Investigation of thermal decomposition of polymer nanocomposites with different char residues

The pyrolysis process of polypropylene (PP), PP‐based nanoclay composites, acrylonitrile‐butadiene‐styrene (ABS), and ABS/metal hydroxide nanorods (MHR)/grapheme nanosheets (GNS) composites in a cone calorimeter test was simulated with a recently developed numerical codes, the Federal Aviation Administration ThermaKin. First, the heat release rate (HRR) and the surface temperature as a function of time were compared with experiment data. With reasonable input parameters, the pyrolysis behaviors were predicted reasonably. Subsequently, the influence of the properties of char residue on the HRR was discussed. The char residue of PP/nanoclay acted as a heat transfer barrier, while the char layer of ABS/MHR/GNS acted as a mass transfer barrier. Finally, the sensitivity of the residue characteristic parameters to the model output was discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal Guidance for Quasi-planar Lunar Ascent

The minimum-time controls (thrust pitch angle and thrust yaw angle) for the three-dimensional transfer of a constant-thrust rocket from one state to another over a flat moon are used to develop guidance laws for operation over a spherical moon. The objective is to evaluate the effect of making approximations on the size of the thrust pitch angle on the suitability of the resulting control law as a guidance law. After assuming small out-of-plane motion (small yaw angle), three pitch angle control laws (exact, first-order, and zeroth-order) are developed. The three laws are employed in the sample and hold guidance of a lunar ascent vehicle. All three laws satisfy the final conditions and give essentially the same pitch and yaw control histories. Since the zeroth-order law can be obtained completely analytically (no iteration processes), it merits consideration for ascent guidance.     

High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2

The structural properties of the binary alkaline-earth halides SrCl₂, SrBr₂, BaCl₂ and BaBr₂ have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl₂ undergoes a gradual transition to a superionic phase at 900–1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr₂ undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl₂. BaCl₂ and BaBr₂ both adopt the cotunnite crystal structure under ambient conditions. BaCl₂ undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored.     

Investigation of the thermal decomposition and flammability of PEEK and its carbon and glass-fibre composites

Conventional thermally durable materials such as metals are being replaced with heat resistant engineering polymers and their composites in applications where burn-through resistance and structural integrity after exposure to fire are required. Poly aryl ether ether ketone (PEEK) is one such engineering polymer. Little work has been published with regards to the flammability of PEEK and its filled composites. The current study aims to assess the flammability and fire behaviour of PEEK and its composites using thermogravimetric analysis, pyrolysis combustion flow calorimetry, limiting oxygen index, a vertical flame resistance test, and fire (cone) calorimetry.     

Highly efficient D2 generation by dehydrogenation of formic acid in D2O through H+/D+ exchange on an iridium catalyst: application to the synthesis of deuterated compounds by transfer deuterogenation

Deuterated compounds have received increasing attention in both academia and industrial fields. However, preparations of these compounds are limited for both economic and practical reasons. Herein, convenient generation of deuterium gas (D(2)) and the preparation of deuterated compounds on a laboratory scale are demonstrated by using a half-sandwich iridium complex with 4,4'-dihydroxy-2,2'-bipyridine. The "umpolung" (i.e., reversal of polarity) of a hydrogen atom of water was achieved in consecutive reactions, that is, a cationic H(+)/D(+) exchange reaction and anionic hydride or deuteride transfer, under mild conditions. Selective D(2) evolution (purity up to 89?%) was achieved by using HCO(2)H as an electron source and D(2)O as a deuterium source; a rhodium analogue provided HD gas (98?%) under similar conditions. Furthermore, pressurized D(2) (98?%) without CO gas was generated by using DCO(2)D in D(2)O in a glass autoclave. Transfer deuterogenation of ketones gave α-deuterated alcohols with almost quantitative yields and high deuterium content by using HCO(2)H in D(2)O. Mechanistic studies show that the H(+)/D(+) exchange reaction in the iridium hydride complex was much faster than β-elimination and hydride (deuteride) transfer.     

Development of proposed federal standard 1070: 62.5/125-μm graded-index,multimode optical fiber waveguides for on-premises applications

This paper describes a process that has been successful in generating a specification to guide the user community in the procurement of single-size, multimode optical fiber for on-premises applications. This process began with an attempt to adopt an industry standard as a federal standard that would eliminate a multiplicity of choices available from the marketplace. The initial EIA-458-A Standard contained four “preferred” sizes. Discussions both in a government standards committee and in an applications-oriented industry (EIA) working group indicated the desirability of recommending a single fiber size. The process by which the industry committee selected the 62.5-μm core diameter/125-μm cladding diameter multimode fiber is presented.

The next element of the process was that of selecting the appropriate standard performance measures and attributes that would assure minimum performance of graded parameters such as attenuation and bandwidth, as well as a uniform specification of the product. The vehicle selected for this specification was the EIA 492-Series Generic, Sectional, and Blank Detail Specifications. Inputs were solicited from all of the identified U.S. manufacturers of this fiber size. Those inputs were coordinated and integrated into a detail specification, which is now being circulated by the EIA on a standards proposal ballot. After ballot approval, it will be published as an ANSIIEIA standard specification. Similar work has been initiated to develop a detail specification for fiber optic cables based on a related set (472-Series) of EIA specifications.

The process of developing a detail specification that assures conformance of the product to dimensional and strength tolerances as well as performance measures requires considerable coordination and iteration. No proprietary information or processes are contained in the specification so that the industry participants are free to compete on price and performance as long as compliance with the specification can be demonstrated.     

Characterization techniques for a MEMS electric-field sensor in vacuum

An accurate calibration of an electric-field sensor is difficult to carry out due to challenges involved in generating a uniform electric field over the sensor volume. Additionally, capacitive coupling between the field source and the sensors and related instrumentation tends to distort the measured field further. Sensor characterization includes not only calibration, but also determination of the frequency response (both magnitude and phase), noise power spectral density, dynamic range, and linearity. In this paper, we discuss characterization techniques for an unpackaged microelectromechanical systems (MEMS) electric field sensor in a vacuum chamber. The use of oppositely charged square plates at a spacing of half the plate width is advised by the IEEE 1308-1994 standard for generation of a uniform electric field. Previously, the U.S. Army Research Laboratory (ARL) has shown that by employing guard tubes in the construction of an electric field generating chamber, the fringing fields can be controlled, and the spacing between the endplates can be increased while maintaining a uniform field. A similar, smaller apparatus for generating a uniform axial electric field was constructed to fit into a vacuum bell jar. The considerations and techniques for minimizing error due to fringing and distortion from metal conductors will be presented, along with the techniques and laboratory equipment used for characterizing the sensor.     

Equation of state of 7LiD up to 6 GPa from neutron powder diffraction experiments

Abstract

The equation of state of ⁷LiD has been measured at 300 K up to 6GPa by 90° time-of-flight neutron scattering methods, in a novel cell with toroidal anvils. The increased precision over previous data allows to check theoretical calculations on lithium hydrides.

L'équation d'état de ⁷LiD a été établie à 300 K jusqu'à 6 GPa par des mesures de durée de vol de neutrons diffractés à 90°, dans une cellule à enclumes toroidales de conception originale. La prkision de ces mesures permet un test significatif des calculs théoriques sur les hydrures de lithium.     

Light induced fading in the OSL response of Al2O3:C

We are reporting the results of an investigation designed to determine the magnitude of the light induced fading associated with the OSL response of Al₂O₃:C. Unlike previous studies where bare, radiation sensitive OSL elements were exposed directly to light, most of the experiments described here were conducted using sealed commercially available OSL dosimeters. During light exposure the OSL sensitive elements were kept inside a standard commercially available plastic badge. A commercial OSL system was used for these experiments in an attempt to simulate typical field use conditions. Both light induced signal and light induced fading were considered, however no measurable light induced signal could be identified. Light induced fading effects, however, were significant, up to 55% loss of OSL signal following daylight exposure of 45 days. The possibility that dose information may be easily erased, intentionally or accidentally, could impose significant restrictions on the ability of the US Navy to defend, if needed, the reported personnel dose levels.     

Einstein Supergravity and New Twistor String Theories

A family of new twistor string theories is constructed and shown to be free from world-sheet anomalies. The spectra in space-time are calculated and shown to give Einstein supergravities with second order field equations instead of the higher derivative conformal supergravities that arose from earlier twistor strings. The theories include one with the spectrum of N = 8 supergravity, another with the spectrum of N = 4 supergravity coupled to N = 4 super-Yang-Mills, and a family with N ≥ 0 supersymmetries with the spectra of self-dual supergravity coupled to self-dual super-Yang-Mills. The non-supersymmetric string with N = 0 gives self-dual gravity coupled to self-dual Yang-Mills and a scalar. A three-graviton amplitude is calculated for the N = 8 and N = 4 theories and shown to give a result consistent with the cubic interaction of Einstein supergravity.