Developments of a W-band gyro-TWA for high PRF operation

Latest developments of a gyrotron travelling wave amplifier (gyro-TWA) with a helically corrugated waveguide and a cusp electron gun for operation over a bandwidth of 90-100 GHz at a high pulse repetition rate (5 kHz) are presented. Performance upgrades of the input coupler, pulsed power system and beam collector with water-cooling capability were realized for the high power wide band gyro-TWA

High pulse repetition frequency operation of a W-band Gyro-TWA based on a cusp electron beam source

The components of a W-band gyro-TWA including input coupler, output window, corrugated output mode converter, pulsed power system and water-cooled beam dump are being upgraded to achieve an output power of 5 kW and a high pulse repetition rate of 2 kHz for cloud radar applications. Latest results of the W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented

Latest development of a W-band Gyro-TWA based on a helically corrugated interaction region

Latest development and experimental study of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With an input seed signal from an 1.5 W, 90-96 GHz solid state source a gain of 27 dB was measured from the experiment. The bandwidth of the gyro-TWA was measured to be at least 5 GH

W-band Brewster window for a wideband gyro-TWA

This paper presents the design of a Brewster window for a W-band gyrotron travelling wave amplifier (gyro-TWA). To maintain the Gaussian-like HE11 mode from the corrugated horn, a corrugated waveguide was optimized to host the Brewster window. The Brewster window was simulated and measured to have a lower than -20 dB reflection over the frequency band 85-101 GHz

Measurement of a W-band gyro-TWA experiment based on a helically corrugated interaction region

Measurements of an upgraded W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With upgraded input coupler and output systems a gain of ~37 dB was measured from the experiment with a maximum output power of over 2 kW. The amplification from the gyro-TWA was measured in the frequency range of 90 GHz to 96 GHz

Further experiments of a W-band gyro-TWA based on a helically corrugated interaction region

Latest results of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun for operation at a high pulse repetition rate are presented. Performance upgrades of input coupler, output window, corrugated horn, pulsed power system and beam collector with water-cooling capability were realized. With an input seed signal from an 1.5 W, 90-96 GHz solid state source the amplification gain and minimum bandwidth were measured from the experiment

Synthesis and Quantitative Structure–Activity Relationship of Imidazotetrazine Prodrugs with Activity Independent of O6-Methylguanine-DNA-methyltransferase, DNA Mismatch Repair and p53.

The antitumor prodrug Temozolomide is compromised by its dependence for activity on DNA mismatch repair (MMR) and the repair of the chemosensitive DNA lesion, O6-methylguanine (O6-MeG), by O6-methylguanine-DNA-methyltransferase (EC 2.1.1.63, MGMT). Tumor response is also dependent on wild-type p53. Novel 3-(2-anilinoethyl)-substituted imidazotetrazines are reported that have activity independent of MGMT, MMR and p53. This is achieved through a switch of mechanism so that bioactivity derives from imidazotetrazine-generated arylaziridinium ions that principally modify guanine-N7 sites on DNA. Mono- and bi-functional analogs are reported and a quantitative structure-activity relationship (QSAR) study identified the p-tolyl-substituted bi-functional congener as optimized for potency, MGMT-independence and MMR-independence. NCI60 data show the tumor cell response is distinct from other imidazotetrazines and DNA-guanine-N7 active agents such as nitrogen mustards and cisplatin. The new imidazotetrazine compounds are promising agents for further development and their improved in vitro activity validates the principles on which they were designed

Global population divergence and admixture of the brown rat (Rattus norvegicus)

Native to China and Mongolia, the brown rat (Rattus norvegicus) now enjoys a worldwide distribution. While black rats and the house mouse tracked the regional development of human agricultural settlements, brown rats did not appear in Europe until the 1500s, suggesting their range expansion was a response to relatively recent increases in global trade. We inferred the global phylogeography of brown rats using 32 k SNPs, and detected 13 evolutionary clusters within five expansion routes. One cluster arose following a southward expansion into Southeast Asia. Three additional clusters arose from two independent eastward expansions: one expansion from Russia to the Aleutian Archipelago, and a second to western North America. Westward expansion resulted in the colonization of Europe from which subsequent rapid colonization of Africa, the Americas and Australasia occurred, and multiple evolutionary clusters were detected. An astonishing degree of fine-grained clustering between and within sampling sites underscored the extent to which urban heterogeneity shaped genetic structure of commensal rodents. Surprisingly, few individuals were recent migrants, suggesting that recruitment into established populations is limited. Understanding the global population structure of R. norvegicus offers novel perspectives on the forces driving the spread of zoonotic disease, and aids in development of rat eradication programmes

Phytase activity in lichens

Phytase activity was investigated in 13 lichen species using a novel assay method. The work tested the hypothesis that phytase is a component of the suite of surface-bound lichen enzymes that hydrolyse simple organic forms of phosphorus (P) and nitrogen (N) deposited onto the thallus surface. Hydrolysis of inositol hexaphosphate (InsP6, the substrate for phytase) and appearance of lower-order inositol phosphates (InsP5–InsP1), the hydrolysis products, were measured by ion chromatography. Phytase activity in Evernia prunastri was compared among locations with contrasting rates of N deposition. Phytase activity was readily measurable in epiphytic lichens (e.g. 11.3 lmol InsP6 hydrolysed g-1 h-1 in Bryoria fuscescens) but low in two terricolous species tested (Cladonia portentosa and Peltigera membranacea). Phytase and phosphomonoesterase activities were positively correlated amongst species. In E. prunastri both enzyme activities were promoted by N enrichment and phytase activity was readily released into thallus washings. InsP6 was not detected in tree canopy throughfall but was present in pollen leachate. Capacity to hydrolyse InsP6 appears widespread amongst lichens potentially promoting P capture from atmospheric deposits and plant leachates, and P cycling in forest canopies. The enzyme assay used here might find wider application in studies on plant root–fungal–soil systems