Helix Type Research Articles

Intramolecular steric effects and hydrogen bonding in regular conformations of polyamino acids.

AbstractA survey has been made, by using computer methods, of the types of helices which polypeptide chains can form, taking into account steric requirements and intramolecular hydrogen‐bonding interactions. The influence on these two requirements, of small variations in the bond angles of the peptide residues, or of small changes in the overall dimensions of the helix (pitch and residues per turn), have been assessed for the special case of the α‐helix. Criteria for the formation of acceptable hydrogen bonds have also been applied to helices of other types, viz., the 3, γ−, ω−, and π‐helices. It was shown that the NH … O and H … OC angles in hydrogen bonds are sensitive to changes in either the NCαC′ bond angle or in the rotational angles about the NCαand CαC′ bonds. However, the variants of the α‐helix observed experimentally in myoglobin can all be constructed without distortion of the hydrogen bonds. For α‐helices, the steric and hydrogen bonding requirements are more easily fulfilled with an NCαC′ bond angle of 111°, rather than 109.5°. The decreased stability observed for the left‐handed α‐helix relative to the right‐handed one forL‐amino acids is due essentially only to interactions of the Cβatom of the side chains with atoms in adjacent peptide units in the backbone, and interactions with atoms in adjacent turns of the helical backbone are not significantly different in the two helices. Restrictions in the freedom of rotation of bulky side chains may have significant kinetic effects during the formation of the α‐helix from the “random coil” state.

螺線型表面波線路からの漏洩電界

螺線型表面波線路からの漏洩電界

Broadband Oscilloscope Tube

By applying traveling wave tube principles to the design of a helix type vertical deflection system it has become possible to build an oscilloscope tube whose bandwidth characteristic is flat over 600 megacycles. The trace on the fluorescent screen is readable without other optical means. The tube construction is similar to commercial cathode ray tubes, the only exception being that the alignment of the various tube elements has a closer tolerance. In actual use this tube allows one to view directly repetitive pulses a few millimicroseconds in width.

An experimental investigation of cavity-mounted helical antennas

This paper presents the results of an experimental investigation which led to the development of cavity-mounted helical antennas for airborne applications. The effects on patterns and impedance of various antenna parameters, such as number of turns, cavity size and shape, helix pitch, angle, and conductor size, were investigated. Methods of feeding the helix which produce an input impedance near 50 ohms, without external compensation, throughout the axial mode frequency range are discussed. Some of the types of cavity-mounted helices developed and typical performance data are described.

Large signal behavior of high power traveling-wave amplifiers

The results of an experimental investigation on the large signal behavior of a kilowatt power level helix type traveling-wave amplifier tube are presented. Operation with and without attenuators was investigated using a movable electromagnetic probe to measure power level along the tube. Quite different effects of drive power and beam voltage on the saturation level were found for operation with and without attenuators. The maximum power level is lower for attenuator operation. Also, power levels do not continue to increase with increasing beam voltage and drive power. In contrast, attenuator-less operation produces the highest efficiency, and the power levels continue to rise with increasing beam voltage and drive power. Conversion efficiencies as high as 25 per cent are obtained with an attenuator and as high as 40 per cent without an attenuator. Efficiency calculations based on small-signal theory can be made to agree reasonably well with the experimental attenuator-less operation efficiencies by assuming an appropriate ratio of the ac component of beam current to the dc component of beam current, i/I 0 .