Universiẗat, Diss., 2002--Frankfurt (Main).

A new variation of the spherical helical antenna made of a wire wound over a hemispherical surface and backed by a conducting ground plane is introduced. A constant spacing is maintained between the turns of winding. The geometry of this antenna is fully described by the number of turns and the radius of hemispherical surface. In addition to the hemispherical geometry, truncated double spherical helices are also examined. Radiation properties of the proposed antennas are studied both theoretically and experimentally. The wire antenna code ESP (electromagnetic surface patch), which is based on the method of moments, is used to obtain simulation results. The results for far-field patterns, gain, axial ratio, bandwidth, and input impedance are presented. Several prototypes of this antenna were constructed and tested using an outdoor antenna range. Far-field patterns were measured over a wide range of frequencies. The measured and calculated radiation patterns are in good agreement. A unique property of the hemispherical helix is its broad half-power beamwidth. Furthermore, this antenna provides circular polarization and relatively high gain over a narrow frequency range. The results of this research show that, for example, a 4.5-turn hemispherical helix with a radius of 0.02 meter designed for operation around 2.8 GHz provides a half-power beamwidth of about 90 degrees, more than 9 dB gain, and less than 3 dB axial ratio over a 300 MHz bandwidth. The input impedance of the antenna is largely resistive and is about 150 ohms in the above frequency range. Compared with a full spherical helix, the hemispherical helix provides comparable radiation characteristics, but occupies only half the volume. The compact size of this antenna makes it attractive to mobile communication applications / Master of Science

No description available.

No description available.

A unique property of spherical and hemispherical helical antennas is that they provide very broad half-power beamwdiths and circular polarization over a narrow bandwidth. In this thesis, new designs for hemispherical helical antennas are introduced that provide significant improvement in bandwidth, while maintaining the directivity and half-power beamwidth of the basic design. In the basic design, a simple wire of circular cross section is wound on the surface of a hemisphere, whereas in the proposed new designs a metallic strip forms the radiating element. Furthermore, the metallic strip may be tapered and tilted relative to the hemispherical surface, allowing wider bandwidth to be achieved. The antenna is fed by a coaxial cable with the inner conductor connected, through a matching section, to the radiating strip and its outer conductor connected to a ground plane. Radiation properties of the proposed hemispherical helical antennas are studied both theoretically and experimentally. A commercial software, based on the method of moments, is used to perform the numerical analysis of these helices. Three-dimensional far-field patterns, axial ratio, directivity, and voltage standing-wave ratio (VSWR) are calculated for several designs. The impacts of tapering as well as tilting of the metallic strip on radiation characteristics are examined. Also, matching of the proposed hemispherical antennas to 50â ¦ transmission lines is addressed. A 4.5-turn hemispherical helix with tapered radiating element and zero degree tilt angle, (metallic strip is perpendicular to the hemisphere axis of symmetry) provides the largest overall bandwidth. A nonlinearly tapered matching section is incorporated into the design in order to reduce the VSWR. For this design, an overall measured bandwidth of about 24% at a center frequency of 3.35 GHz is achieved. Over this bandwidth, the axial ratio remains below 3 dB, the VSWR is less than 2, and the directivity is about 9 ±1 dB. A half- power beamwidth of 70° is also obtained. A prototype of the best design was fabricated and tested using the VT indoor antenna range. Radiation patterns, the scattering parameter S₁₁, and the axial ratio were measured. The measured and simulated results agree reasonably well. In particular, agreements between measured and calculated far-field patterns and VSWR are quite remarkable. This compact, low profile antenna might find useful applications in avionics, global positioning systems (GPS), and high data rate wireless communication systems. / Master of Science

published_or_final_version / abstract / Pathology / Doctoral / Doctor of Philosophy

<p>Programmed cell death, or apoptosis, has during the last decade received a lot of attention due to its involvement in a large number of pathological conditions. Since death is always irreversible, it is important for cells to fully control the initiation and execution of this process. One of many apoptosis-regulatory proteins is XIAP, which blocks the action of caspases, a family of proteases that are important during apoptosis. However, apoptosis inhibitors have to be tightly controlled since too little cell death can lead to the development of tumors and other diseases. This thesis is the result of an aspiration to fully understand the function and regulation of XIAP.</p><p>By using the yeast-2-hybrid system, we identified two novel binding partners of XIAP. The first, GPS2, was found to bind XIAP and inhibit its ability to block caspase-activity. In addition, GPS2 induced caspase-mediated cell death in two different tumour cell lines and XIAP inhibited this effect.</p><p>The second binding partner, Nulp1, preferentially bound XIAP in the presence of the apoptosis-inducer staurosporine. Nulp1 induced or sensitized cell lines to cell death when overexpressed, but this was not blocked by caspase-inhibitors or XIAP, suggesting a different reason for binding than apoptosis regulation. With the aim to understand the Nulp1-XIAP interaction, we continued to study Nulp1 <i>in vivo</i> and <i>in vitro</i>. We studied three different splice variants of Nulp1 and found that they were regulated by poly-ubiquitination and nuclear shuttling. Also, Nulp1 was expressed in embryonic mice, especially in the cortical plate, hippocampal neurons and cerebellar granular neurons. Expression of Nulp1 decreased with age but was still present in cerebellar deep nuclei and Purkinje cells of adult mice. </p><p>To summarize, we have identified GPS2 as an apoptosis-inducing factor and an inhibitor of XIAP <i>in vitro</i>, and Nulp1 as a XIAP-interacting protein during staurosporine-induced apoptosis.</p>

In der vorliegenden Arbeit werden Ergebnisse vom Experiment HERMES präsentiert, welche eine azimutale Asymmetrie bezüglich des Spins des Protontargets zeigen, die von der Interferenz zwischen dem Bethe-Heitler und dem Tiefvirtuelle Compton Streuung (DVCS) Prozess herrührt. Diese Asymmetrie, auch als longitudinale Target-Spin Asymmetrie (LTSA) bezeichnet, erlaubt hauptsächlich den Zugang zur polarisierten verallgemeinerten Partonverteilungen (GPD) H-tilde. Die kinematische Abhängigkeit der LTSA von t, x_B und Q2 wurde gemessen und mit vorhandenen Messungen am Deuteron verglichen. Die Ergebnisse wurden mit theoretischen Berechungen und mit aktuellen Messungen des CLAS-Experiments verglichen. Die Daten, die zur Analyse in der vorliegenden Arbeit verwendet werden, wurden am HERMES Experiment bei DESY genommen, wobei im HERA-Speicherring Positronenstrahlen der Energie 27.5 GeV an Wasserstoff- und Deuterium-Gas-Targets gestreut wurden. Darüber hinaus werden Produktionstests des HELIX-128 3.0 chips diskutiert. Der Chip ist ein Frontend-Auslesechip beim Silizium-Rückstossdetektor. Letzterer ist Teil des HERMES-Rückstossdetektors, welcher den Target-Bereich umschliesst, um die Rückstossprodukte der exklusiven Prozesse zu detektieren. Das primäre Ziel dieses Detektors ist es, eine vollständigere Untersuchung von DVCS durch zusätzliche Registrierung der Rückstossprotonen zu ermöglichen. / In this thesis results from HERMES are reported on an azimuthal asymmetry with respect to the spin of the proton target, which is attributed to the interference between the Bethe-Heitler process and the Deeply Virtual Compton Scattering process. The asymmetry, also referred to as the longitudinal target-spin asymmetry (LTSA), gives access mainly to the polarized Generalized Parton Distribution H-tilde. The kinematic dependences of the LTSA on t, x_B and Q^2 are measured and compared with the corresponding measurements on the deuteron. The results are compared with theoretical calculations and with the recent CLAS measurements. The data, used for analysis in this thesis, have been accumulated by the HERMES experiment at DESY scattering the HERA 27.6 GeV positron beam off hydrogen and deuterium gas targets. Additionally, production tests of the HELIX128 3.0 chip are discussed. The chip is the frontend readout chip of the silicon recoil detector. The latter is a part of the HERMES recoil detector, which is built around the target area in order to detect the recoiling products of exclusive processes. The primary goal of this detector is to facilitate a more complete study of DVCS by registering also the recoiling protons.

Thesis (Ph. D. in Biological Sciences)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Programmed cell death, or apoptosis, has during the last decade received a lot of attention due to its involvement in a large number of pathological conditions. Since death is always irreversible, it is important for cells to fully control the initiation and execution of this process. One of many apoptosis-regulatory proteins is XIAP, which blocks the action of caspases, a family of proteases that are important during apoptosis. However, apoptosis inhibitors have to be tightly controlled since too little cell death can lead to the development of tumors and other diseases. This thesis is the result of an aspiration to fully understand the function and regulation of XIAP. By using the yeast-2-hybrid system, we identified two novel binding partners of XIAP. The first, GPS2, was found to bind XIAP and inhibit its ability to block caspase-activity. In addition, GPS2 induced caspase-mediated cell death in two different tumour cell lines and XIAP inhibited this effect. The second binding partner, Nulp1, preferentially bound XIAP in the presence of the apoptosis-inducer staurosporine. Nulp1 induced or sensitized cell lines to cell death when overexpressed, but this was not blocked by caspase-inhibitors or XIAP, suggesting a different reason for binding than apoptosis regulation. With the aim to understand the Nulp1-XIAP interaction, we continued to study Nulp1 in vivo and in vitro. We studied three different splice variants of Nulp1 and found that they were regulated by poly-ubiquitination and nuclear shuttling. Also, Nulp1 was expressed in embryonic mice, especially in the cortical plate, hippocampal neurons and cerebellar granular neurons. Expression of Nulp1 decreased with age but was still present in cerebellar deep nuclei and Purkinje cells of adult mice. To summarize, we have identified GPS2 as an apoptosis-inducing factor and an inhibitor of XIAP in vitro, and Nulp1 as a XIAP-interacting protein during staurosporine-induced apoptosis.