1,227 research outputs found

    Improving quality of cervical cancer care with (inter)national cancer registry data

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    Cervical cancer is relatively rare in the Netherlands, with ÔÇśjustÔÇÖ eight hundred diagnoses per year. However, it is the fourth most common cancer-related cause of death worldwide. In this thesis, we showed that survival rates of women with cervical cancer have increased in the Netherlands, over the past decades. Unfortunately, this does not go for older women. If cervical cancer is detected at an early stage, treatment usually consists of a radical hysterectomy. This thesis shows that, for the prognosis, it does not matter whether that surgical procedure is performed by a large incision into the abdominal cavity, or by keyhole surgery. In one-third of the surgical procedures, a complication occurs within 30 days, although percentages differ among medical centres.Whether a patient with cervical cancer will survive, depends for an important part on whether the disease has spread to the lymph nodes. So-called lymph node metastases negatively impact prognosis. Therefore, it is customary to remove the pelvic lymph nodes during radical hysterectomy. Research in this thesis shows that a particular group of women seems to have such a low risk of lymph node metastasis, that they could probably do with less extensive lymph node surgery. If there is a strong suspicion of lymph node metastasis before surgery, the patient is often not treated surgically, but by radiotherapy. In case, unexpectedly, lymph node metastases are found during surgery, it does not seem to matter, for the prognosis of the patient, whether the radical hysterectomy is completed or not

    Impact of the capture time on the series resistance of quantum-well diode lasers

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    Electrons and holes injected into a semiconductor heterostructure containing quantum wellsare captured with a finite time. We show theoretically that this very fact can cause a considerableexcess contribution to the series resistivity and this is one of the main limiting factors to higherefficiency for GaAs based high-power lasers. The theory combines a standard microscopic-basedmodel for the capture-escape processes in the quantum well with a drift-diffusion description ofcurrent flow outside the quantum well. Simulations of five GaAs-based devices differing in theirAl-content reveal the root-cause of the unexpected and until now unexplained increase of theseries resistance with decreasing heat sink temperature measured recently. The finite capturetime results in resistances in excess of the bulk layer resistances (decreasing with increasingtemperature) from 1 m╬ę up to 30 m╬ę in good agreement with experiment

    Dynamics in high-power diode lasers

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    High-power broad-area diode lasers (BALs) exhibit chaotic spatio-temporal dynamics above threshold. Under high power operation, where they emit tens of watts output, large amounts of heat are generated, with significant impact on the laser operation. We incorporate heating effects into a dynamical electro-optical (EO) model for the optical field and carrier dynamics along the quantum-well active zone of the laser. Thereby we effectively couple the EO and heat-transport (HT) solvers. Thermal lensing is included by a thermally-induced contribution to the index profile. The heat sources obtained with the dynamic EO-solver exhibit strong variations on short time scales, which however have only a marginal impact on the temperature distribution. We consider two limits: First, the static HT-problem, with time-averaged heat sources, which is solved iteratively together with the EO solver. Second, under short pulse operation the thermally induced index distribution can be obtained by neglecting heat flow. Although the temperature increase is small, a waveguide is introduced here within a few-ns-long pulse resulting in significant near field narrowing. We further show that a beam propagating in a waveguide structure utilized for BA lasers does not undergo filamentation due to spatial holeburning. Moreover, our results indicate that in BALs a clear optical mode structure is visible which is neither destroyed by the dynamics nor by longitudinal effects

    Beam Position Determination using Tracks

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    Track-based algorithms to determine the LHC beam position and profile at the CMS collision point are described. Only track information is used and no reconstruction of the primary event vertex is required. With only about thousand tracks, a statistical precision of 2 microns for the transverse beam position is achieved, assuming a well aligned detector. The algorithms are simple and fast, and can be used to monitor the beam in real time. A method to determine the track impact parameter resolution using the beam position and beam width calculation is also presented

    Semiconductor Laser Linewidth Theory Revisited

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    More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a self-contained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the time-dependent coupled-wave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission (KK-factor) and the effective ╬▒\alpha-factor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multi-section cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the so-called chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a two-section distributed Bragg reflector laser.Comment: semiconductor laser, spectral linewidth, coupled-wave equations, traveling wave model, noise, Langevin equations, Henry factor, Petermann factor, chirp reduction factor, population inversion facto

    Semiconductor laser linewidth theory revisited

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    More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a self-contained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the time-dependent coupled-wave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission (K-factor) and the effective Alpha-factor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multi-section cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the so-called chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a two-section distributed Bragg reflector laser

    Modeling of current spreading in high-power broad-area lasers and its impact on the lateral far field divergence

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    The effect of current spreading on the lateral far-field divergence of high-power broad-area lasers is investigated with a time-dependent model using different descriptions for the injection of carriers into the active region. Most simulation tools simply assume a spatially constant injection current density below the contact stripe and a vanishing current density beside. Within the drift-diffusion approach, however, the injected current density is obtained from the gradient of the quasi-Fermi potential of the holes, which solves a Laplace equation in the p-doped region if recombination is neglected. We compare an approximate solution of the Laplace equation with the exact solution and show that for the exact solution the highest far-field divergence is obtained. We conclude that an advanced modeling of the profiles of the injection current densities is necessary for a correct description of far-field blooming in broad-area lasers

    Simulation and analysis of high-brightness tapered ridge-waveguide lasers

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    In this work, a simulation-based analysis of a CW-driven tapered ridge-waveguide laser design is presented. Measurements of these devices delivered high lateral brightness values of 4 W ┬Ě mm - 1mrad - 1 at 2.5W optical output power. First, active laser simulations are performed to reproduce these results. Next, the resulting complex valued intra-cavity refractive index distributions are the basis for a modal and beam propagation analysis, which demonstrates the working principle and limitation of the underlying lateral mode filter effect. Finally, the gained understanding is the foundation for further design improvements leading to lateral brightness values of up to 10 W ┬Ě mm - 1mrad - 1 predicted by simulations

    Die R├Âmer im Hessischen Ried : Arch├Ąologie einer Kulturlandschaft ├╝ber f├╝nf Jahrhunderte

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    Das Hessische Ried war nur d├╝nn besiedelt, als die R├Âmer kurz vor der Zeitenwende die Garnisonsstadt Mogontiacum/Mainz gr├╝ndeten. Gelegen im rechtsrheinischen Vorfeld der neuen Metropole, profitierte das Ried von der Wirtschaftskraft der dort stationierten Legionen, denen es als Nutzland und Man├Âvergebiet diente. Vollst├Ąndig erschlossen wurde das Gebiet aber erst durch die zivile Besiedlungsphase im fr├╝hen zweiten Jahrhundert n. Chr. mit der Gr├╝ndung von D├Ârfern und zahlreichen Gutsh├Âfen. Nach zwischenzeitlichem R├╝ckgang der Besiedlung erlebte das Ried im vierten Jahrhundert eine neue Bl├╝tezeit. Das Institut f├╝r Arch├Ąologische Wissenschaften hat die Entwicklung dieser Region bis um 500 n. Chr. in einem mehrj├Ąhrigen Projekt rekonstruiert. Nach dem rheinischen Kohleabbaugebiet ist das Hessische Ried die am intensivsten erforschte Landschaft im r├Âmischen Deutschland
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