Longer Gap Research Articles

An Iron-Free Magnetron-Injection-Gun for a 28GHz, 200kW Gyroklystron Amplifier

A design study of a double-anode magnetron-injection-gun is performed to incorporate the electron gun into a high power 28GHz gyroklystron amplifier operating at 70kV and 8.2A. The electron gun is designed to be used in a tapered magnetic field in the cathode region produced from an iron-free superconducting magnet. An electron trajectory code predicts a beam axial velocity spread of 5.9% at α = 1.5, 70kV, 8.2A and 10.4kG, which is a high quality electron beam suitable for the high gain, high efficiency, five-cavity gyroklystron amplifier. The successful design of the high quality electron gun is attributed to a longer gap between the modulating anode and the grounded anode compared with the case of the first 28GHz electron gun built with an iron enclosed electromagnet.

On the Generation of Antisaccades in Different Conditions

To generate a saccade in the direction opposite to the stimulus site (antisaccade) takes a conscious voluntary effort: first, one needs an intact fixation system to prevent saccades to the stimulus (prosaccades) and second, one has to generate a saccade to a location with no target. While the maintenance of fixation relies on an intact tectum, the correct performance of the antitask relies on an intact frontal system. Valid peripheral precues for attention capture indicating the direction of the antisaccade increase the error rate and the reaction time of the antisaccades. In this study we investigated how different conditions of stimulus presentation influence the performance of the antitask. We varied systematically the duration of the gap (time between fixation point offset and stimulus onset) from zero to 600 ms, and the stimulus eccentricity from 1 to 12 deg. Eye movements were recorded under infrared light. We analysed the reaction time of the correct antisaccades (a-srt) and of the erratic prosaccades (p-srt), and the percentage of errors (%-err) separately for the right and the left stimulus. Increasing the gap to 200 ms increased the %-err by 10% and decreased the a-srt by 30 ms. For longer gap durations these effects disappeared. With larger saccades the p-err rates decreased and the p-srt were reduced by 10 ms mostly staying in the range of express saccades and following the corresponding prosaccades in protasks. The a-srt decreased systematically with increasing eccentricity. The results have implications for voluntary versus involuntary control of saccades and are related to the significance of the antitask in clinical studies.

A Study of Nerve Regeneration Across Synthetic (Maxon) and Biologic (Collagen) Nerve Conduits For Nerve Gaps Up to 5 Cm in the Primate

In a primate model, nerve regeneration was evaluated across 2- and 5-cm nerve gaps using a synthetic nerve conduit (glycolide trimethylene carbonate, Maxon) and a biologic conduit (collagen). Two types of conduits from glycolide trimethylene carbonate (Maxon) were evaluated. The first was fashioned into a tube from a single flat piece of Maxon mesh. The second was prefabricated in a crimped form. The other material evaluated was a biologic collagen tube. At 14 months, excellent regeneration was noted across the 2-cm nerve gap through both the collagen and Maxon conduits. At 5 cm, the regeneration, as determined by morphometric analysis, was significantly better across the Maxon prefabricated, crimped conduit, although regeneration at this longer gap in all experimental groups was significantly less than across the shorter nerve gap. At the longer gap, there was no statistical difference between the groups by electrophysiologic assessment.

Child mortality in a rural Javanese village: a prospective study.

Mortality in the first two years of life was studied in a cohort of 510 children born in a rural Javanese village. Lower risk of death was associated with younger maternal age, maternal schooling, ownership of a well, smaller sibship, longer gap between child and next oldest sibling and, in particular, with good nutritional status. Diarrhoea, pneumonia and immunizable diseases accounted for over half the deaths, with malnutrition contributing to most. A primary health care programme focusing on malnutrition, immunization and early treatment for diarrhoea and pneumonia could reduce mortality by half or more in this population.

Impulse Breakdown of Polymer Dielectrics in the NS Range in Divergent Fields

The short time impulse breakdown of polymer dielectrics, polyethylene (PE), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), and polymethyl methacrylate (PMMA) in a pointplane electrode system has been studied using a ns rise time pulser. A polarity effect was found in all polymers: a highet voltage is required to induce breakdown for a negative point than for a positive point. This effect usually increases with increasing gap distance except for PMMA, in which the ratio of the negative to the positive breakdown voltage is small even for longer gap distances. There is much difference in the results of the 50% breakdown voltage Vb for pulses of 100 ns duration for each polymer. Vb for PS is the very highest among polymers tested in both negative and positve points. Vb for PET and Vb for PMMA are the lowest in the positive point and in the negative point, respectively, in the thicker gap region. The formative time lag is, in most cases, less than about 10 ns.

The Wilkins Lecture, 1973 - Newton and his editors

On 14 September 1669 the Secretary of the Royal Society, Henry Oldenburg, wrote to his correspondent in Liège, René François de Sluse, a brief note on the analytical method of a young Cambridge mathematician, Isaac Newton by name. 1 This note marks Newton’s first appearance before the learned world at large, where in a few years’ time he was to become far better known in the field of optics, and it is interesting that the treatise upon which Oldenburg’s note was ultimately based, the De analysi , was only to be printed forty-two years later when much of its freshness was, inevitably, dimmed; and then not by Newton himself but by his protégé William Jones. As I think is generally known, such a delay in publication of his work was by no means unusual with Newton; Opticks , of which a large part had been communicated to the Royal Society by 1675, was published only in 1704, while the Cambridge optical lectures on which that book was in part based only saw print some sixty years after their delivery, when Newton himself was dead. Only one of Newton’s books, the one with which I am chiefly concerned this afternoon, was written in the actual heat of intellectual discovery. We know that in the summer of 1684 Newton possessed but the barest outline of the future Philosophiae Naturalis Principia Mathematica , if so much; yet by June 1687, less than three years later, the book was in print after the last section of it had been written twice over. Let me review – it will not take long – the story of Newton’s major publications. The Cambridge Varenius of 1672 need not detain us; but for the title-page there is almost nothing of Newton in it. Next a long interval during which, however, Newton’s name appeared frequently in the Philosophical Transactions , until the Principia in 1687; and another even longer gap before Opticks in 1704. Then, in­deed, in Newton’s seventh decade, partly under pressure from the claims and criticisms of Leibniz and his supporters, Newton’s work came frequently before the public; Opticks was reprinted several times in both Latin and English, his early mathematical writings were published by Whiston (in 1707) and Jones (in 1711), and selections from his mathematical correspondence of long before appeared in the Commercium epistolicum of 1712.

Estimation of small effective gap length beyond recording resolution in magnetic data recording systems

A new method is described whereby extremely short effective gap lengths of ring type reproducing heads used in high resolution magnetic recording instruments can be determined. The method is based on comparison of the frequency or wavelength response of the short gap head with that of a second head of longer gap length which can be conveniently measured by the first null-point method reported previously. Experimental results for the measurement of a head gap of the order of 20 × 10−6 in are given as an illustration.

The scientific role: The conditions of its establishment in Eeurope

Introductory Remarks Ancient science failed to develop not because of its immanent shortcomings but because those who did scientific work did not see themselves, nor were they seen by others, as scientists, but primarily as philosophers, medical practitioners, or astrologers. Only this can explain why the appearance of Galileo had to wait for some 1,800 years after Archimedes, or the even longer gap between Aristotle's and Theophrastus' systematisations of living and growing things and those of Linnaeus and Cuvier. Had there existed among the Greeks several generations of intellectuals conceiving of themselves as scientists with the motivations and obligations entailed in that they could undoubtedly have applied themselves to the discovery of a less cumbersome method of mathematical notation and have made many of the scientific advances accomplished in the sixteenth and seventeenth centuries and subsequently. It is true that much of the Greek tradition was lost in the Middle Ages as a result of catastrophes but the stagnation and deterioration of the tradition had started earlier. Furthermore, had there been a group of persons, who inherited the Greek scientific tradition and who regarded themselves as scientists, anywhere in the Christian or the Moslem world or among the Jews, the Greek achievements might have been rediscovered in the Middle Ages or, at any rate, much more efficient use would have been made of them in the

MINIMUM SPARK BREAKDOWN AND GLOW VOLTAGES

Measurements of the spark breakdown voltage between carbon electrodes in hydrogen, argon, nitrogen, and air are given for ranges of the product p (mm. Hg) × d (cm.) between 0.1 and 1000 mm. Hg cm. The results show that in each gas Paschen's Law is obeyed for pd > 10 mm. Hg cm. For pd < 10 mm. Hg cm. deviations from Paschen's Law were observed at the longer gap lengths. The minimum spark breakdown voltage, Vsm, occurred near pd = 1 mm. Hg cm. The normal cathode-fall voltage, Vcn, was also measured, and was found to be less than Vsm in hydrogen, argon, and air, and greater than Vsm in nitrogen. A theoretical analysis is made which predicts the relationship Vcn = 1.110 Vsm and the reasons why this condition is seldom found in practice are discussed.