Quansi-optical mode converter for Ka-band application on a gyrotron

A series of electron cyclotron masers (ECMs) has been designed and successfully operated in the frequency range of 6 to 200 GHz over the past 10 years at Strathclyde University. The current Mk. VI ECM operated between 35–200 GHz, the TE _{0 1} ⁰ mode (35.2 GHz) being the lowest order cavity mode excited. Investigation of this ECM and quasi-optical converter combination was made to establish to what extent a Gaussian beam could be produced from the TE _{0 1} ⁰ gyrotron cavity mode. An antenna of the Vlasov (step-cut radiator) configuration was chosen and successfully developed in a series of low-power experiments up to the W-band frequency regime. The low-power experiments demonstrated that such an antenna system could be constructed and operated in the K_a-band frequency region without resorting to high precision quasi-optical components. The final version of the quasi-optical antenna was externally coupled to the output window of the maser and a plane polarized pencil beam was successfully obtained from the combined maser/Vlasov antenna mode converter. A theoretical model involving a single TE _0n ⁰ input mode was chosen to analyse the output beam characteristics from the Vlasov antenna system. Comparison was made between the single mode theoretical model and the experimental results obtained from the maser.     

Crystallization phenomena in some polyester — urethanes

A density balance has been used to measure the crystallization isotherms of poly(ethylene adipate) and copolymers which were prepared by extending the polyester with four different diisocyanates. The occurrence of extensive secondary crystallization processes precluded satisfactory interpretation in terms of the Avrami theory and further analysis could only be based on the half-time for crystallization. This parameter has the advantage that it is determined directly and is independent of any theoretical analysis. The presence of very small concentrations of diisocyanate units can have a profound effect on the rate of crystallization if they are very different structurally from the parent polyester, e.g. a molar concentration of about 5% of 2,4-tolylene diisocyanate increases the half-time by a factor of 20 whereas the same concentration of hexamethylene diisocyanate has an insignificant effect. The temperature dependence of the half-times is discussed in relation to several theories of crystallization.     

Renal trauma and hypertension: the role of renin

Three patients developed hypertension following renal trauma. Trauma produced perinephric hematoma in two and renal artery thrombosis in one. Renal vein plasma renin activity (PRA) from the traumatized kidney was three to eight times greater than renal vein PRA from the untraumatized (contralateral) kidney. Peripheral PRA was elevated in all. A surgical operation lowered peripheral PRA to normal in all, but corrected hypertension in only two of three. Preoperative medical treatment with renin-suppressing pharmacologic agents correctly predicted this response to surgery. Postoperative renal vein PRA in the remaining hypertensive patient demonstrated that surgery successfully alleviated the abnormality in renin secretion. These studies suggest that excessive renin secretion initiate but other unidentified factors may contribute to the hypertension observed after renal trauma.     

Effect of alum treatment on the trihalomethane formation and bacterial regrowth potential of natural and synthetic waters

Waters from five reservoirs and "synthetic waters", prepared using terrestrially derived dissolved organic matter (DOM) extracted from vegetation and reservoir catchment soils, were studied for their treatability with alum using a jar test procedure. DOM in drinking water is a precursor for the formation of trihalomethanes (THM) following chlorine disinfection and can also be a substrate for microbial growth in the drinking water distribution system. The trihalomethane formation potential (THMFP) represents an upper concentration limit on THMs formed by chlorination, while bacterial regrowth potential (BRP) is an indicator of the bioavailability of DOM. BRP and THMFP were measured before and after alum treatment and the results were related to the source of the DOM. It was found that freshly derived terrestrial DOM in synthetic water resulted in higher THMFP and BRP than DOM in reservoir waters. For the samples investigated, conventional alum treatment did not always reduce the THM precursor levels formed in laboratory tests below the NH&MRC (1996) guideline level of 250 microg/L nor produce microbially stable waters.     

Effect of soil composition and dissolved organic matter on pesticide sorption

The effect of the solid and dissolved organic matter fractions, mineral composition and ionic strength of the soil solution on the sorption behaviour of pesticides were studied. A number of soils, chosen so as to have different clay mineral and organic carbon content, were used to study the sorption of the pesticides atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), 2,4-D ((2,4-dichlorophenoxy)acetic acid), isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) and paraquat (1,1'-dimethyl-4,4'-bipyridinium) in the presence of low and high levels of dissolved organic carbon and different background electrolytes. The sorption behaviour of atrazine, isoproturon and paraquat was dominated by the solid state soil components and the presence of dissolved organic matter had little effect. The sorption of 2,4-D was slightly affected by the soluble organic matter in the soil. However, this effect may be due to competition for adsorption sites between the pesticide and the soluble organic matter rather than due to a positive interaction between the pesticide and the soluble fraction of soil organic matter. It is concluded that the major factor governing the sorption of these pesticides is the solid state organic fraction with the clay mineral content also making a significant contribution. The dissolved organic carbon fraction of the total organic carbon in the soil and the ionic strength of the soil solution appear to have little or no effect on the sorption/transport characteristics of these pesticides over the range of concentrations studied.     

Filiform polyposis of the colon. First report in a case of transmural colitis (Crohn's disease)

Filiform polyposis of the colon is characterized by multitudinous wormlike projections of mucosa and submucosa, and it has only previously been reported to be an unusual sequel to a prior limited episode of ulcerative colitis. The first reported instance complicating a 16-year course of typical transmural colitis (Crohn's disease) suggests that this benign proliferation may be a nonspecific submucosal response to two separated, but closely subadjacent zones of submucosal inflammation in either type of colitis. Although few cases of filiform polyposis are available for review, there has been no instance associated with carcinoma. The entity in itself does not represent an indication for colectomy.     

The fatty acid composition of the lipids from two species of hake

The fatty acid composition of lipids extracted from the livers, muscle and skin of two hake species Merluccius capensis and M. paradoxus were studied. In one instance a comparison was made between the fatty acid composition of the phospholipid and triglyceride fractions of the lipids. In pre-spawning fish there appears to be a tendency for M. capensis to have fat of higher unsaturation than M. paradoxus. The only consistent species difference found was the high level of unsaturation of skin lipids relative to muscle lipids in M. paradoxus, a species living at greater depth and lower water temperatures. The major saturated fatty acid in hake lipids is that with 16 carbon atoms, the major monoenoic acid the one with 18 carbon atoms, while C_22:6 is the dominant polyenoic fatty acid and C_20:5 the second most plentiful in hake lipids. Phospholipids form a small proportion of the lipid from dark muscle. They are particularly rich in the fatty acids C_16:0 and C_22:6.     

福州五四北泰禾广场

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Megawatt, 330 Hz PRF tunable gyrotron experiments

Repetitively pulsed and cw gyrotrons have hitherto used thermionic cathodes, whereas cold cathode gyrotrons have normally operated as ‘single shot’ devices. The novel results presented here show that cold cathode gyrotrons can be successfully pulsed repetitively. A tunable gyrotron with a pulse repetition frequency (PRF) of 150Hz is demonstrated. This system developed >4MW mm-wave output pulses at 100GHz. The gyrotron is based on a two-electrode configuration comprising a field-immersed, field emission, cold cathode and a shaped anode cavity. A superconducting magnet was used to produce the homogeneous intra-cavity magnetic field and a cable pulser was used to drive the electron beam. This pulser produced up to a (200±20)kV pulse with 10ns rise time, a 100ns flat top, a 10ns decay with a characteristic impedance of 200Ω. The energy storage capacity of the cable pulser was 35J. The charging unit limited the maximum PRF to 330Hz. Due to spark gap switching limitations 330Hz was only obtainable in 5 to 10 pulse bursts. For substantial periods of the order of 30 seconds, 100Hz PRF was achieved over an oscillating range of 28 to 100GHz and 150Hz PRF was achieved at 80GHz. No degradation effects on the mm-wave output pulse was evident due to diode recovery time throughout this series of results. A subsequent conclusion is that the diode recovery time in our cold cathode gyrotron is less than 3ms.