Exact treatment of planar two-electron quantum dots: effects of anharmonicity on the complexity

Static properties of an anharmonic potential model for planar two-electron quantum dots are investigated using a method which allows for the exact representation of the matrix elements, including the full Coulombic electron - electron interaction. The anharmonic confining potential in combination with the interparticle Coulomb interaction affects the spectral properties of the system considerably as it implies total loss of separability of the system. Properties of the classical phase space, spectral measures of the chaoticity, as well as localization properties of the eigenstates corroborate this.Comment: 14 pages, 5 figure

Explicit schemes for time propagating many-body wavefunctions

Accurate theoretical data on many time-dependent processes in atomic and molecular physics and in chemistry require the direct numerical solution of the time-dependent Schr\"odinger equation, thereby motivating the development of very efficient time propagators. These usually involve the solution of very large systems of first order differential equations that are characterized by a high degree of stiffness. We analyze and compare the performance of the explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have exactly the same stability function, therefore sharing the same stability properties that turn out to be optimum. Their respective accuracy however differs significantly and depends on the physical situation involved. In order to test this accuracy, we use a predictor-corrector scheme in which the predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully implicit four-stage Radau IIA method of order 7. We consider two physical processes. The first one is the ionization of an atomic system by a short and intense electromagnetic pulse; the atomic systems include a one-dimensional Gaussian model potential as well as atomic hydrogen and helium, both in full dimensionality. The second process is the decoherence of two-electron quantum states when a time independent perturbation is applied to a planar two-electron quantum dot where both electrons are confined in an anharmonic potential. Even though the Hamiltonian of this system is time independent the corresponding differential equation shows a striking stiffness. For the one-dimensional Gaussian potential we discuss in detail the possibility of monitoring the time step for both explicit algorithms. In the other physical situations that are much more demanding in term of computations, we show that the accuracy of both algorithms depends strongly on the degree of stiffness of the problem.Comment: 24 pages, 14 Figure

Spectral data for doubly excited states of helium with non-zero total angular momentum

A spectral approach is used to evaluate energies and widths for a wide range of singlet and triplet resonance states of helium. Data for total angular momentum $L=1,...,4$ is presented for resonances up to below the 5th single ionization threshold. In addition the expectation value of $\cos(\theta_{12})$ is given for the calculated resonances.Comment: 35 pages, 16 tables, to be published in Atomic Data and Nuclear Data Table

Light flavor baryon spectrum with higher order hyperfine interactions

We study the spectrum of light flavor baryons in a quark-model framework by taking into account the order $\mathrm{O}(\alpha_s^2)$ hyperfine interactions due to two-gluon exchange between quarks. The calculated spectrum agree better with the experimental data than the results from hyperfine interactions with only one-gluon exchange. It is also shown that two-gluon exchange hyperfine interactions bring a significantly improved correction to the Gell-Mann--Okubo mass formula. Two-gluon exchange corrections on baryon excitations (including negative parity baryons) are also briefly discussed.Comment: 31 latex pages, final version in journal publicatio

Convexity-Increasing Morphs of Planar Graphs

We study the problem of convexifying drawings of planar graphs. Given any planar straight-line drawing of an internally 3-connected graph, we show how to morph the drawing to one with strictly convex faces while maintaining planarity at all times. Our morph is convexity-increasing, meaning that once an angle is convex, it remains convex. We give an efficient algorithm that constructs such a morph as a composition of a linear number of steps where each step either moves vertices along horizontal lines or moves vertices along vertical lines. Moreover, we show that a linear number of steps is worst-case optimal. To obtain our result, we use a well-known technique by Hong and Nagamochi for finding redrawings with convex faces while preserving y-coordinates. Using a variant of Tutte's graph drawing algorithm, we obtain a new proof of Hong and Nagamochi's result which comes with a better running time. This is of independent interest, as Hong and Nagamochi's technique serves as a building block in existing morphing algorithms.Comment: Preliminary version in Proc. WG 201

Endovaskuläre iliakale side-branch Stentgraft Implantation zur Behandlung isolierter, kombiniert infra-/juxtarenaler oder thorakoabdominaler Aneurysmata

Iliakalaneurysmata treten in den meisten Fällen (80%) in Kombination mit einem infrarenalen Bauchaortenaneurysma auf. Isolierte Iliakalaneurysmata sind selten und gehen mit einer Prävalenz von 0,008%-0,03% einher. Die schwerste Komplikation eines Iliakalaneurysmas besteht in seiner Ruptur (Mortalität bis zu 70%). Das Risiko wird entscheidend durch Größe, Morphologie und Wachstumstendenz des Aneurysmas bestimmt. Bei einer Aneurysmagröße von >4cm liegt das Rupturrisiko bei 15%. Durch die Entwicklung von Seitenarm- Endostentprothesen ist es möglich bei der endovaskulären Aneurysmaausschaltung von Iliakalaneurysmata die pelvine Perfusion zu erhalten. In dieser Arbeit wurden retrospektiv die Daten von 72 Patienten (66 Männer; 6 Frauen; Altersdurchschnitt 71 Jahre) ausgewertet, bei denen zwischen Dezember 2006 und Februar 2014 in der gefäßchirurgischen Abteilung des Universitätsklinikums in Regensburg der s-IBD implantiert werden sollte. Eingeschlossen wurden sowohl Patienten mit isolierten Iliakalaneurysmata (18,1%), als auch Patienten mit einer Kombination von iliakalen mit infrarenalen Aneurysmata (54,2%) oder iliakalen und juxtarenalen/thorakoabdominalen Aneurysmata (27,8%). Insgesamt wurden bei den 72 Patienten 99 Iliakalaneurysmata diagnostiziert. Es wurden dabei 85 IBDs mit AII-Stent implantiert. Behandelt wurden dabei Aneurysmata der AIC (74,7%), Aneurysmata der AIC und AII (20,2%) sowie isolierte Aneurysmata der AII (5,1%). Bei 12 der 99 Iliakalaneurysmata (12,1%) wurde die AII intendiert verschlossen. Der technische Erfolg der Implantation lag bei 94,9% (94 von 99 durchgeführten Interventionen). Die postoperative Offenheitsrate lag bei 96,4%. Am Ende des Beobachtungszeitraums (mittlere Verlaufsdauer 38 Monate) betrug die Offenheitsrate noch 92,8% (77 von 83 IBDs). 2 Patienten verstarben perioperativ (2,8%). Neben der geringen Letalität ging die Behandlung mit einer geringen Komplikations- und Reinterventionsrate einher. Ein Endoleak wurde achtmal (9,2%), ein Stentverschluss sechsmal (7,2%) und eine Stentstenose dreimal (3,6%) diagnostiziert. Eine Glutealclaudicatio trat bei 7 von 69 Patienten auf (10,2%). Bei allen Patienten war die pelvine Perfusion durch die AII nicht vollständig oder gar nicht erhalten. Eine Reintervention auf Grund der beschriebenen Komplikationen wurde achtmal durchgeführt (9,2%). Beim statistischen Vergleich zwischen Patienten mit Aneurysmata der AIC und Patienten mit Aneurysmata der AII (isoliert oder kombiniert) zeigte sich, dass die Behandlung eines Aneurysmas der AII mit dem IBD nicht mit einem höheren Risiko an postoperativen Komplikationen einhergeht. Es konnte außerdem gezeigt werden, dass die kombinierte Therapie von Iliakalaneurysmata und Aortenaneurysmata bei erhaltener pelviner Perfusion nicht das Risiko der perioperativen Letalität oder der spinalen Ischämie erhöht. Die erhöhte Letalität im Verlauf bei Patienten mit thorakoabdominalen Aneurysmata ist am ehesten durch die erhöhte Gesamtmorbidität dieser Patientengruppe bedingt

Diffusion-weighted imaging in oral squamous cell carcinoma using 3 Tesla MRI: is there a chance for preoperative discrimination between benign and malignant lymph nodes in daily clinical routine?

Background Preoperative staging of cervical lymph nodes is important to determine the extent of neck dissection in patients with oral squamous cell carcinoma (OSCC). Purpose To evaluate whether a preoperative discrimination of benign and malignant cervical lymph nodes with diffusion-weighted imaging (DWI) (3T) is feasible for clinical application. Material and Methods Forty-five patients with histological proven OSCC underwent preoperative 3T-MRI. DWI (b=0, 500, and 1000s/mm(2)) was added to the standard magnetic resonance imaging (MRI) protocol. Mean apparent diffusion coefficients (ADC(mean)) were measured for lymph nodes with 3mm or more in short axis by two independent readers. Finally, these results were matched with histology. Results Mean ADC was significantly higher for malignant than for benign nodes (1.1430.188 * 10(-3) mm(2)/s vs. 0.987 +/- 0.215 * 10(-3) mm(2)/s). Using an ADC value of 0.994 * 10(-3) mm(2)/s as threshold results in a sensitivity of 80%, specificity of 65%, positive predictive value of 31%, and negative predictive value of 93%. Conclusion Due to a limited sensitivity and specificity DWI alone is not suitable to reliably discriminate benign from malignant cervical lymph nodes in daily clinical routine. Hence, the preoperative determination of the extent of neck dissection on the basis of ADC measurements is not meaningful

Influence of retardation in the scattering of ultracold atoms by conducting nanowires

We study low-energy scattering of a neutral atom by a perfectly conducting cylindrical nanowire. Based on the exact atom-wire potential given recently by Eberlein and Zietal [ Phys. Rev. A 80 012504 (2009)] we derive tractable expressions for both the nonretarded van der Waals limit and the highly retarded limit as well as a realistic description of the transition between these two limits. For real atoms and wire radii greater than a few atomic units, the nonretarded van der Waals limit is insufficient, whereas the highly retarded limit of the atom-wire potential gives an accurate description of low-energy elastic scattering and absorption cross sections

Exact treatment of planar two-electron quantum dots: Effects of anharmonicity on the complexity:

The static properties of an anharmonic potential model for planar two-electron quantum dots are investigated using a method that allows for the exact representation of the matrix elements, including the full Coulombic electron-electron interaction. A quartic perturbation of the harmonic confining potential in combination with the interparticle Coulomb interaction affects the spectral properties of the system considerably as it implies total loss of separability in the dynamics. Consequently, the classical phase space is mixed regular-chaotic and standard spectral measures of quantum chaos indicate an intermediate degree of complexity. Apart from the prompt transition from a regular to a moderately chaotic regime for weak quartic perturbation, the complexity of the system appears to be insensitive to the strength of the quartic potential. DOI: 10.1103/PhysRevB.87.15541