In submarines, machinery with reciprocating rotating parts is placed on rubber mountings to isolate noise and vibration from the hull of the vessel. Otherwise the hull would radiate the noise to the sea and facilitate detection of the submarine by the enemy. The dynamic mechanical properties of the rubber in the mountings determine to a large extent their effectiveness in isolating noise and vibration. Only within the last ten years has reliable information become available on the dynamic mechanical properties of rubber at high frequencies of vibration. Most of this advance has been due to Nolle. Other workers in this field have been Witte, Mrowca and Guth, Hillier, Cramer and Silver, and Morris, James and Snyder. Nolle gave an excellent description and analysis of techniques for measuring the dynamic mechanical properties of rubber in the frequency range of 0.1 to 120,000 cycles per second (cps). The methods which he described were identified as rocking-beam oscillator, vibrating reed, strip transmission, strip resonance, and magnetostriction. Guth and associates, Hillier, and Cramer and Silver used the strip transmission method in their respective investigations. Morris, James, and Snyder used a bar transmission method which had not been previously described. This paper deals with a modification of the bar transmission method, whereby the resonant frequency and dispersion of the vibrational energy above and below the resonant frequency are measured. From this information the velocity of sound, Young's modulus, and loss factor of the rubber are calculated.

Additional studies covering this point are planned, together with studies to determine whether results similar to those reported here are obtained when other sources of chlorine are utilized, such as chlorinated alkyd resins, vinyl resins, or chlorinated rubber. CONCLUSIONSBy the use of a thermoelectric tester, based on the principle of transformation of electrical energy into heat energy by short. circuiting, across the test specimen, the current delivered by a motor generator, it was possible to evaluate the role of pigment volume, antimony oxide, and chlorinated pariffins in fire-retardant paints.Both antimony oxide and organically combined chlorine are of value as agents to impart fire retapdance.Antimony oxide, used as the sole fire retardant, is effective only when the amount of organic matter in the dry film is smallthat is, only at pigment volumes of 50% or more.The amount of organically combined chlorine necessary to achieve fire retardance depends on the amount of organic matter in the dry film and, t o a lesser extent, on the concurrent presence RECBIVED July 10, 1947.

The authors conclude, from the work reported herein, that commercially available deresinated guayule rubber may best be compounded in the same manner as Hevea rubber, with an expectation of obtaining approximately 75 per cent of the tensile strength of a similar Hevea stock. It is concluded further that deresinated guayule rubber may generally be processed and cured in the same manner as Hevea rubber without sacrificing quality to a greater extent than is done with Hevea rubber.

Recently Werkenthin, Richardson, Thornley and Morris reported on the sunlight and accelerated light aging of various natural and synthetic rubber stocks, and proposed a method for standardizing the accelerated light aging test. The purpose of the present paper is to provide data on the correlation of sunlight aging with accelerated light aging for various synthetic rubber stocks loaded with mineral pigments. FORMULAS AND CURES The formulas and cures for the synthetic rubber stocks are given in Table I. These stocks have a loading corresponding to a good quality, 40 per cent wire insulation compound. Most of the prominent types of synthetic rubber manufactured in this country and one foreign synthetic rubber were included in this study. It was necessary to blend Vistanex Medium with natural rubber, inasmuch as this synthetic rubber cannot be vulcanized.

REPORT DOCUMLN I iA I n PAGE Appro701 SOMLB No 0704 0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions. searching exishng dala sources , gathering ar•i maintaining tie data needed, and completing and reviewing the collection of information Send comments regarding this burden estimate or any other aspect of thiS collection of informathon incluC,ng suggestios for reducing this burden, to Washington Headquarlers Services. The effectiveness of applying incoherent change detection to multipass synthetic aperture radar (SAR) images and targets in foliage is affected by the operating radar frequency band. Incoherent change detection is achieved by taking the weighted difference of the magnitude of two well registered passes of SAR imagery. Items which change between two passes, such as a target present in the first pass and not present in the second pass, will appear in the weighted difference image. With well registered wideband SAR imagery, imagec can be divided into frequency bands and evaluated using incoherent change detection. An Environmental Research Institute of Michigan (ERIM) Rail SAR experiment provides such a data collection. The Rail SAR is characterized by polarimetric, wideband (400 MHz -1.3 GHz), multipass (with and without targets), well registered SAR images. The ERIM Rail SAR data is divided into a number of frequency bands which simulate the high-band Stanford Research Institute, International (SRI) Ultra-WideBand Radar (UWBR) (350-550 MHz), the Loral miniature SAR (MSAR) (500-800 MHz), and the Naval Air Warfare Center (NAWC) P-3 upgraded UWBR (200-900 MHz) sensor. This paper shows how these sensors work on targets in foliage using incoherent change detection and provides an experimental measurement of upper-bound performance. ABSTRACTThe effectiveness of applying incoherent change detection to multipass synthetic aperture radar (SAR) images and targets in foliage is affected by the operating radar frequency band. Incoherent change detection is achieved by taking the weighted difference of the magnitude of two well registeree "',ses of SAR imagery. Items which change between two passes, such as a target present in the first pass and not present in the second pass, will appear in the weighted difference image. With well registered wideband SAR imagery, images can be divided into frequency bands and evaluated using incoherent change detection. An Environmental Research Institute of Michigan (ERIM) Rail SAR experiment provides such a data collection. The Rail SAR is characterized by polarimetric, wideband (400 MHz -1.3 GHz), multipass (with and without targets), well registered SAR images. The ERIM Rail SAR data is divided into a number of frequency bands which simulate the high-band Stanford Research Institute, International (SRI) Ultra-WideBand Radar (UWBR) (350-550 MHz), the Loral miniature SAR (MSAR) (500-800 MHz), and the Naval Air Wartare Center (NAWC) P-3 upgraded UWBR (200-900 MHz) sensor. ...