part reports on the dark sides of intracoronary brachytherapy (Chapters 8-12)

Entanglement of orbital angular momentum states between an ensemble of cold atoms and a photon

Recently, atomic ensemble and single photons were successfully entangled by using collective enhancement [D. N. Matsukevich, \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 040405(2005).], where atomic internal states and photonic polarization states were correlated in nonlocal manner. Here we experimentally clarified that in an ensemble of atoms and a photon system, there also exists an entanglement concerned with spatial degrees of freedom. Generation of higher-dimensional entanglement between remote atomic ensemble and an application to condensed matter physics are also discussed.Comment: 5 pages, 3 figure

Temperature rise measurement for power-loss comparison of an aluminum electrolytic capacitor between sinusoidal and square-wave current injections

DC-link capacitors are a major factor of degrading reliability of power electric converters because they usually have a shorter lifetime and higher failure rate than those of semiconductor devices or magnetic devices. Characteristics of the capacitors are usually evaluated by a single sinusoidal current waveform. However, actual current flowing out of the converter into the capacitor is a modulated square current waveform. This paper provides experimental comparison of the power loss dissipated in an aluminum electrolytic capacitor between sinusoidal and square-wave current injections. Power loss is estimated by temperature rise of the capacitor. Experimental results confirm that power losses of the square-wave current injection were always lower than those of the sinusoidal current injection by 10–20%. Moreover, the power losses of the square-wave current injection can be estimated by a synthesis of fundamental and harmonic currents based on the Fourier series expansion, which brings a high accuracy less than 1% when more than fifth harmonic current is introduced. This comparison will be useful for estimating power loss and life time of electrolytic capacitors

Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate

We construct a Mach-Zehnder interferometer using Bose-Einstein condensed rubidium atoms and optical Bragg diffraction. In contrast to interferometers based on normal diffraction, where only a small percentage of the atoms contribute to the signal, our Bragg diffraction interferometer uses all the condensate atoms. The condensate coherence properties and high phase-space density result in an interference pattern of nearly 100% contrast. In principle, the enclosed area of the interferometer may be arbitrarily large, making it an ideal tool that could be used in the detection of vortices, or possibly even gravitational waves.Comment: 10 pages, 3 figures, Quantum Electronics and Laser Science Conference 1999, Postdeadline papers QPD12-

Does matter wave amplification work for fermions?

We discuss the relationship between bosonic stimulation, density fluctuations, and matter wave gratings. It is shown that enhanced stimulated scattering, matter wave amplification and atomic four-wave mixing are in principle possible for fermionic or non-degenerate samples if they are prepared in a cooperative state. In practice, there are limitations by short coherence times.Comment: 5 pages, 1 figure

Spontaneous emission of atoms via collisions of Bose-Einstein condensates

The widely used Gross-Pitaevskii equation treats only coherent aspects of the evolution of a Bose-Einstein condensate. However, inevitably some atoms scatter out of the condensate. We have developed a method, based on the field theory formulation, describing the dynamics of incoherent processes which are due to elastic collisions. We can therefore treat processes of spontaneous emission of atoms into the empty modes, as opposed to stimulated processes, which require non-zero initial occupation. In this article we study two counter-propagating plane waves of atoms, calculating the full dynamics of mode occupation, as well as the statistics of scattered atoms. The more realistic case of Gaussian wavepackets is also analyzed.Comment: 5 pages, 2 figure

Coherence properties of an atom laser

We study the coherence properties of an atom laser, which operates by extracting atoms from a gaseous Bose-Einstein condensate via a two-photon Raman process, by analyzing a recent experiment. We obtain good agreement with the experimental data by solving the time-dependent Gross-Pitaevskii equation in three dimensions both numerically and with a Thomas-Fermi model. The coherence length is strongly affected by the space-dependent phase developed by the condensate when the trapping potential is turned off.Comment: 11 pages, 2 Postscript figure

Creating massive entanglement of Bose condensed atoms

We propose a direct, coherent coupling scheme that can create massively entangled states of Bose-Einstein condensed atoms. Our idea is based on an effective interaction between two atoms from coherent Raman processes through a (two atom) molecular intermediate state. We compare our scheme with other recent proposals for generation of massive entanglement of Bose condensed atoms.Comment: 5 pages, 3 figures; Updated figure 3(a), original was "noisy

Optical Generation of Vortices in trapped Bose-Einstein Condensates

We demonstrate numerically the efficient generation of vortices in Bose-Einstein condensates (BEC) by using a ``phase imprinting'' method. The method consist of passing a far off resonant laser pulse through an absorption plate with azimuthally dependent absorption coefficient, imaging the laser beam onto a BEC, and thus creating the corresponding non-dissipative Stark shift potential and condensate phase shift. In our calculations we take into account experimental imperfections. We also propose an interference method to detect vortices by coherently pushing part of the condensate using optically induced Bragg scattering.Comment: 8 pages, 4 figure

Talbot Oscillations and Periodic Focusing in a One-Dimensional Condensate

An exact theory for the density of a one-dimensional Bose-Einstein condensate with hard core particle interactions is developed in second quantization and applied to the scattering of the condensate by a spatially periodic impulse potential. The boson problem is mapped onto a system of free fermions obeying the Pauli exclusion principle to facilitate the calculation. The density exhibits a spatial focusing of the probability density as well as a periodic self-imaging in time, or Talbot effect. Furthermore, the transition from single particle to many body effects can be measured by observing the decay of the modulated condensate density pattern in time. The connection of these results to classical and atom optical phase gratings is made explicit