Killing Tensors in Koutras-McIntosh Spacetimes

This thesis is concerned with the (non)existence of Killing Tensors in Koutras-McIntosh spacetimes. Killing tensors are of particular interest in general relativity, because these correspond to conserved quantities for the geodesic motion. For instance, Carter found such a conserved quantity in the Kerr metric which he used to explicitly integrate the geodesic equations. The equation defining a Killing tensor is actually an overdetermined linear first order partial differential equation. We shall study the Killing equation using methods from the geometric theory of PDEs. More precisely, we use Cartan's prolongation method to prove the (non)existence of Killing tensors in several Koutras-McIntosh spacetimes. A subclass of the Koutras--McIntosh spacetimes are the conformally flat pp-waves. We show that a generic conf. flat pp-wave has an irreducible Killing 2-tensor, which reproves a result obtained by Keane and Tupper using a different method. Moreover, we prove in particular examples of pp-waves that all Killing tensors of degree 3 and 4 are reducible. We then study the Wils metric, another subclass of the Koutras-McIntosh spacetimes. This metric has a univariate function as its parameter. By using Cartan's prolongation method we deduce the explicit form of the function for which the Wils metric admits a Killing vector, and for which a Killing 2-tensor. This existence result for a Killing vector makes a statement by Koutras and McIntosh more precise. Finally, we show in particular examples of a Wils metric that all Killing 3- and 4-tensors are reducible

STR-833: EVALUATION OF THE CONTRIBUTION OF PANEL ZONES TO THE GLOBAL PERFORMANCE OF MOMENT RESISTING FRAMES UNDER SEISMIC LOAD

Before the 1994 Northridge Earthquake, the seismic design strategy for moment resisting frames considered the yielding of the panel zone when calculating the required level of ductility. Following the unacceptable performance of conventional moment resisting frame (MRF) connection details during the Northridge seismic event, prequalified connections were developed to concentrate beam yielding away from the column face, preserving the connection. With these new connection strategies, the panel zone deformation may not contribute as significantly to the overall behaviour of an MRF. Therefore, considering the increased use of advanced dynamic modeling techniques, it is important for both designers and researchers to know what level of modelling detail is required to properly capture the behaviour of an MRF. This paper examines the influence of the panel zone model on the global performance of a moment resisting frame. The nine-storey SAC building is used as a model to evaluate the influence of this variation. The beam-to-column connections use reduced beam sections and are modeled with OpenSees using nonlinear elements that that capture cyclic deterioration. In one case, the panel zones are modelled as rigid offsets with no shear yielding. In the other case, the panel zones are modeled using a rotational spring box, in which rigid links are arranged in a rectangle and connected at the four corners by three pins and one nonlinear spring that captures the shear distortion in the panel zone. An Incremental Dynamic Analysis with 7 ground motions is conducted to determine the differences in global performance. The more refined panel zone model results in a longer first mode period and less energy dissipation in the plastic hinges of the beams. However, the difference in engineering demand parameters at design level events is minimal and may not justify the increase in computational requirements unless collapse assessment is desired

Iminoboronates as Dual-Purpose Linkers in Chemical Probe Development

Chemical probes that covalently modify proteins of interest are powerful tools for the research of biological processes. Important in the design of a probe is the choice of reactive group that forms the covalent bond, as it decides the success of a probe. However, choosing the right reactive group is not a simple feat and methodologies for expedient screening of different groups are needed. We herein report a modular approach that allows easy coupling of a reactive group to a ligand. α-Nucleophile ligands are combined with 2-formylphenylboronic acid derived reactive groups to form iminoboronate probes that selectively label their target proteins. A transimination reaction on the labeled proteins with an α-amino hydrazide provides further modification, for example to introduce a fluorophore.</p

Intensity-modulated radiotherapy of nasopharyngeal carcinoma: a comparative treatment planning study of photons and protons

<p>Abstract</p> <p>Background</p> <p>The aim of this treatment planning study was to investigate the potential advantages of intensity-modulated (IM) proton therapy (IMPT) compared with IM photon therapy (IMRT) in nasopharyngeal carcinoma (NPC).</p> <p>Methods</p> <p>Eight NPC patients were chosen. The dose prescriptions in cobalt Gray equivalent (Gy_E) for gross tumor volumes of the primary tumor (GTV-T), planning target volumes of GTV-T and metastatic (PTV-TN) and elective (PTV-N) lymph node stations were 72.6 Gy_E, 66 Gy_E, and 52.8 Gy_E, respectively. For each patient, nine coplanar fields IMRT with step-and-shoot technique and 3D spot-scanned three coplanar fields IMPT plans were prepared. Both modalities were planned in 33 fractions to be delivered with a simultaneous integrated boost technique. All plans were prepared and optimized by using the research version of the inverse treatment planning system KonRad (DKFZ, Heidelberg).</p> <p>Results</p> <p>Both treatment techniques were equal in terms of averaged mean dose to target volumes. IMPT plans significantly improved the tumor coverage and conformation (<it>P </it>< 0.05) and they reduced the averaged mean dose to several organs at risk (OARs) by a factor of 2–3. The low-to-medium dose volumes (0.33–13.2 Gy_E) were more than doubled by IMRT plans.</p> <p>Conclusion</p> <p>In radiotherapy of NPC patients, three-field IMPT has greater potential than nine-field IMRT with respect to tumor coverage and reduction of the integral dose to OARs and non-specific normal tissues. The practicality of IMPT in NPC deserves further exploration when this technique becomes available on wider clinical scale.</p