Development of autoclavable addition type polyimides

Two highly promising approaches to yield autoclavable addition-type polyimides were identified and evaluated in the program. Conditions were established for autoclave preparation of Hercules HMS graphite fiber reinforced composites in the temperature range of 473 K to 505 K under an applied pressure of 0.7 MN/m2 (100 psi) for time durations up to four hours. Upon oven postcure in air at 589 K, composite samples demonstrated high mechanical property retention at 561 K after isothermal aging in air for 1000 hours. Promise was shown for shorter term mechanical property retention at 589 K upon exposure in air at this temperature

Development of autoclavable polyimides

A poly(Diels-Alder) (PDA) resin approach was investigated as a means to achieve autoclavability of high temperature resistant resin/fiber composites under mild fabrication procedures. Low void content Type A-S graphite reinforced composites were autoclave fabricated from a PDA resin/fiber prepared from an acetone:methanol:dioxane varnish. Autoclave conditions were 477K (400F) and 0.7 MN/sq m (100 psi) for up to two hours duration. After postcure at temperatures up to 589K (600F), the composites demonstrated high initial mechanical properties at temperatures up to 561K (550F). The results from isothermal aging studies in air for 1000 hours indicated potential for long-term ( 1000 hours) use at 533K (500F) and shorter-term (up to 1000 hours) at 561K (550F)

Information Efficiency of Binary Communication Systems (Final Report v.I)

Most of the work which has been done with binary communication systems up until now has assumed operation in a symmetric mode. This work is concerned with the problem of evaluating various combinations of modulation and detection in both symmetric and non-symmetric modes of operation. The most frequently used criterion for describing performance in a binary system is total probability of error, A discussion of this and other criteria such as realizable rate and minimum energy per bit factors is given. A new criterion called information efficiency is defined which is based on realizable information rate on a per symbol basis. The primary advantage of this criterion is that it gives a truer indication of performance than probability of error in the case of unsymmetric operation. Several types of conventional binary systems are analyzed and compared under the conditions that additive gaussian white noise is the only perturbing influence. Systems considered include amplitude shift keying or a carrier on-off type of modulation with linear envelope detection and with synchronous detection, phase shift keying of a phase reversal type of modulation with both synchronous and phase comparison detection schemes, Performance curves showing information efficiency and probability of error as functions of signal-to-noise ratio are given. A similar type of analysis is given for a group of matched filter systems which includes both coherent and non-coherent matched filter detection of amplitude and frequency shift keyed signals in the face of gaussiam white noise and the coherent matched filter detection of phase shift keyed signals,, Also included are some results concerning the use of differentially coherent detection of phase shift keyed signals. The response of various systems to variations in decision thresholds is examined and it is shown that phase shift keyed systems are superior in this respect. The optimum detection of amplitude shift keyed signals requires a variable threshold level for different conditions at the detector input, fee case of fixed threshold systems is examined and it is shown that a fixed threshold limits the maximum attainable performance of the system and that there is a distinct trade-off between this maximum possible performance at high signal-to-noise ratios, and good performance (i.e., near optimum) at low signal-to-noise ratios. The problem of Rayleigh fading is discussed and indications of fading on the performance of the various systems is given. Finally, all of the systems discussed are compared on the same basis by using a time bandwidth product which allows the signal-to-noise ratios bn which the conventional system analysis is based to be converted to an energy per symbol to noise spectral density ratio, which is the basis for matched filter analysis

Positioning Airbnb and Fairbnb in the sharing-exchange continuum

Many organizations are positioning themselves as part of the sharing economy due to positive connotations associated with the sharing concept. Recognizing that many of these organizations represent the sharing economy to varying degrees, this study selected two organizations – Airbnb and Fairbnb, to analyze the extent to which they serve as examples of the sharing economy. A content analysis was undertaken to identify the position of each organization on a continuum, ranging from pure sharing to pure exchange characteristics. The analysis reveals that overall Fairbnb may be a stronger example of the sharing economy than Airbnb.info:eu-repo/semantics/acceptedVersio

Variation of turbulent burning rate of methane, methanol, and iso-octane air mixtures with equivalence ratio at elevated pressure

Turbulent burning velocities for premixed methane, methanol, and iso-octane/air mixtures have been experimentally determined for an rms turbulent velocity of 2 m/s and pressure of 0.5 MPa for a wide range of equivalence ratios. Turbulent burning velocity data were derived using high-speed schlieren photography and transient pressure recording; measurements were processed to yield a turbulent mass rate burning velocity, utr. The consistency between the values derived using the two techniques, for all fuels for both fuel-lean and fuel-rich mixtures, was good. Laminar burning measurements were made at the same pressure, temperature, and equivalence ratios as the turbulent cases and laminar burning velocities and Markstein numbers were determined. The equivalence ratio (φ) for peak turbulent burning velocity proved not always coincident with that for laminar burning velocity for the same fuel; for isooctane, the turbulent burning velocity unexpectedly remained high over the range φ = 1 to 2. The ratio of turbulent to laminar burning velocity proved remarkably high for very rich iso-octane/air and lean methane/air mixtures

The development of low temperature curing adhesives

An approach for the development of a practical low temperature (293 K-311 K/68 F-100 F) curing adhesive system based on a family of amide/ester resins was studied and demonstrated. The work was conducted on resin optimization and adhesive compounding studies. An improved preparative method was demonstrated which involved the reaction of an amine-alcohol precursor, in a DMF solution with acid chloride. Experimental studies indicated that an adhesive formulation containing aluminum powder provided the best performance when used in conjunction with a commercial primer

Perfect Reflection of Light by an Oscillating Dipole

We show theoretically that a directional dipole wave can be perfectly reflected by a single point-like oscillating dipole. Furthermore, we find that in the case of a strongly focused plane wave up to 85 % of the incident light can be reflected by the dipole. Our results hold for the full spectrum of the electromagnetic interactions and have immediate implications for achieving strong coupling between a single propagating photon and a single quantum emitter.Comment: 3 figure

Are infestations of Cymomelanodactylus killing Acropora cytherea in the Chagos archipelago?

Associations between branching corals and infaunal crabs are well known, mostly due to the beneficial effects of Trapezia and Tetralia crabs in protecting host corals from crown-of-thorns starfish (e.g., Pratchett et al. 2000) and/or sedimentation (Stewart et al. 2006). These crabs are obligate associates of live corals and highly prevalent across suitable coral hosts, with 1–2 individuals per colony (Patton 1994). Cymo melanodactylus (Fig. 1) are also prevalent in branching corals, mostly Acropora, and are known to feed on live coral tissue, but are generally found in low abundance (<3 per colony) and do not significantly affect their host corals (e.g., Patton 1994). In the Chagos archipelago, however, infestations of Cymo melanodactylus were found on recently dead and dying colonies of Acropora cytherea