Detailed investigations on double confocal waveguide for a gyro-TWT

The error free repair of DNA double strand breaks through the homologous recombinational repair pathway is essential for organisms of all types to sustain life. A detailed structural and mechanistic understanding of this pathway has been the target of intense study since the identification of bacterial recA , the gene whose product is responsible for the catalysis of DNA strand exchange, in 1965. The work presented here began with defining residues that are important for the assembly and stability of the RecA filament, and progressed to the identification of residues critical for the transfer of ATP-mediated allosteric information between subunits in the protein's helical filament structure. My work then evolved to investigate similar mechanistic details concerning the role of ATP in the human RecA homolog, Rad51. Results from non-conservative mutagenesis studies of the N-terminal region of one subunit and the corresponding interacting surface on the neighboring subunit within the RecA protein, led to the identification of residues critical for the formation of the inactive RecA filament but not the active nucleoprotein filament. Through the use of specifically engineered cysteine substitutions we observed an ATP-induced change in the efficiency of cross subunit disulfide bond formation and concluded that the position of residues in this region as defined by the current crystal structure may not accurately reflect the active form of the protein. These ATP induced changes in positioning led to the further investigation of the allosteric mechanism resulting in the identification of residue Phe217 as the key mediator for ATP-induced information transfer from one subunit to the next. In transitioning to investigate homologous mechanisms in the human pathway I designed a system whereby we can now analyze mutant human proteins in human cells. This was accomplished through the use of RNA interference, fluorescent transgenes, confocal microscopy and measurements of DNA repair. In the process of establishing the system, I made the first reported observation of the cellular localization of one of the Rad51 paralogs, Xrcc3, before and after DNA damage. In addition we found that a damage induced reorganization of the protein does not require the presence of Rad51 and the localization to DNA breaks occurs within 10 minutes. In efforts to characterize the role of ATP in human Rad51 mediated homologous repair of double strand breaks we analyzed two mutations in Rad51 specifically affecting ATP hydrolysis, K133A and K133R. Data presented here suggests that, in the case of human cells, ATP hydrolysis and therefore binding, by Rad51 is essential for successful repair of induced damage.

Structured luminescent solar energy concentrators : a new route towards inexpensive photovoltaic energy

High brightness fiber coupling laser module with multi-linear-laser-diode-arrays is designed and fabricated.The laser diode chips are fabricated with a broad waveguide and double quantum well structure by molecular beam epitaxy method.The module contains 6 collimated single linear-laser-diode-arrays which can operate to CW 50 W output power with single emission width of 100 μm,pitch of 500 μm,cavity length of 1 200 μm and 19 emitters per bar.Beam output with high beam quality is obtained by space beam combination and beam shaping afterwards,the combined 6-beam output is focused into a 400 μm-core quartz fiber with NA0.22 by a set of flat-convex cylindrical lens.Finally,a maximum fiber end output power of 195 W with power density of 1.55×105 W/cm2 is achieved,and the total coupling efficiency is as high as 65%.

In this paper a novel structure of metamaterial is proposed in order to miniaturize a rectangular microstrip patch antenna. The metamaterial is composed of two nested split octagons which are located on a 10 mmx10 mm Rogers RT/duroid 5880 with 0.7874 mm thickness and dielectric constant of 2.2. A 3X5 array of such metamaterials is placed on the patch antenna substrate. By using this metamaterial in the antenna structure, the dimension of this proposed antenna is reduced compared to a simple microstrip patch antenna. Simulation results for return loss and radiation pattern of both proposed and conventional antenna are shown and compared. I. Introduction The basic geometry of a microstrip patch antenna(MPA) consists of a metallic patch printed on a grounded substrate. Three commonly used feeding methods are coaxial feed, stripline feed, and aperture- coupled feed. The patch antenna idea was first proposed in the early 1950s, but it was not until the late 1970s that this type of antenna attracted serious attention of the antenna community. The microstrip patch antenna offers the advantages of low profile, conformability to a shaped surface, ease of fabrication, and compatibility with integrated circuit technology, but the basic geometry suffers from narrow bandwidth. Metamaterials are artificial structures, and their electromagnetic properties dont exist in nature. Employing metamaterials in microstrip antenna substrate will result in the improvement of the antenna parameters like bandwidth, gain, efficiency, etc. Additionally, it is possible to miniaturize the antenna as much as desired with these structures, without dealing with surface waves problems. To date, many different techniques have been proposed, based on the use of metamaterials. Applications of double negative (DNG) and single negative (SNG) metamaterials have been widely studied by some research groups in miniaturization of subwavelength cavities, waveguides , and antennas. (6)This project present the possibility of miniaturization of a rectangular microstrip patch antenna by using a novel structure of metamaterial, which is placed on the substrate(1). With the advent and popularity of many wireless services, a quandary has arisen in the antenna community about how to develop small antennas that can satisfy the performance requirements for these systems as well as be aesthetically pleasing to the user. It is interesting to note that the latter point is not insignificant. As with the computer industry, mobile communications is very much a customer-driven market and thus the user requests, although technically with little merit, must be addressed. Ideally, an antenna that is unobtrusive and low cost, and can be located within thecasing of the handset would ensure the compactness of the handset terminal and therefore please the users. Microstrip antennas would appear to be possible candidates because of several attractive features, including their low profile, light weight, and ease of fabrication. Unfortunately, most present-day mobile communication systems are in the lower microwave region of the spectrum (less than 3 GHz) where these antennas in their conventional form are too large for wireless communication handsets. Several approaches have been reported to effectively reduce the size of the printed conductor of a microstrip patch antenna,here a new concept,that is the presence of metamaterial is used.(2) In this paper, we present the possibility of miniaturization of a rectangular microstrip patch antenna by using a novel structure of metamaterial, which is placed on the substrate.(3) First of all, designed a conventional rectangular patch antenna and analysed it. Then the resonance structure of the metamaterial is investigated and analyzed. Then the antenna structure at the presence of this metamaterial in the substrate is investigated and the return loss and radiation pattern of the proposed antenna is compared with the conventional patch antenna with the same dimension.(10)

We are presenting data about the co-localization of Zbtb20 and Sox2 during gestation week 20 in the germinative zones of a human fetal telencephalon. We investigated the ventricular (VZ), internal and external subventricular zones (iSVZ and oSVZ) in the frontal lobe by immunofluorescence confocal microscopy. We determined the pro­portion of double positive cells to all Zbtb20+ cells and compared it to different zones. The analysis demonstrat­ed statistically significant difference between VZ and oSVZ. In oSVZ, we identified populations of Zbtb20+ cells different than Sox2 expressing radial glial progenitors.

Terahertz(THz) imaging technology provides perspective applications in non-destructive inspection, medical diagnostic and national defense. An integrated terahertz confocal imaging system based on THz waveguides was reported in this paper. Firstly, a reflective THz imaging of a metal razor blade with lateral resolution close to wavelength (3 mm) was acquired. Then, a reinforcing metallic bar in concrete was detected effectively, which provided a feasible method to ensure the quality of construction. Further, by introducing a pinhole before the THz detector, a THz confocal imaging system was set up and depth information(24 mm) between two nails inserted in different depths in insulating foam could be extracted, which was three-dimensional information. The results show that the proposed terahertz confocal imaging system based on waveguides structure has the advantages of compact structure and portable integration, which is especially suitable for practical engineering applications.

Quasi-optical confocal cylindrical waveguide possesses a lot of good characteristics, such as big power capacity and low mode density, which can suppress the mode competition in beam-wave interaction. So quasi-optical waveguide has a great advantage in designing high harmonic terahertz gyrotrons. For the reason that part of electron beams located in a region of weak field intensity play a limited role in beam-wave interactions, the beam-wave interaction is not efficient in confocal cavity. Motivated by enhancing the beam-wave interaction efficiency of quasi-optical gyrotron, we propose a novel terahertz harmonic gyrotron cavity with double confocal waveguide in this paper. The transverse field distribution and the mode spectrum in double confocal waveguide are analyzed and presented. A 330 GHz second harmonic gyrotron with double confocal cavity is designed, theoretically analyzed and simulated by using a particle-in-cell (PIC) code. The results obtained for double confocal cavity are compared with the results for single confocal cavity, and the physical mechanism of beam-wave interaction enhancement in double confocal cavity is discussed. Theoretical results show that the double confocal cavity is able to increase the coupling strength of beam-wave interaction, thus, to improve the output power and the interaction efficiency of quasi-optical gyrotron. The PIC simulation results suggest that a high-order waveguide mode in double confocal cavity can steadily interact with the high harmonic cyclotron mode of electron beam without mode competition. Driven by a 40 kV, 2 A electron beam with a guiding center radius of 1.65 mm and velocity ratio equal to 1.5, output power of 9.9 kW at 328.93 GHz can be generated in the designed double confocal cavity. The beam-wave interaction efficiency increases from 5.3% in single confocal cavity to 12.4% in dual confocal cavity under the same operation parameters. The double confocal cavity has great potential applications in terahertz band. Moreover, this study indicates that the eigen mode in double confocal waveguide is a kind of hybrid mode superimposed by two independent single confocal waveguide modes. This mode characteristic will be beneficial to designing a multifrequency gyrotron oscillator operated in two modes and two cyclotron harmonics, simultaneously, with a single electron beam used, which provides a new possibility to develop the novel terahertz radiation source.

Code: A novel MOVPE technique for the single stage growth of buried ridge double heterostructure lasers and waveguides

Confocal cylindrical waveguide performs many good characters, such as big power capacity and low mode density, which are good for designing high harmonic terahertz gyrotron. Motivated by improving beam-wave interaction efficiency of quasi-optical gyrotron, a novel gyrotron beam-wave interaction structure based on double confocal waveguide has been proposed and theoretically analyzed in this paper. A 0.33 THz second harmonic gyrotron oscillator based on double confocal cavity has been designed and simulated by PIC code. It is indicated that double confocal cavity is able to enhance the output power and the interaction efficiency of quasi-optical gyrotron. Besides, the mode characteristic of double confocal waveguide is investigated with the simulation results.

Evaluation of the properties of hydrogenated InP/InGaAsP double heterostructure waveguides

The theory analysis and particle-in-cell (PIC) simulation results of a 140-GHz double confocal waveguide gyrotron traveling-wave amplifier (gyro-TWA) are presented. The mode density in a double confocal waveguide is relatively sparse, and its intrinsic diffraction loss can be against the parasitic oscillation. A high-performance input coupler is designed, and simulation results show that a wave is efficiently converted from TE01 rectangular waveguide mode into the antiphase superposition TE06 double confocal waveguide mode. From theoretical analysis and PIC simulation, when the double confocal gyro-TWA and single confocal gyro-TWA operate under the same parameters, the interaction efficiency of double confocal gyro-TWA is significantly higher than the single confocal gyro-TWA. The calculated results from the nonlinear theory agree well with those from PIC simulation. The performance of the double confocal gyro-TWA is much better than that in the single confocal gyro-TWA due to a more uniform field distribution in the double confocal gyro-TWA.

A quasi-optical interaction structure called a double confocal waveguide has been investigated in details. Previous studies show that the beam-wave interaction efficiency in a double confocal structure is twice as much as that in a conventional quasi-optical structure (single confocal structure). The electro-magnetic characteristics of a double confocal waveguide is presented in this paper.